Monitoring of Stream Flows and Playa Run-on in Dixie Valley for Water Years 2009, 2010 and 2011

Transcription

1 Monitoring of Stream Flows and Playa Run-on in Dixie Valley for Water Years 2009, 2010 and 2011 Prepared by: Interflow Hydrology, Inc., Truckee, CA & Mahannah & Associates, LLC, Reno, NV 1

2 Monitoring of Stream Flows and Playa Run-on in Dixie Valley for Water Years 2009, 2010 and 2011 Prepared by: Interflow Hydrology, Inc., Truckee, CA & Mahannah & Associates, LLC, Reno, NV January, 2013

3 Contents Executive Summary... 1 Introduction... 2 Physiography... 2 Section 1 - Field Reconnaissance Stream Channel Inspections and Determination of Active Channel Width Installation of Capacitance Rods... 6 Section 2 - Data Collection for Water Years Cap Rod Data Rating Curve Development at Gaged Streams Section 3 - Estimating Discharge at the Cap Rod Stations Discharge Estimates Based on Stage Data from Cap Rods Estimates of Annual Discharge at Cap Rod Gage Sites Water-Year Water-Year 2010 and Section 4 Discussion and Observations Contrasts in Water-Year Flows Estimating Total Playa Run-On Precipitation and run-off events Stream Channel Recharge Section 4 Program Challenges Section 5 - Field-Based Quality Control Measures Section 6 - References i

4 Figures Figure 1: Location map for Dixie Valley... 4 Figure 2: Channel inspection locations and capacitance rod locations near the playa periphery Figure 3: Capacitance rod installation locations, precipitation stations and basin geography, Dixie Valley... 7 Figure 4: Example of cross section data from field surveys at Cap Rod Site # Figure 5: Stage-discharge relationship for Freeman Creek (gage site #110) Figure 6: Stage-discharge relationship for Lower Horse Creek (gage site #107) Figure 7: Stage-discharge relationship for Horse Creek at Mountain Front (gage site #106), showing curve shift Figure 8: Stage-discharge relationship for Horse Creek at Mountain Front and WY2009 rating curve Figure 9: Stage-discharge relationship for Horse Creek at Mountain Front and WY rating curve Figure 10: Precipitation and flow by water year. *WY2009 was a partial water year for monitoring Figure 11: Spatial variability of observed flow to the Dixie Valley playa Figure 12: Regression of watershed area and measured annual flow between WY2009 WY2012 for eastern Dixie Valley playa gage sites 31, 40 56, 68, 73, 77, and Figure 13: Site #112 Cottonwood Creek comparison of 2009 pre & post flash flood cross-sections Figure 14a: Precipitation at USGS weather stations and the U.S. Navy Centroid Facility, Dixie Valley Figure 15a: Selected capacitance rod hydrographs and precipitation from the U.S. Navy Centroid Facility, Dixie Valley Figure 16: Graph of estimated peak flow recorded in Dixie Valley Wash at two stations Figure 17: Southern Dixie Valley and Dixie Wash gage stations Figure 18: Gaging station locations along Horse Creek and the Horse Creek alluvial fan, Dixie Valley Figure 19: Horse Creek hydrograph, partial WY Figure 20: Horse Creek hydrograph, WY Figure 21: Horse Creek hydrograph for WY Figure 22: Regression of stage data from the capacitance rod and pressure transducer at the Horse Creek at Mtn. Front station Figure 23: Comparison of crest stage gage and recorded stage at capacitance rod # Figure 24: Comparison of crest stage gage and recorded stage at capacitance rod # Figure 25: Comparison of crest stage gage and recorded stage at capacitance rod # Figure 26: Comparison of crest stage gage and recorded stage at capacitance rod # ii

5 Photographs Pg. Photo 1 Dixie Lake Playa and Brine 3 Photo 2 Cap Rod installation with Quad site #56 6 Photo 3 Cap Rod installation with Quad site #31 6 Photo 4 Cap Rod installation Horse Creek 8 Photo 5 Cap Rod installation Freeman Creek 8 Photo 6 Cottonwood canyon post-flood 24 Photo 7 Cottonwood between sites 112 and Photo 8 Cap rod on the east side of the playa 25 Photo 9 Spring Creek and cap rod Photo 10 Stillwater Range Drainages aerial view 34 Photo 11 Dixie Valley Fault aerial view looking north 34 A - Channel Reconnaissance and Survey Data B - Compiled Gage Data C - Computed Gage Discharge Plots Appendices iii

6 Executive Summary As part of a multi-year, multi-disciplinary study aimed at quantifying the water resources of Dixie Valley, Interflow Hydrology and Mahannah & Associates conducted stream channel reconnaissance and flow monitoring during water years (2009 data collection was for a partial water year). Twenty-three monitoring stations were operated and included several intermittent stream segments, a prominent perennial stream (Horse Creek), major ephemeral drainages entering Dixie Valley (Spring Creek and Dixie Wash), and fourteen channels that lead directly to the playa. Stations were surveyed to determine location, channel slope, and channel geometry, and equipped with continuous water height recorders. Water heights were used to compute flow at the gaging stations. The fourteen gages established to monitor surface water