Henrys Fork Island Park Caldera Reach Evaluation: Hydrology, Geomorphology, and Sediment Transport

Transcription

1 Henrys Fork Island Park Caldera Reach Evaluation: Hydrology, Geomorphology, and Sediment Transport With Specific Recommendations for a Peak Flow Release to Improve Aquatic Habitat Prepared For: Prepared by: July, 2012

2 ACKNOWLEDGEMENTS This report is the result of the coordinated efforts of a large team committed to preserving, protecting, and restoring the Henrys Fork and would not have been possible without the valuable contributions of Jim DeRito, Steve Trafton, Trevor Perkes, and Anne Marie Emery Miller of the Henrys Fork Foundation and Adonia Henry. I

3 TABLE OF CONTENTS Executive Summary... i Problem Statement... i Data Collection and Analysis... i Results... i Implications for Future Management and Additional Studies... iii 1 Introduction and Purpose Project Setting Geology Hydrology Geomorphology, Sediment Transport, and Channel Morphology Hydrogeomorphic Evaluation Hydrology... 7 Flood Frequency Analysis Flow Duration Analysis Historical Aerial Photography Channel Geometry Channel Bed Sediments Facies Mapping Pebble Counts Bulk Samples Channel Bed Sediment Trends and Distribution Hydraulic and Sediment Transport Modeling Approach Models Model Construction and Set up Model results Peak Flow Release Recommendations Peak Flow Release Hydrograph Flushing Flow Sediment Transport Monitoring Plan I

4 Suspended Sediment Sampling Bedload Sediment Sampling Tracers Particles Scour Chains (Optional) Proposed High Peak Flow Monitoring Data Post-Processing Conclusion and Next Steps References Appendix A Pebble Count Data II

5 EXECUTIVE SUMMARY PROBLEM STATEMENT During an emergency drawdown of the Island Park Reservoir in September of 1992, between 50,000 and 100,000 tons of fine sediment was deposited in the Caldera Reach of the Henrys Fork of the Snake River (HabiTech 1994). After the accidental release, significant deposits of fine sediment were observed in the channel and rainbow trout abundance appeared to decrease. The purpose of this report is to improve the understanding of the geomorphic processes of the Caldera Reach and to propose measures to improve habitat within the Caldera Reach where it is still impacted by the 1992 accidental fine sediment release. DATA COLLECTION AND ANALYSIS To improve the understanding of geomorphic processes and identify measures to improve habitat, we evaluated hydrology, geomorphology, and sediment transport in the Caldera Reach of the Henrys Fork. We reviewed existing reports and studies to provide context for the geologic, hydrologic, geomorphic, sediment transport, and channel morphology setting. Based on our review of existing data sources we identified and completed the following study tasks: - Developed a synthetic hydrograph for the Henrys Fork in the Caldera Reach (including Buffalo River inflows) and conducted flood frequency analysis and flow duration analysis; - Collected and rectified historical aerial photographs of the Caldera Reach, incorporated them into a project Geographic Information System (GIS), and performed historical aerial photography analysis of channel change; - Surveyed cross sections to adequately capture the channel geometry for use in hydraulic and sediment transport modeling and surveyed a continuous water surface profile along the study reach for hydraulic model calibration; - Characterized the channel bed composition by conducting facies mapping, pebble counts, and bulk samples - Performed hydraulic and sediment transport modeling to determine bed mobilization at different flows; - Recommended a peak flow hydrograph to flush fine sediment from the channel bed and developed a flushing flow sediment transport monitoring plan. RESULTS The results of our data collection and analysis provide a comprehensive understanding of geomorphic conditions in the study reach, provide a baseline for a flushing flow release, and identify additional studies and implications for future management. The results from our analysis are summarized below. I

6 Analysis of background information for the study reach is provided in Section 2, Project Setting. Our review of existing data identified that the channel meanders through alluvium, tholeiite, and thyolite geologic units (Newhall and Dzurisin 1998). The well drained volcanic geology in the watershed results in a strong connection between surface water and groundwater. Groundwater springs provide consistent discharge to the channel through the late summer, fall, and winter. The Buffalo River is the only major tributary in the study reach, and hydrogeology is strongly influenced by snowmelt in the spring months. Island Park Dam was constructed in 1939 and operations lower winter discharge and increase late summer discharge (Van Kirk and Burnett 2004; Gregory 2008). Island Park Dam impacts sediment transport by trapping coarse sediment upstream of the Caldera Reach, and dam operations allow peak flows from spring and summer snowmelt to pass through the reservoir with similar magnitude and timing as the pre-dam condition. Channel geometry is shallow and wide and stable over time, largely due to access to a wide floodplain. Previous studies (HabiTech 1994; 1998; Minshall et al. 1993; Van Kirk and Griffin 1997) show that sediment is transported at flows greater than 2,000 cfs, and that large inputs of fine sediment from Island Park Reservoir occurred in 1966, 1979, and Lastly, the life cycle of macrophytes (rooted aquatic plants) influence the channel morphology and have a large impact on the physical and ecological conditions that sustain the wild trout fishery on the Henrys Fork (Henry 2010; Shea et al. 1996). Our hydrogeomorphic evaluation of the study reach addressed hydrology, historical aerial photography, channel geometry, channel bed sediment composition, and hydraulic and sediment transport modeling. The methods and results for each analysis are presented in Section 3, Hydrogeomorphic Evaluation. First, we investigated hydrology and constructed a synthetic hydrograph for the Henrys Fork to incorporate inflows from the Buffalo River, a major tributary to the Henrys Fork located downstream of the long-term USGS gage on the Henrys Fork. To incorporate discharge from the Buffalo River we followed the method outlined in Van Kirk and Burnet (2004) and used the short-term USGS gage data on the Buffalo River and recent individual discharge measurements from the Buffalo River. The synthetic mean daily hydrograph for the Henrys Fork shows flows that range from 300 3,250 cfs. We conducted a flood frequency analysis for the Island Park Gage from 1933 to 2010 and determined that the Q 2, Q 50, and Q 100 were 1,863, 2,908, and 3,102 respectively. We conducted a flow duration analysis and found that 95% of the days in the period of record had a flow less than or equal to 1,500 cfs. Our hydrology analysis showed that the Henrys Fork has a relatively consistent annual hydrograph. Our analysis of the channel using historical aerial photographs (Section 3.2 of this report) showed that the study reach has experienced very little change from 1953 to 2009 in channel planform and alignment. Based on our the channel geometry and profile data we collected, we characterized the channel geometry into four different types: 1) plain bed, 2) bend, 3) constricted chute, and 4) island. We characterized the channel as wide and shallow with access to a broad floodplain, except for the narrow chute and island side channels. In Section 3.4 we report the results of our channel bed sediment analysis from facies mapping, pebble counts, and bulk samples. Our facies map shows that the channel bed area in the study reach is composed of 61% gravel, 28% sand, 7% bedrock, and 4% silt. We conducted 18 pebble counts and 8 bulk samples that show gradual fining of bed materials in the downstream direction, lateral variation in bed sediments, isolated patches of fine sediments between Big Bend, II

7 the confluence of Fish Creek, and the tail end of Millionaire s Pool. We conducted hydraulic and sediment transport modeling, which we describe in Section 3.5. We calibrated the model using the longitudinal water surface elevation profile from our data collection effort and conducted bed mobility modeling at flows ranging from 350 cfs to 3,500 cfs. At 350 cfs we found little to no predicted channel bed mobilization, while at 3,500 cfs significant channel bed mobilization. Additionally, we modeled bed sediment mobility at Big Bend and Millionaire s Pool for a scenario with a constructed island in the channel to concentrate flow and increase mobility. We found that construction of islands can increase mobility downstream of Millionaire s Pool, but initial runs with constructed islands at Big Bend don t appear to significantly increase mobility. Additional model iterations would be required to improve the size and placement of a constructed island at Big Bend to optimize bed mobility. IMPLICATIONS FOR FUTURE MANAGEMENT AND ADDITIONAL STUDIES Based on our review of existing studies and reports on the Henrys Fork (Section 2) and the results of the hydrogeomorphic evaluation (Section 3) we developed a peak flow release hydrograph to mobilize the bed sediments in the study reach and a flushing flow sediment transport monitoring plan. Both the peak flow hydrograph and sediment transport monitoring plan are described in greater detail in Section 4. Lastly, we summarized the conclusion of this report and recommend next steps in Section 5. The purpose of a peak flow hydrograph is to mobilize accumulated fine sediments in the channel, with the ultimate goal of improving habitat conditions that were impacted by the large release of fine sediment from Island Park Reservoir in In addition, the peak flow hydrograph and sediment transport monitoring plan could also be used to improve management approaches for future fine sediment releases from Island Park Reservoir. The peak flow hydrograph combines releases from Island Park Reservoir and the discharge from Buffalo River. Our peak flow hydrograph (Section 4.1) ramps up from the base flow to plateaus of 1,000, 2,000, and 2,500 cfs where flows are held constant to conduct sediment transport monitoring. Our proposed peak flow of 3,000 cfs shold be maintained for one day to allow for sediment transport monitoring and the flow will be held constant at 2,750 and 2,500 cfs for monitoring while ramping back down to the base flow. Our proposed peak flow hydrograph requires 5 days and was planned for mid-april 2011 to take advantage of spring runoff. To evaluate the peak flow release and to refine our understanding of the hydraulics, sediment transport dynamics, and relationships between sediment, macrophyte communities, and channel morphology we developed a sediment transport monitoring plan in Section 4.2. The sediment transport monitoring plan specifies monitoring locations, suspended sediment and bedload sampling methods, and flow velocity and discharge sampling methods. We propose monitoring before, during, and after the peak flow release. We recommend sediment transport monitoring include suspended and bedload sediment sampling, tracer gravel placements, and optionally, scour chain installations. In addition, we recommend aquatic vegetation monitoring be conducted before III

8 and after the peak flow release at previously monitored transects that coincide with the sediment transport sampling transects. In Section 5, we recommend additional studies and analyses including comparisons between cross sections surveyed for this report and cross sections presented in Henry (2010), and development of a history of macrophyte abundance from 1988 to 2011 using data collected by Jeff Snyder and Henry (2010). These analyses would help further the understanding of the impacts of both accidental fine sediment releases and ice flow events on macrophyte abundance. IV

9 1 INTRODUCTION AND PURPOSE The Henrys Fork of the Snake River in eastern Idaho is one of the most important and well-known recreational fisheries in the United States. The Henrys Fork Foundation, a non-profit organization dedicated to preserving, protecting, and restoring the watershed, has catalyzed a variety of fisheries habitat research and restoration work in the watershed since the early 1980 s. Much of this research and restoration has focused on the Island Park Caldera Reach of the Henrys Fork. This reach extends approximately 16 miles from Island Park Dam south to the Riverside Campground (Figure 1) and includes Harriman State Park with its world renowned rainbow trout angling spots Millionaire s Pool and Big Bend. The overarching goal of the research and restoration efforts in the Caldera Reach has been to understand, and ultimately improve, aquatic habitat, specifically summer adult rainbow trout habitat, macroinvertebrate habitat, and conditions that improve persistence of macrophytes through the winter to enhance young-of-the-year rainbow trout survival. Channel bed sediment composition and transport in the Caldera Reach is one of the most important influences on rainbow trout habitat. A major accidental release of water from Island Park Reservoir in September of 1992 deposited between 50,000 and 100,000 tons of fine sediment in the Caldera Reach (HabiTech 1994). While detailed quantification and mapping of the deposited fine sediment was not completed, anecdotal reports from researchers and anglers on the Henrys Fork noted significant deposits of fine sediment and reduced populations of rainbow trout. Working in close collaboration with the Henrys Fork Foundation, NewFields initiated hydrologic, hydraulic, geomorphic, and sediment transport investigations and analyses in April 2010 to improve the understanding of natural geomorphic processes in the Caldera reach and identify measures with the greatest potential to improve habitat in areas still impacted by the 1992 fine sediment deposition. More specifically, we completed the following study tasks: Historical analysis of Henrys Fork and Buffalo River hydrology; Channel morphology and bed sediment characterization in the Caldera Reach; Two dimensional hydraulic and sediment transport model development and analysis of the Caldera Reach; Peak flow release and monitoring program design for the Caldera Reach; Channel form manipulation analysis to quantify the potential influence of instream structures on sediment transport dynamics; Refinement of the existing conceptual model of sediment / macrophyte interaction. This report is intended to serve as both a repository for the methods and results of the tasks described above, and as a reference to guide an eventual peak flow release to mobilize bed sediment and enhance rainbow trout habitat. A peak flow release was planned for Spring 2011 but was cancelled just prior to implementation due to concerns raised by PacifiCorp regarding dam 1

10 maintenance work in progress downstream. We recommend that this report be updated once the peak flow release and related monitoring has been completed. 1 PROJECT SETTING The Henrys Fork is a major tributary to the Snake River. Its watershed is located in southeastern Idaho, with the headwaters draining the Continental Divide along the Idaho-Montana border, and a small portion of the watershed in Wyoming draining Yellowstone National Park adjacent to the Teton Mountain Range. The total watershed area is approximately 3,212 square miles. This study focuses on the Caldera Reach of the river, which begins at the outlet of Island Park Dam and flows generally south through a broad, flat meadow in the Island Park Caldera (a volcanic crater) in central Fremont County. This stretch of river includes the Box Canyon, Last Chance, Railroad Ranch, Harriman State Park, and Pinehaven reaches, and ends at the Riverside Campground above Mesa Falls. The Buffalo River, a major tributary, joins the Henrys Fork immediately downstream of Island Park Dam. Other tributaries along this section include Blue Springs Creek, Antelope Park Creek, Big Bend Creek, Thurmon Creek, and Fish Creek (Figure 1). 2

11 FIGURE 1. HENRYS FORK CALDERA REACH REGIONAL MAP AND STUDY AREA. 2.1 GEOLOGY The geology of the area is defined by the Henrys Fork Caldera, which sits inside the Island Park Caldera. Both calderas are influenced by the Yellowstone Hotspot and were formed by the eruption of a supervolcano approximately 1.3 million years before present (Newhall and Dzurisin 1988). The Henrys Fork Caldera is approximately 18 miles long and 23 miles wide, and its curved rim 3

12 is visible from most locations inside the caldera. Figure 2 shows the primary geologic units in the Henrys Fork Caldera and vicinity, with the Caldera Reach meandering through alluvium, tholeiite, and rhyolite. FIGURE 2. HENRYS FORK CALDERA REACH REGIONAL GEOLOGY MAP. 4

13 1P P as P of 2.2 HYDROLOGY The hydrology of the Caldera Reach is strongly influenced by snowmelt-driven runoff processes in the spring months, with peak flows typically occurring between April and July. The volcanic geology of the region results in highly connected groundwater and surface water, and inflows from groundwater-fed springs provide a relatively constant discharge through the late summer, fall, and winter seasons. Current hydrology is influenced by operations at Island Park Dam (constructed in 1939), which stores and releases water primarily to satisfy irrigation demands. Historically, the dam has had a variety of impacts on streamflows in the Caldera reach, most significantly lowering winter discharge, increasing late summer discharge, lowering annual peak discharge, and shifting peak discharge to slightly later in the year (Van Kirk and Burnett 2004). Prior to 1972, winter operations frequently cut off flows into the Caldera Reach for 30 to over 90 days at a time, resulting in major impacts on rainbow trout habitat and other flow-dependent elements of the Henrys Fork ecosystem. Starting in 1972, the winter storage season was lengthened, increasing the operational flexibility of Island Park Dam and maintaining some outflow during the winter months, although often at very low levels, especially during years of drought. In 2003, the Fremont-Madison Conveyance Act mandated drought management planning for the Caldera reach of the Henrys Fork. This enabled entities with an interest in fisheries management (including the Henrys Fork Foundation, Trout Unlimited, The Nature Conservancy, and the Idaho Department of Fish and Game) to assist in the management of Island Park Dam for the benefit of the downstream wild trout fishery. Since 2003, early winter flow releases have been curtailed in the winter storage season (November 1 to April 1) to achieve higher late winter flows (Gregory 2008). 2.3 GEOMORPHOLOGY, SEDIMENT TRANSPORT, AND CHANNEL MORPHOLOGY The existing channel morphology in the Caldera Reach appears mostly natural but has been impacted by alterations to the river and its watershed. First, and perhaps most importantly, Island Park Dam traps coarse sediment generated in the watershed and prevents it from being transported into the Caldera Reach. In addition, Island Park Dam operations maximize water storage with the st objective of filling the reservoir by April 1P each year. Therefore, peak flows that occur after April st a result of spring and summer snowmelt tend to pass through the reservoir with similar magnitude and timing as would occur naturally. This means that the current frequency of high peak flows capable of mobilizing channel bed sediment is only slightly altered by the dam and reservoir (Van Kirk and Burnett 2004). However, because watershed hydrology is largely controlled by springfed inflows, flows capable of mobilizing and substantially redistributing channel bed sediments tend to be extremely rare under both pre-dam and post-dam hydrology (Gregory 2008). Because Island Park dam predates all but the earliest aerial photography, we have only a limited understanding of the channel morphology in the Caldera Reach prior to the influence of the dam. Presently, the general character of the Henrys Fork channel through the Caldera Reach is controlled 5

14 by local topography, which consists of a low gradient, flat, and wide valley bottom. As the Henrys Fork meanders through this valley bottom, the channel is almost uniformly shallow and wide. The lack of confining topography, spring-fed hydrology, and access to a wide floodplain area all contribute to the Caldera Reach having relatively low hydraulic energy and remaining quite stable over long periods of time. This also contributes to the tendency for the Caldera Reach to store fine sediments (especially along channel margins and in the interstices between gravel and cobble bed materials) for relatively long periods. Sediment transport investigations in the 1990s determined that the Caldera Reach transports significant volumes of fine sediment during high flow conditions (i.e. greater than approximately 2,000 cfs), but almost no bedload at flows less than 3,000 cfs (HabiTech 1994; 1998). These previous studies occurred before and after a flushing flow of ~2,600 cfs was released from Island Park Dam for four days starting on May 17, While these studies didn t directly quantify the effect that the flushing flow had on channel bed sediments and channel morphology, they did determine that fine gravels (suitable for rainbow trout spawning) were at least partially mobilized at 2,600 cfs, but no cobbles at the margin of the channel were likely to be mobilized at flows less than 3,000 cfs. In addition, these studies posited that the effectiveness of the flushing flow to mobilize bed sediments may have been limited by the increased macrophyte growth that occurs in late spring, and that a peak flow earlier in the year may have been more effective in mobilizing bed sediments (Gregory 2008). Bed sediment mobilization is very important when considered in the context of the history of accidental inputs of large volumes of fine sediment to the Caldera Reach in the past several decades (1966, 1979, and 1992). The accidental release from Island Park Dam in 1992 transported an estimated 50,000 to 100,000 tons of fine sediment into the Caldera reach (Minshall et al. 1993; Van Kirk and Griffin 1997). Unfortunately, sediment size distributions, areas of deposition, and rates of downstream transport associated with this most recent event were not carefully measured at the time of the sediment release. Anecdotal observations over the last twenty years and more detailed observations and measurements conducted for this study suggest that fine sediments have a long residence time in the Caldera Reach and are an important aspect of the sub-reach scale channel morphology and aquatic habitat. The annual growth and death of macrophytes (rooted aquatic plants) on the channel bed throughout the Caldera Reach also appears to strongly influence sub-reach scale channel morphology and aquatic habitat by interacting with and modifying channel structure and sediment mobility. Macrophytes have a substantial influence on channel roughness, flow velocity distributions, water depth, and sediment deposition and erosion processes. Macrophyte extent and distribution throughout the Caldera reach has varied historically as a result of flow management at Island Park Dam (which influences the effects of icing and scour), waterfowl grazing, and sediment deposition. Macrophytes also have a large influence on the physical and ecological conditions vital to sustain the wild trout fishery in the Henrys Fork (Shea et al. 1996). Recent investigations of 6

15 aquatic macrophytes (Henry 2010) indicate that percent cover by aquatic macrophytes was significantly lower in 2009 than in 1993, 1994, or HYDROGEOMORPHIC EVALUATION This study augments the existing body of research on the Caldera Reach of the Henrys Fork River by adding detail to the hydrologic, hydraulic, geomorphic, and sediment transport processes that influence the river ecosystem and sustainability of the wild trout fishery in the Caldera Reach. The Caldera Reach spans a continuous gradient of geomorphic features that have been created and maintained by the hydrologic, hydraulic, and sediment transport processes active in these reaches of the Henrys Fork. We characterized historical and current geomorphic features and processes in the Caldera Reach to document and understand general geomorphic trajectories and to provide critical information to guide our data collection and hydraulic and sediment transport model development. We used the following methods to characterize existing fluvial geomorphic features and processes: Review and interpretation of existing geomorphic literature on the Caldera reach (described preceding sections) Assessment of historical and modern hydrology Interpretation of historical and recent aerial photography Evaluation of existing conditions hydraulics Characterization of surface and subsurface sediments in the Caldera reach The following sections describe these investigations in more detail. 3.1 HYDROLOGY We developed a synthetic long term hydrologic record for the Henrys Fork downstream of the confluence with the Buffalo River, analyzed flood frequency in the Caldera Reach, and determined flow durations for the period of record. The USGS has maintained a gage downstream of Island Park reservoir from 1933 to present (USGS HENRYS FORK NR ISLAND PARK ID). The Buffalo River is a tributary to the Henrys Fork and the confluence is located downstream of the Island Park gage. The USGS also maintained a gage on the Buffalo River from 10/1/1935 to 1/2/1941 (USGS BUFFALO RIVER AT ISLAND PARK ID; Table 1; Figure 1). More recently, Mr. David Boyter has made daily discharge measurements on the Buffalo River approximately one mile upstream from the confluence with the Henrys Fork and just downstream of the Highway 20 bridge from 1/1/2007 to 12/31/2010. Daily stages were recorded and discharges were obtained from a recently updated USGS rating curve for the Buffalo River. TABLE 1. HENRYS FORK AND BUFFALO RIVER HYDROLOGY DATA. Gage Name USGS ID Period of Record Henrys Fork nr Island Park ID /1/1933 to 12/31/2010 Buffalo River at Island Park ID /1/1935 to 1/2/1941 Buffalo River 1/1/2007 to 12/31/2010 7

16 We adopted the method utilized by Van Kirk and Burnet (2004) to estimate long term hydrology for the Buffalo River, using the assumption that the Buffalo River is a large, unregulated tributary that is fed primarily by groundwater and displays little year-to-year variability in daily flow. Van Kirk and Burnet (2004) estimated discharge in the Henrys Fork downstream of the confluence with the Buffalo River by adding to daily flow measured at the Island Park gage the daily mean flow for water years (plus a few days in water years 1935 and 1941) measured in the Buffalo River near its confluence with the Henrys Fork (Figure 3). We calculated the average daily discharge in the Buffalo River using both the 1935 to 1941 and the 2007 to 2010 streamflow measurements. The calculated daily discharge for the Buffalo River was added to the measured discharge in the Henrys Fork at the Island Park gage to estimate the historical daily average discharge in the Henrys Fork River downstream of the confluence with the Buffalo River (Figure 4). Discharge (cfs) Average Oct 31-Oct30-Nov31-Dec 30-Jan 1-Mar 31-Mar30-Apr31-May30-Jun 31-Jul 30-Aug29-Sep Month and Day FIGURE 3. BUFFALO RIVER MEASURED DAILY DISCHARGE FOR AND

17 3,500 3,000 2,500 Discharge (cfs) 2,000 1,500 1, Jan-33 Jan-37 Jan-41 Jan-45 Jan-49 Jan-53 Jan-57 Jan-61 Jan-65 Jan-69 Date (month-year) FIGURE 4. HISTORICAL MEAN DAILY DISCHARGE FOR THE HENRYS FORK DOWNSTREAM OF THE CONFLUENCE WITH THE BUFFALO RIVER. Figure 5 illustrates features of a typical annual hydrograph for the Henrys Fork downstream of its confluence with the Buffalo River: Jan-73 Jan-77 Jan-81 Jan-85 Jan-89 Jan-93 Jan-97 Jan-01 Jan-05 Jan-09 Annual minimum flow of approximately 400 cfs between early October and late November Stable base flow of approximately 600 cfs from mid-december through mid-april First annual peak flows greater than 1,200 cfs from mid-april to mid-june Second annual peak flow (for irrigation deliveries) from early July through mid August Descending limb of winter / spring hydrograph mid-august to September 9

18 1,600 1,400 1st Annual Peak Flow 2nd Annual Peak Flow 1,200 Discharge (CFS) 1, Annual Minimum Flow 400 Descending Limb Base Flow Oct 31-Oct 30-Nov 31-Dec 30-Jan 2-Mar 1-Apr Date 2-May 1-Jun 2-Jul 1-Aug 1-Sep FIGURE 5.TYPICAL ANNUAL HYDROGRAPH FOR THE HENRYS FORK DOWNSTREAM OF THE CONFLUENCE WITH THE BUFFALO RIVER, BASED ON WATER YEARS 2009 AND Although the initial peak flows that occur between April and June are consistent with natural spring snowmelt runoff processes, the second peak from July to August is a product of operations at Island Park Dam for agricultural deliveries and occurs in the middle of summer when macrophyte growth is most dense. Gregory (2008) speculated that higher water levels (due to the artificial peak discharges between July and August), lower velocities in the center of the channel due to the additional roughness from macrophytes, and reduced bed erosion and scour due to slower velocities and the armoring effect of the vegetation may lead to erosive forces being directed towards the channel margins. FLOOD FREQUENCY ANALYSIS A flood frequency analysis is used to determine the statistical probability that a peak flow of a certain magnitude will occur during a certain period of time on a given river. The primary output from a flood frequency analysis is a set of return periods that represent the expected annual frequency for peak flows of designated magnitudes. We used the standard flood frequency analysis method documented in Bulletin 17B (US Geological Survey 1982) to conduct flood frequency analyses for the USGS Henrys Fork near Island Park, ID gage (upstream of the Buffalo River) using the Hydrologic Engineering Center Statistical Software Package (HEC-SSP; United States Army Corps of Engineers 2010). No peak discharge records exist for the Buffalo River and the 10

19 resulting flood frequency analysis will slightly under predict the peak discharge for the Henrys Fork downstream of the confluence with the Buffalo River. Figure 6 shows annual peak flows for the period of record and Table 2 summarizes the results of the flood frequency analysis. 3,000 2,500 F lo w (cfs) 2,000 1,500 1, ISLAND PARK ID USGS FLOW-ANNUAL PEAK FIGURE 6. ANNUAL PEAK FLOWS FOR USGS HENRYS FORK NR ISLAND PARK ID. 11

20 TABLE 2. BULLETIN 17B FLOOD FREQUENCY ANALYSIS RESULTS FOR USGS HENRYS FORK NR ISLAND PARK ID. Recurrence Interval (years) Computed Flow (cfs) Expected Flow (cfs) 5% Confidence Limit 95% Confidence Limit Note that the expected flows reported in Table 2 correct for estimated bias in the frequency curve computation associated with the duration of the analyzed period of record (shorter periods of record have greater expected probability flow adjustments). The expected probability curve is a statistical adjustment that is most often used to establish design flood criteria (USGS 1982).The flood frequency analysis results reinforce our understanding of the Henrys Fork as a relatively low energy river system. Annual peak discharge for the 100-year peak is less than three times greater than for the 1-year peak. In addition, Figure 6 illustrates how the completion of Island Park Dam in 1939 did not significantly alter the magnitude or variability of annual flood peaks. FLOW DURATION ANALYSIS Flow duration analysis determines the percentage of time that a given flow has occurred in a river at a given site. We computed flow durations for the Caldera Reach using HEC-SSP and daily flow data input from the USGS Henrys Fork near Island Park, ID gage (Figure 7) for the complete period of record (3/1/1933 to 12/31/2010). 12

21 3,500 3,000 2,500 F LO W in CF S 2,000 1,500 1, Percent of Time Exceeded Interpolated Curve Computed Curve FIGURE 7. FLOW DURATION CURVE FOR USGS HENRYS FORK NR ISLAND PARK ID. As with the annual flood peaks, the daily flow durations highlight the relatively low energy nature of the system and illustrate how consistent flows are in the Caldera Reach. Approximately 95% of all days in the entire period of record have flow less than or equal to 1,500 cfs. This is not unusual for a spring-fed river, and it is one of the primary reasons that the channel morphology throughout the Caldera Reach changes so little through time. 3.2 HISTORICAL AERIAL PHOTOGRAPHY We collected and analyzed historical aerial photography of the Caldera Reach to understand historical ecological and geomorphic conditions and identify trajectories of geomorphic change along the Caldera Reach. The historical aerial photography database consists of photo sets from 1953, 1959, 1967, 1972, 1973, 1987, 1988, 1992, 1995, 2004, and 2009 (Table 3). We orthorectified and compiled these images in the project GIS. 13

22 TABLE 3. HISTORICAL AERIAL PHOTOGRAPH DATES, FORMATS, EXTENT OF COVERAGE, AND APPROXIMATE DISCHARGE AT THE TIME OF THE PHOTO Date Format Coverage Discharge 7/19/1953 B/W Complete 1,480 7/19/1959 B/W Complete 2,080 7/11/1967 B/W Partial 1,201 7/28/1972 Color Partial 1,277 9/27/1973 Color Complete 872 8/31/1987 Color Complete Color IR Partial 8/9/1992 B/W Complete 1,744 6/29/1995 Color Complete 1,644 7/24/2004 Color Complete 1,479 6/24/2009 Color Complete 767 As expected for a relatively low energy, spring-fed river, we observe very little change in channel morphology between 1953 and Figures 8 and 9 are aerial photograph series of the Henrys Fork at Big Bend between 1953 and The red polygons on each photo indicate the approximate position of the islands in 1959 (taken at the highest discharge of any photo in the series) for comparison. Comparison of the island locations between the series of aerial photographs shows that the basic shape and size of the channel itself, as well as the islands in this reach, have changed very little over 60 years, with nearly all of the observed change likely a result of small errors in historical aerial photograph georectification and differences in streamflow between each photo. 14

23 FIGURE 8. HISTORICAL AERIAL PHOTOGRAPHS FROM 1953, 1973, 1987, AND 1992 THE RED PLOYGONS INDICATE THE POSITION OF THE ISLANDS IN

24 FIGURE 9. HISTORICAL AERIAL PHOTOGRAPHS FROM 1995, 2004, AND 2009 THE RED PLOYGONS INDICATE THE POSITION OF THE ISLANDS IN

25 While changes in channel morphology between 1953 and 2009 appeared to be extremely small, we were able to determine the following trends in channel morphology: Several of the smaller islands in the southern portion of the channel shown in the photographs have decreased in size or disappeared between 1953, 1959, and These islands tend to be on the outside of the bend. This disappearance cannot be explained by variations in discharge (i.e. higher stages inundating the islands) because the polygons used to compare the photo sets are drawn from the 1959 aerial photograph, which was taken when the flow in the Henrys Fork was higher than in any other aerial photograph series. Thus, we assume that the island features eroded during this period. The aerial photo sequence indicates a relatively stable channel from 1973 to 2009, with no observable changes in morphology. The lack of noticeable channel widening, lateral migration, or planform change suggests that any changes in channel morphology are occurring at a slow rate and/or a small scale. 3.3 CHANNEL GEOMETRY We used a survey grade RTK GPS system to survey channel geometry throughout the project area. Figure 10 shows the locations of all surveyed channel cross sections. We identified four general reach types in the study area with distinct channel geometry: 1) plain bed, 2) bend, 3) constricted chute, and 4) island. Figures show basic dimensions and features of channel geometry in each reach type. In general, plain bed reaches had uniform geometry from bank to bank, bend reaches were slightly deeper at the outside of the bend, constricted reaches were deeper in between the confining channel elements, and island reaches had undulating channel bed conditions. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 17

26 FIGURE 10. SURVEYED CHANNEL CROSS SECTION LOCATIONS SHOWING REPRESENATIVE CROSS SECTIONS FROM EACH REACH TYPE. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 18

27 Elevation (ft) Cross-Sectional Distance (ft) FIGURE 11. TYPICAL PLAIN BED CHANNEL GEOMETRY. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 19

28 Elevation (ft) Cross-Sectional Distance (ft) FIGURE 12. TYPICAL BEND CHANNEL GEOMETRY. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 20

29 Elevation (ft) Cross-Sectional Distance (ft) FIGURE 13. TYPICAL CONSTRICTED CHUTE CHANNEL GEOMETRY. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 21

30 Elevation (ft) Cross-Sectional Distance (ft) FIGURE 14. TYPICAL ISLAND CHANNEL GEOMETRY. 3.4 CHANNEL BED SEDIMENTS We assessed bed sediment characteristics in the Caldera Reach to determine current patterns of sediment distribution, deposition, and erosion, sediment transport potential, and aquatic habitat conditions for fish species in these areas. We used three different methods to characterize bed sediments: 1) facies mapping, 2) pebble counts, and 3) bulk samples. Working in close collaboration with the Henrys Fork Foundation, we collected sediment samples in the field between May 17, 2010 and May 21, 2010, in the Last Chance, Railroad Ranch, and Harriman East sections of the Henrys Fork. Specific methods of data collection and analysis are provided in more detail in the subsections below. FACIES MAPPING Facies are homogeneous units of channel bed material (Buffington and Montgomery, 1999). Detailed facies maps differentiate different populations of bed material (bedrock, cobble, gravel, sand, and silt) across the channel bed. We created detailed facies maps for the Henrys Fork channel to inform hydraulic modeling and to develop a baseline of the bed sediment composition for comparison with future bed sediment composition. We completed the channel bed assessment between May 17, 2010 and May 28, 2010 when the daily average discharge ranged from 529 cfs to 650 cfs at the Henrys Fork near Island Park, Idaho gage. We floated the Last Chance, Railroad Ranch, CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 22

31 and Harriman East reaches of the Henrys Fork, and identified sediments visually or by probing the channel bed with a steel rebar rod when depths were too great for direct visual observation. Different bed material provides a distinctive resistance and sound when probed with steel rebar, and the resistance and sound of different bed material was calibrated by probing the channel margins where bed conditions could be directly observed. Based on continuous direct observation or probing of the channel bed, unique facies were classified as follows (Table 4): TABLE 4. SEDIMENT SIZE CLASSIFICATIONS USED IN HENRYS FORK FACIES MAPPING COASER, LARGER SEDIMENTS FINER, SMALLER SEDIMENTS Bedrock Gravel/ Bedrock Sand/ Bedrock Silt/ Bedrock Very Coarse Gravel Medium Gravel Gravel Gravel/ Sand Sand/ Gravel Gravel/ Sand Gravel/ Bedrock Sand/ Gravel Sand Sand/ Silt Silt We mapped the results of the facies mapping on field base maps and then digitized them to produce a continuous facies map for the entire study area (Figure 15). Of the mapped reach, the gravel facies composed 61% of the channel area, sand composed 28% of the area, bedrock composed 7% of the area, and silt composed the remaining 4% of the study area. In general, gravel deposits were rounded and appeared to have been fluvially transported. Bedrock outcrops cross the channel at several locations, but are limited in spatial extent. Silt dominated facies are primarily located on the channel margins, but the largest silt dominated facies are located at Millionaire s Pool and immediately upstream. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 23

32 FIGURE 15. CHANNEL BED SEDIMENT FACIES MAP OF THE LAST CHANCE, RAILROAD REACH, AND HARRIMAN EAST REACHES OF THE HENRYS FORK. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 24

33 PEBBLE COUNTS We also conducted Wolman pebble counts (Wolman 1954) to characterize channel bed surface sediment grain sizes along 14 transects in the Last Chance and Railroad Ranch reaches of the Henrys Fork (Figure 16). The Wolman pebble count method involves measuring the diameter of the intermediate axis of 100 randomly selected stones along a given transect. We used the pebble count data to quantify the coarse bed sediment matrix that would need to be mobilized in a given reach to mobilize the fine sediments that are the focus of this study. The pebble count data was used directly in the hydraulic and sediment transport modeling described in the following sections. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 25

34 FIGURE 16. LOCATION OF PEBBLE COUNTS AND BULK SAMPLES ALONG THE HENRYS FORK. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 26

35 The results of the pebble count analyses are typically expressed in terms of a median diameter (i.e. the DR50R) of the grain size distribution. Table 5 summarizes all of the pebble counts collected for this study. Other than the 205mm D R50R collected in the chute at the log jam, D R50RR Rvalues range from 14 mm to 57.5 mm (medium gravel to very coarse gravel). Figures showing the cumulative particle size distributions and histograms for all pebble counts and a summary table of the cumulative distribution, D 16, D 50, and D 84 are provided in Appendix A. TABLE 5. PEBBLE COUNT SAMPLE SITE, LOCATION, AND MEDIAN GRAIN SIZE. Median Grain Pebble Count Sample Site Transect (Cross Section Station) Location Size (D50) - Millimeters Median Grain Size (D50) Particle Size Class HFPC 1 0 Entire transect 31.5 Coarse gravel Center 28.5 Coarse gravel HFPC Right bank 19.2 Coarse gravel Left bank 40.0 Very coarse gravel HFPC Center 22.5 Coarse gravel Right bank 57.5 Very coarse gravel HFPC Right bank 41.0 Very coarse gravel HFPC Entire transect 23.2 Coarse gravel HFPC Left bank chute Large cobble HFPC Center 25.5 Coarse gravel 1100 Left bank 35.7 Very coarse gravel HFPC Left bank 28.7 Coarse gravel HFPC Right bank 20.3 Coarse gravel HFPC Left bank 16.7 Coarse gravel HFPC Right bank 24.8 Coarse gravel HFPC Left bank 24.0 Coarse gravel HFPC Entire transect 14.0 Medium gravel HFPC Entire transect 24.5 Coarse gravel BULK SAMPLES We collected bulk samples following the methodology described in McNeil and Ahnell (1964), although the actual sampling methods employed were slightly modified (e.g. we didn t use a tube in the sampler - rather the cylinder was open, we used different sieve sizes, and we didn t wait for suspended silts to settle when processing the sample). We sampled within eight different substrate types from the upstream boundary of Harriman Park to the Thurmon Creek confluence on May 20, 2010 (Table 6; Figure 16). We placed the 18 diameter open metal cylinder within the specified substrate type on the river bed away from the river or island margins, but not so deep as to fully submerge the sampler. We manually worked the cylinder into the substrate about six inches deep. Because the bed surface sediments were composed of coarse, embedded particles in sample locations 1-3, we removed large particles off the substrate surface prior to sampling. We dug down with scoops and neoprene gloves within the McNeil sampler to collect about a third to half of a fivegallon bucket of material (Figure 17). The sample was wet sieved and the mass of the different size materials determined with the volumetric method on June 18, CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 27

36 TABLE 6. HENRYS FORK CALDERA REACH BULK SAMPLING SITES. Bulk Sample Latitude Longitude Comments Site HFBS Very coarse gravel at HFPC11. Top layer removed. HFBS Coarse gravel at HFPC13. Top layer removed. HFBS Medium gravel at HFPC17. Top layer removed. HFBS Sand/gravel HFBS Silt. Sampled where bed is silty. HFBS Gravel/sand HFBS Sand. Sampled where bed is sandy and depth was workable. HFBS Silt/sand. Sampled where bed is silt and sand, and where depth was workable. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 28

37 FIGURE 17. BULK SAMPLER AND EXCAVATED MATERIAL. The results of the bulk sampling analysis are provided in Table 7 and Figure 18. TABLE 7. HENRYS FORK BULK SEDIMENT SAMPLE PERCENT VOLUME PER SEDIMENT SIZE CLASS (THE LARGEST SEDIMENT SIZE CLAST BY VOLUME IS HIGHLIGHTED AND BOLDED FOR EACH SAMPLE SITE). Sieve Size (Inches) Sieve Size (mm) Particle Diameter % of Particles Retained (% Sediment Volume for Each Size Class) Site #1 2.5 inch mm (cobble) 30.3% 20.3% 0.0% 0.0% 0.0% 5.8% 0.0% 0.0% 1.0 inch inch inch 6.35 # # # # # mm -> 63.4mm (coarse -> very coarse gravel) 12.7mm -> 25.3mm (medium -> coarse gravel) 6.35mm -> 12.6mm (fine -> medium gravel) 4.76mm -> 6.34mm (fine gravel) 2.38mm -> 4.75mm (very fine gravel -> fine gravel) 0.84mm -> 2.37mm (coarse sand -> very fine gravel) 0.21mm -> 0.83mm (fine sand -> coarse sand) 0.05mm -> 0.20mm (silt -> fine sand) Site #2 Site #3 Site #4 Site #5 Site #6 Site #7 Site #8 21.3% 30.0% 52.4% 0.7% 6.0% 15.2% 0.0% 0.0% 18.8% 16.2% 5.8% 6.1% 13.2% 32.0% 0.1% 0.0% 12.8% 12.9% 13.3% 8.2% 17.0% 24.3% 17.6% 0.0% 2.2% 2.1% 5.8% 5.3% 9.3% 6.3% 5.1% 0.0% 6.7% 6.9% 10.4% 17.0% 15.8% 9.9% 23.8% 0.2% 2.4% 4.6% 8.7% 24.9% 14.2% 4.1% 4.6% 69.6% 5.3% 6.9% 3.1% 35.7% 21.4% 2.1% 46.0% 28.5% 0.2% 0.1% 0.5% 2.1% 3.2% 0.3% 2.7% 1.6% CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 29

38 Percent of Sediment Volume for Each Size Class 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% Site #1 Site #2 Site #3 Site #4 Site #5 Site #6 Site #7 Site #8 0.0% Sediment Particle Size Larger Than (sieve size in mm) FIGURE 18. HENRYS FORK BULK SEDIMENT SAMPLE PERCENT VOLUME PER SEDIMENT SIZE CLASS FOR EACH SAMPLE SITE. CHANNEL BED SEDIMENT TRENDS AND DISTRIBUTION The distribution of bed sediments along this portion of the Henrys Fork is characterized by the following trends: - The gradual fining of bed materials in the downstream direction. The upper areas of the bed sediment sampling reach from the Blue Springs Creek confluence through the Big Bend, as shown in the facies mapping (Figure 15), pebble count sample sites HFPC 1 13, and bulk sample sites HFBS 1-3, are predominately medium to coarse gravel, fairly evenly distributed across the channel. However, the lower sections of the bed sediment sampling reach, from Big Bend to the confluence of Fish Creek, show more variability in channel bed sediment size and distribution, with areas of sand and silt interspersed with fine, medium, and coarse gravels, as shown in the facies mapping, pebble count sample site HFPC 14, and bulk sample sites HFBS Variations in bed sediments occur laterally (across the channel) as well as longitudinally (down the channel profile) according to differences in channel geometry and flow velocities and shear stresses. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 30

39 - Areas of fine sediments (sand and very fine gravels) occur in isolated patches between Big Bend and the confluence of Fish Creek, primarily at the tail end of Big Bend, and the tail end of Millionaire s Pool (Figure 19). FIGURE 19. FINE SEDIMENTS IN THE CHANNEL BED. This channel bed sediment data provides a baseline dataset to allow sediment mobility analyses and modeling, as well as comparisons with subsequent monitoring efforts associated with flushing flow studies. 3.5 HYDRAULIC AND SEDIMENT TRANSPORT MODELING We developed both 1-dimensional and 2-dimensional hydraulic models of the Henrys Fork Caldera Reach to understand flow and sediment transport characteristics in the study reach for flow conditions that have not or cannot be measured in the field. The primary purpose of our hydraulic modeling investigation was to identify flow thresholds above which channel bed sediment would be mobilized with the current channel geometry and possible modified channel geometry (i.e. creation of islands to confine flow and facilitate sediment mobilization at lower flows). We used HEC-RAS, a simple, robust, and commonly used one-dimensional model produced by the United States Army Corps of Engineers and SRH 2-D, a more detailed, complex, two-dimensional model produced by the United States Bureau of Reclamation to take advantage of the strengths of both tools in the context of the objective of this study. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 31

40 APPROACH We developed and implemented the hydraulic models for this project to accomplish the following objectives: Predict water surface elevations, velocities, and bed sediment transport characteristics in the Caldera Reach for a range of possible flow events. Determine a peak flow release that could be implemented at Island Park Dam upstream to mobilize accumulated fine sediments in the study reach, particularly immediately downstream of Big Bend and Millionaire s Pool. Determine if and what channel geometry changes could be implemented to further improve sediment transport characteristics relative to rainbow trout habitat and desired ecosystem function. Hydraulic modeling generally consists of the following steps: 1. Define the physical boundaries of the model and develop the channel geometry or topography. 2. Establish boundary conditions for each flow regime of interest. 3. Run the model, and calibrate it to known flow conditions if possible. 4. Evaluate results and re-run as necessary to obtain the best simulation solutions possible. MODELS HEC-RAS HEC-RAS is a one-dimensional hydraulics model that calculates water surface elevation, velocity, and other hydraulic parameters for an open channel. HEC-RAS requires definition of the geometry of the channel being analyzed by representative cross-sectional profiles throughout the length of the project reach. Hydraulic parameters are calculated at each cross-section. One-dimensional models like HEC-RAS typically calculate velocity and other hydraulic parameters as an average across the width of the channel and with the depth of flow. We used HEC-RAS to develop a rating curve (relationship between flow and water surface elevation) for the Caldera Reach of the Henrys Fork and to validate results from the 2-dimensional SRH 2-D hydraulic model. The validation approach is described later in this document. SRH 2-D SRH 2-D is a two-dimensional hydrodynamic model that calculates water surface elevation, velocity, and other hydraulic parameters for a river channel at each node in a user-created model mesh. The model mesh is a network of nodes connected by triangles or quadrilaterals (elements) that is drawn by the user throughout the extents of the river reach being modeled. SRH 2-D requires a digital elevation model (DEM) to define the topography of the model. We used SRH 2-D for most of the modeling evaluations in this study. We calibrated the SRH-2D model to measured water surface elevations and further validated model performance with comparisons to the HEC-RAS model results. The calibration and validation approaches are described later in this document CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 32

41 MODEL CONSTRUCTION AND SET UP Topography We developed both the HEC-RAS and the SRH-2D models using the topographic survey data described above. The HEC-RAS model used all 85 surveyed cross sections. While not initially scoped as part of this study, we realized that the dense coverage of cross sectional data provided an excellent data set from which to develop the topography needed for a 2-D model, which would represent flow complexities in and around islands and other channel forms much more realistically than a 1-D model. We used manual interpolation techniques to construct a DEM of the study reach based on the surveyed cross-sections and available aerial photography. This required creation of topographic data points in areas between surveyed cross-sections where no topographic data existed and avoided the expense of a more detailed topographic survey effort. Boundary Conditions Both HEC-RAS and SRH 2-D require user input of upstream and downstream boundary conditions to perform all runs. Typically, the upstream boundary condition is the desired volumetric flow rate, and the downstream boundary condition is a known water surface elevation at the flow rate of interest. When the river under analysis has a stream gauge or an established rating curve at the downstream end of the model, both boundary conditions for a variety of flows are simple to develop. For this study, no nearby gauge exists, nor does a rating curve for the downstream end of the project reach. However, we collected water surface elevation data along the full length of the project reach during the topographic survey and determined the flow in the project reach at the time of the survey to be approximately 850 cfs (calculated by summing releases from Island Park Dam and flow in the Buffalo River). This provided the necessary pair of flow and water surface elevation for initial runs in both HEC-RAS and SRH 2-D. We performed model runs at a variety of flows in HEC-RAS using its "normal depth" downstream boundary condition setting. This setting enables model runs to be completed without a known downstream water surface elevation boundary condition based on the assumption that flow is at normal depth (i.e. the depth of flow in a channel when the slope of the water surface and channel bottom is the same and the water depth remains constant). We are confident that the hydraulic characteristics at the downstream end of the study area are well represented by the normal depth assumption. Results from the HEC-RAS model runs provided the water surface elevation at the downstream end of the project reach for use in constructing a rating curve that we subsequently used as a downstream boundary condition for the SRH 2-D model runs. Calibration, Validation, and Sensitivity Testing Numerical models that calculate or predict natural behavior are subject to error from a variety of sources including input data measurement and choice of model settings and other parameters. We completed several procedures to verify that the calculations and predictions made by SRH 2-D were appropriate. These included calibration against known hydraulic conditions, validation between the two hydraulic models used, and testing to determine the models sensitivity to various input parameters. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 33

42 Calibration Calibration of a hydrodynamic model to measured conditions assures that the model assumptions, data inputs, and settings are appropriate. We used the complete water surface profile of the study reach collected at a flow of approximately 850 cfs to calibrate both the HEC-RAS and SRH 2-D models by running both models at 850 cfs and then assessing how closely the model results matched the known conditions in the study reach. We ran the models iteratively and modified the Manning s "N" parameter, which describes the roughness of the channel bed, to calibrate both models. For both the HEC-RAS and SRH 2-D models, a Manning's "N" of produced the most similar water surface profile to the measured data. Figure 20 shows the graphical comparison of water surface profiles produced by each of the two models and that measured in the field Calibration of Models 850 cfs 6150 Water Surface Elevation (ft) cfs Observed HEC-RAS 850 cfs SRH-2D 850cfs Longitudinal River Distance (ft) 4TFIGURE 20. RESULTS FROM BOTH MODELS COMPARED AGAINST OBSERVATIONS OF ACTUAL WATER SURFACE ELEVATIONS AT 850 CFS. Both models matched observed water surface profiles quite closely between river station zero and approximately 20,000 feet downstream. After 20,000 feet, there are numerous island that result in slight differences between how downstream river distance is measured by the two hydraulic models. This results in a "shorter" profile in the HEC-RAS model results. This discrepancy becomes greater due to a large island approximately 30,000 feet downstream from station zero. This discrepancy can be seen as a gap between the water surface profiles in the plot; however, the predictions of water surface elevations themselves are well matched in real world space. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 34

43 Validation Because measured water surface profiles were only available for 850 cfs, the models could not be calibrated for other flows. Therefore, we validated the SRH 2-D model by comparing results for a variety of flows against HEC-RAS results of the same flows. Figures 21, 22, and 23 show results of validation testing for 350, 1000, and 3500 cfs. In all three cases, water surface elevation profiles match well. As described above, a difference in the calculation of downstream distance by the two models result in an offset between model results after approximately 20,000 feet downstream that becomes greater at approximately 30,000 feet downstream Validation of SRH 2-D Model 350 cfs 6160 SRH2D 350 cfs HEC-RAS 350cfs Water Surface Elevation (ft) Downstream Distance (ft) 4TFIGURE 21. COMPARISON OF WATER SURFACE ELEVATIONS PREDICTED BY BOTH MODELS AT 350 CFS. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 35

44 6180 Validation of SRH 2-D Model 1000 cfs 6160 SRH2D 1000 cfs HEC-RAS 1000 cfs Water Surface Elevation (ft) Downstream Distance (ft) 4TFIGURE 22. COMPARISON OF WATER SURFACE ELEVATIONS PREDICTED BY BOTH MODELS AT 1000 CFS Validation of SRH 2-D Model 3500 cfs 6160 HEC-RAS 3500 cfs SRH2D 3500 cfs Water Surface Elevation (ft) Downstream Distance (ft) 4TFIGURE 23. COMPARISON OF WATER SURFACE ELEVATIONS PREDICTED BY BOTH MODELS AT 3500 CFS. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 36

45 Sensitivity Testing As a final investigation of the validity of the SRH 2-D model results, we tested the sensitivity of model output to Manning s N (input parameter describing the roughness of the channel bed) and the downstream boundary condition (a set water surface elevation provided from HEC-RAS model runs). Sensitivity testing on Manning's N, shown in Figure 24, evaluates how much error is likely introduced to the model predictions based on improper selection of this model input parameter. We selected a value of because it produced a water surface profile most similar to that measured in the field at a flow of 850 cfs. Figure 24 compares this setting with a model run for 850 cfs with a Manning s N value of This corresponds to a higher roughness value, which in turn produces a slightly higher water surface. For most of the project reach, the difference between the water surface predicted in the two model runs is approximately 2 inches; however, in the downstream 10,000 feet of the project reach the difference varies between 4 and 6 inches SRH-2D Sensitivity Manning's N cfs 6150 Water Surface Elevation (ft) Manning's N Manning's N Downstream Distance (ft) 4TFIGURE 24. COMPARISON OF WATER SURFACE ELEVATIONS PREDICTED BY SRH 2-D AT 850 CFS FOR TWO VALUES OF MANNING S N (0.035 AND 0.045)4T Sensitivity testing for the downstream boundary condition is shown in Figure 25. For most of the model runs performed as part of this analysis, the downstream boundary condition was determined by that predicted by HEC-RAS for model runs at the same flow. For this reason, any potential error in the HEC-RAS model may be transferred to SRH 2-D simulations if SRH 2-D is found to be sensitive to the downstream boundary condition. As can be seen in Figure 6, SRH 2-D predicts an identical water surface for all but the downstream 4000 feet of the project reach for two model runs with a 3.3 foot (1 m) difference in set water surface elevation. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 37

46 6160 SRH-2D Sensitivity Downstream Boundary Condition 6150 Water Surface Elevation (ft) m B.C. 1858m B.C Downstream Distance (ft) FIGURE 25. COMPARISON OF WATER SURFACE ELEVATIONS PREDICTED BY SRH 2-D AT 850 CFS FOR TWO VALUES OF DOWNSTREAM BOUNDARY CONDITION (1857 AND 1858 M). Based on the results of calibration with measured hydraulic conditions, validation between two different modeling systems, and an analysis of model sensitivity to various input parameters, we determined that the model predictions from SRH 2-D would produce reasonable results for hydraulic and sediment transport analyses of the study area. MODEL RESULTS Bed Mobility SRH 2-D predicts bed shear stress, which is a measure of the tractive force of the flowing water on the channel bed material. This is an important factor for transport of sediment in a channel, because when the tractive force of water exceeds the gravitational and cohesive forces retaining sediment on the bed, bed load transport begins to occur. This condition is known as incipient motion and the water s tractive force at which it occurs is called critical shear. The critical shear varies with bed material type; the larger or more cohesive a sediment type, the higher is its associated critical shear. We developed bed mobility maps for the study reach of Henrys Fork based on predictions of bed shear stress from SRH 2-D overlain on facies map described above. Table 8 summarizes the critical shear values we used for each bed material type (Fischenich 2001), with the exception of "Land, which we derived from published values for grasses (Carroll and Theisen 1990), and "Bedrock,"which we assigned a sufficiently high value to eliminate potential for mobility. We calculated mobility as the shear stress predicted by the SRH-2D model for a given facies divided by the critical shear of the facies from Table 8. CIN/120709HENRYSFORKHYDROGEOMORPHREPORTFINAL 38

47 Mobility of 1 is the critical shear, where the bed should be mobilized. Because the critical shear varies with topography and bed material size over the bed, we use a range of 20% above and below the critical shear to classify the bed as stable, starting to mobilize, and completely mobile. In the following mobility maps, we classified the bed as stable if the mobility is less than 0.80 (green dots), starting to mobilize from 0.80 to 1.20 (yellow dots), and fully mobilized at values greater than 1.20 (red dots). TABLE 8. CRITICAL SHEAR STRESS VALUES FOR DIFFERENT SEDIMENT TYPES. Bed Type Critical Shear (N/m2) (lbs/in 2 ) Bedrock Gravel Gravel/Bedrock Gravel/Sand Land Sand Sand/Bedrock Sand/Gravel Sand/Silt Very Coarse Gravel Adapted from Fischenich 2001 We modeled bed mobility for the entire study reach and present the results of modeling at two key locations (Figure 26). We selected the Big Bend and Millionaire s Pool reaches because our facies mapping showed concentrations of fine sediment in those two areas, and because of the importance of the Millionaire s Pool as fish habitat and a preferred angling location. We selected two flows that bracket the expected and modeled range of flows in the proposed flushing flow hydrograph to illustrate the difference in bed mobility with discharge in the existing channel. 350 cfs is close to the base flow condition and 3,500 cfs is slightly above the proposed peak discharge. Additionally, we modeled the same reaches at 350 cfs and 3,500 cfs under a scenario where additional islands have been constructed to further concentrate the flow in the channel to increase channel bed shear stress. 39

48 FIGURE 26. PRIORITY AREAS FOR SEDIMENT MOBILITY ANALYSIS. Mobility Modeling Results at 350 cfs Existing Channel Under approximate base flow conditions, the bed mobility modeling for the Big Bend reach (Figure 27) shows only one small area near incipient motion. In addition, our modeling shows that portions of the channel are either not deep enough to mobilize sediment or are not wetted at 350 cfs. Similar results are shown in Figure 28 at Millionaire s Pool. At the Millionaire s Pool reach there are two small areas where mobility approaches incipient motion and one small area where the bed is mobilized. 40

49 FIGURE 27. BIG BEND RESULTS AT 350 CFS, EXISTING CHANNEL GEOMETRY. RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. FIGURE 28. MILLIONAIRE S POOL RESULTS AT 3500 CFS, EXISTING CHANNEL GEOMETRY. RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. 41

50 Mobility Modeling Results at 3,500 cfs Existing Channel Mobility modeling with existing channel geometry at 3,500 cfs shows an increase in bed mobility at both sites (Figure 29 and 30). At the Big Bend reach, our modeling results show bed mobilization in the narrower portions of the reach at the entry and exit of the bend and at the narrow channels on both sides of the island at the center of the bend. In the wider sections of the reach, our modeling shows the bed is stable. FIGURE 29. BIG BEND RESULTS AT 3500 CFS, EXISTING CHANNEL GEOMETRY. RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. At the Millionaire s Pool Reach, our modeling shows a larger portion of the bed is mobile at 3,500 cfs, but a smaller portion of the reach is mobilized compared to the Big Bend Reach at the same discharge. Bed mobility is again located in areas where the channel width is narrow, at the downstream extent of the reach and in a few of the narrow channels around mid-channel islands. 42

51 FIGURE 30. MILLIONAIRE S POOL RESULTS AT 3500 CFS, EXISTING CHANNEL GEOMETRY. RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. Mobility Modeling Results at 350 cfs Constructed Islands We conducted additional modeling to see if constructing islands in the channel at both Big Bend and Millionaire s Pool would narrow the channel enough to concentrate flow sufficiently to mobilize the bed. Islands were built in the model with similar shapes and sizes as the existing islands in the channel. One island was inserted into the mobility model at Big Bend near the center of the bend, and two islands were inserted downstream of the Millionaire s Pool. Our model results show that at 350 cfs, the constructed islands have a small effect on bed mobility (Figure 31 and 32). In Figure 31 and 32, the islands are shown as the area without dots. Our modeling results from the island placement at Big Bend (Figure 31) shows that a backwater is created and the full channel and the upstream island are inundated when compared to the existing condition 350 cfs discharge (Figure 27). Four additional areas of incipent motion result from island construction at Big Bend. However, the areas of increased incipient motion are very small. At the Millionaire s Pool reach (Figure 32), there was no change in the area of incipient motion, but the location of incipient motion changed. One area of incipient motion was moved further downstream. 43

52 FIGURE 31.BIG BEND RESULTS AT 350 CFS, CONSTRUCTED ISLAND CHANNEL GEOMETRY (AREA WITHOUT DOTS). RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. FIGURE 32. MILLIONAIRE S POOL RESULTS AT 350 CFS, CONSTRUCTED ISLAND CHANNEL GEOMETRY (AREAS WITHOUT DOTS). RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. 44

53 Mobility Modeling Results at 3,500 cfs Constructed Islands Next we modeled the impact of adding islands to the channel at 3,500 cfs at Big Bend and Millionaire s Pool to increase bed mobility. Bed mobility decreased at Big Bend when flows were increased to 3,500 cfs with the constructed island (Figure 32). Surprisingly, the constructed island in the model creates a backwater and reduces shear stress. Using the model to iterate changes in constructed island shape and elevation we could likely optimize the island geometry to increase bed mobility. In the Millionaire s Pool Reach, our addition of two islands in the model increased bed mobility (Figure 34). The constructed islands at Millionaire s Pool did not create a backwater but sufficiently narrowed the channel without creating an obstruction to flow and increased bed mobility. The result of the bed mobility modeling shows mobilization at 3,500 cfs with the existing channel geometry. We can increase mobility with constructed islands downstream of Millionaires Pool, but initial runs with constructed islands at Big Bend don t increase mobility. Additional model iterations would be required to improve size and placement of islands at Big Bend to optimize bed mobility. 45

54 FIGURE 33. BIG BEND RESULTS AT 3500 CFS, CONSTRUCTED ISLAND CHANNEL GEOMETRY (AREA WITHOUT DOTS). RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. FIGURE 34. MILLIONAIRE S POOL RESULTS AT 3500 CFS, CONSTRUCTED ISLAND CHANNEL GEOMETRY (AREAS WITHOUT DOTS). RED IS MOBILE. YELLOW IS NEAR INCIPIENT MOTION. GREEN IS NOT MOBILE. 46

55 4 PEAK FLOW RELEASE RECOMMENDATIONS As described in the preceding sections of this report, we performed detailed investigations of historical hydrology, historical geomorphic change, and existing channel sediment characteristics, and we developed a two dimensional hydraulic model that was applied to identify flows necessary to mobilize the bed sediments of the Henrys Fork in the Caldera Reach. These analyses provided the foundation for the development of a peak flow hydrograph that could be implemented to mobilize accumulated fine sediments in the channel, with the ultimate goals of improving habitat conditions that were impacted by the large release of fine sediment from Island Park Reservoir in These recommendations could also be used to improve management approaches for future fine sediment releases during reservoir drawdown. 4.1 PEAK FLOW RELEASE HYDROGRAPH The proposed peak flow hydrograph combines releases from Island Park Reservoir through both the power plant and the spillway, and the natural discharge from the Buffalo River. Discharge from the Buffalo River is expected to be about 200 cfs during the anticipated timeframe for a peak flow release (mid-april dependent on snowmelt and potential downstream flooding conditions). While ramping up and down to and from the peak flow, discharge would be held constant for sediment sampling. Plateaus in the hydrograph occur at 1,000, 2,000, and 2,500 cfs during the ramp up to the peak flow of 3,000, and at 2,750 and 2,500 cfs while ramping back down to the base flow. Ramping for the peak flow would begin in mid-april, and the peak would be maintained for one day. Ramping down to base flow will be completed one day later. Figure 35 illustrates the peak flow hydrograph and Table 9 lists the date, time, and discharge of sampling events developed for the April 2011 peak flow release that was cancelled just prior to implementation. 47

56 3,500 Peak Flow Hydrograph 3,000 2,500 Discharge (cfs) 2,000 1,500 1, /24/ :00 4/24/2011 6:00 4/24/2011 0:00 4/23/ :00 4/23/ :00 4/23/2011 6:00 4/23/2011 0:00 4/22/ :00 4/22/ :00 4/22/2011 6:00 4/22/2011 0:00 4/21/ :00 4/21/ :00 4/21/2011 6:00 4/21/2011 0:00 4/20/ :00 4/20/ :00 4/20/2011 6:00 4/20/2011 0:00 4/19/ :00 4/19/ :00 4/19/2011 6:00 4/19/2011 0:00 4/18/ :00 4/18/ :00 Date FIGURE 35. PROPOSED PEAK FLOW HYDROGRAPH. TABLE 9. DATE, TIME, AND DISCHARGE OF SAMPLING OR DISCHARGE EVENTS. Date and Time Combined Henrys Fork and Buffalo River Discharge (cfs) Sampling or Discharge Event 4/19/11 12:00 AM 300 Ramp up 4/19/11 7:00 AM 1,000 Big Bend first priority 4/19/11 11:00 AM 1,000 Millionaire's Pool first priority 4/19/11 3:00 PM 2,000 Big Bend first priority 4/19/11 7:00 PM 2,000 Millionaire's Pool first priority 4/20/11 7:00 AM 2,500 Big Bend first priority 4/20/11 9:00 AM 2,500 Big Bend second priority 4/20/11 11:00 AM 2,500 Big Bend third priority 4/20/11 3:00 PM 2,500 Millionaire's Pool first priority 48

57 Date and Time Combined Henrys Fork and Buffalo River Discharge (cfs) Sampling or Discharge Event 4/20/11 5:00 PM 2,500 Millionaire's Pool second priority 4/20/11 7:00 PM 2,500 Millionaire's Pool third priority 4/21/11 7:00 AM 3,000 Big Bend first priority 4/21/11 9:00 AM 3,000 Big Bend second priority 4/21/11 11:00 AM 3,000 Big Bend third priority 4/21/11 3:00 PM 3,000 Millionaire's Pool first priority 4/21/11 5:00 PM 3,000 Millionaire's Pool second priority 4/21/11 7:00 PM 3,000 Millionaire's Pool third priority 4/22/11 7:00 AM 3,000 Big Bend first priority 4/22/11 9:00 AM 3,000 Big Bend second priority 4/22/11 11:00 AM 3,000 Big Bend third priority 4/22/11 3:00 PM 3,000 Millionaire's Pool first priority 4/22/11 5:00 PM 3,000 Millionaire's Pool second priority 4/22/11 7:00 PM 3,000 Millionaire's Pool third priority 4/23/11 7:00 AM 2,750 Big Bend first priority 4/23/11 11:00 AM 2,750 Millionaire's Pool first priority 4/23/11 3:00 PM 2,500 Big Bend first priority 4/23/11 7:00 PM 2,500 Millionaire's Pool first priority 4/23/11 9:00 PM 2,500 Ramp down 4/24/11 5:00 AM 300 Base flow 4.2 FLUSHING FLOW SEDIMENT TRANSPORT MONITORING PLAN Through the development of a well-thought out and properly executed monitoring plan, we will be able to evaluate the peak flow release to refine our understanding of the hydraulics, sediment transport dynamics, and relationships between sediment, macrophyte communities, and channel morphology. We propose three primary objectives for monitoring sediment transport during the flushing flow event: 1. To determine the threshold of incipient motion for portions of the Henrys Fork channel bed in the Caldera reach; 49

58 2. To develop bedload and suspended sediment transport rating curves. Flows between approximately 1,000 cfs and 3,000 cfs in the Caldera reach (from releases between 800 cfs and 2,870 cfs from Island Park reservoir) will be used to validate and refine the 2-D hydraulic model of the area and to improve our understanding of sediment transport and macrophyte community dynamics in the area; 3. To mobilize fine sediments from the 1992 release from Island Park reservoir in specific locations within the Caldera reach that still appear to be impacted by fine sediment from that release. The sediment transport monitoring plan specifies monitoring locations, suspended sediment and bedload sampling methods, and flow velocity and discharge sampling methods. Figure 36 illustrates the proposed monitoring locations in plan view. The time required to conduct suspended and bedload samples is dependent on the difficultly in maintaining the sampling position in the channel and the amount of material collected in each sample. As a result, we identified three suspended and bedload sampling locations at Big Bend and Millionaire s Pool. At the Big Bend and Millionaire s Pool locations, the first priority sampling location would be conducted first. If time permits, the second and third priority transects would be sampled. Table 10 lists the proposed transect identification, location description, and monitoring method(s) that would be used at each transect. We propose using a range of sediment transport monitoring methods before, during, and after the peak flow release. In addition, we suggest that aquatic vegetation monitoring be conducted before and after the peak flow release at previously monitored transects that coincide with the sediment transport sampling transects proposed for this study. Sediment transport monitoring methods would include suspended and bedload sediment sampling, tracer gravel placements, and optionally, scour chain installations. 50

59 FIGURE 36. PLAN VIEW OF FLUSHING FLOW MONITORING LOCATIONS. TABLE 10. PROPOSED LOCATIONS FOR PEAK FLOW MONITORING. Bedload and Suspended Transect Sediment Sampling Scour Chains Tracers Vegetation Trout Hunter tracers only No Optional Yes No Big Bend first priority Yes Optional Yes No Big Bend second priority Yes Optional Yes Yes 51

60 Big Bend third priority Yes Optional Yes Yes Millionaire s Pool first priority Yes Optional Yes Yes Millionaire s Pool second priority Yes Optional Yes No Millionaire s Pool third priority Yes Optional Yes No SUSPENDED SEDIMENT SAMPLING Suspended sediment consists of particles transported downstream by being lifted into the water column (Dunne and Leopold 1978). We would use a handheld DH-48 depth integrated suspended sediment sampler (Figure 37) to collect water and suspended sediment. The sampler would be attached to a 3- foot-long wading rod with a 3 foot extension. The channel would be divided into verticals for sampling that have consistent velocities or bed and bank dimensions. We would lower and raise the sampler through the water column at a constant rate. Test samples would be conducted to determine the sampling period to fill the 16 ounce sampling bottle between two thirds full and completely full. Water and suspended sediment enters the sampler through an intake nozzle, and an exhaust tube allows air in the sample bottle to escape when displaced by water and suspended sediment. The sampler would be lowered through the water column with the wading rod perpendicular to the channel-bed surface to prevent capturing bedload in the sampling bottle. The angle of the sampler body allows samples to be collected to within 3.5 inches of the streambed (FISP, 2008). FIGURE 37. DH-48 SUSPENDED LOAD SAMPLER (FISP, 2008). BEDLOAD SEDIMENT SAMPLING Bedload sediment is sediment carried downstream by rolling or siltation on or near the streambed (Emmett, 1980). We would use a U.S. BLH-84 handheld bedload sampler (Figure 38) to collect bedload samples. The U.S. BLH-84 is a pressure-difference sampler with the same nozzle opening as the original Helley-Smith bedload sampler, but with a different area-expansion ratio. The Water Resources Division of the U.S. Geological Survey (USGS) endorses the use of the newer BLH-84 sampler and continues to 52

61 accept sample data collected by the Helley-Smith sampler (USGS, 1990; Edwards and Glysson, 1999). A micron mesh sample collection bag will be used with the sampler. Water and sediment flows through the sampler, and water and fine sediment pass through the mesh sample collection bag while coarse sediment is captured in the sample bag. The sampler would be attached to a 4- to 8-foot-long telescoping handle. The channel would be divided into verticals for sampling that had consistent velocities or bed or bank dimensions. The BLH-84 would be lowered to the channel bed, keeping the wading rod perpendicular to the channel-bed surface with the nozzle pointing into the flow. FIGURE 38. BLH-84 BEDLOAD SAMPLER. TRACERS PARTICLES Tracer particles can be used to provide information on the rate and direction of sediment transport and the flows at which particles are entrained (Kondolf and Piegay 2003). Gravel painted with safety red and yellow epoxy paint would be placed across the channel by Henrys Fork Foundation or NewFields staff. The painted gavels would be measured and the median axis measurement written on each tracer with a permanent pen. Tracers would be placed in the river following a transect perpindecular to flow (Figure 39). A native particle would be removed from the channel bed and the median axis measured and the station across the transect recorded. The location of the removed particle would be marked and a painted particle of similar shape and size would replace the removed particle. Tracer transects would be revisited after high flows, and if the painted particles have moved downstream, the distance moved would be recorded. 53

62 FIGURE 39. TRACER GRAVELS IN DEER CREEK, CALIFORNIA. SCOUR CHAINS (OPTIONAL) Scour chains are used to monitor the amount of scour and fill that occurs during peak flows. If this method is utilized, Henrys Fork Foundation staff would assemble scour chains and install them in priority areas of the river. The chain is anchored into the bed of the channel below the estimated maximum depth of scour. After installation the length of chain above the channel bed would be measured. After the high peak flow, the amount of exposed chain or the depth of burial would be measured by Henrys Fork Staff. If sediment is scoured from the bed the chain lays flat on the bed, forming a kink. If there is deposition of sediment the chain is buried with sediment, as illustrated in Figure 40 (Gordon et al. 2004). FIGURE 40. SCOUR CHAINS (FROM GORDON ET AL. 2004). PROPOSED HIGH PEAK FLOW MONITORING DATA POST-PROCESSING Suspended sediment samples would be composited for each transect for a given flow, and either processed by Henrys Fork Foundation staff or sent to a lab for processing and analysis. Bedload sediment samples would be dried and sieved by Henrys Fork Foundation staff or processed at a 54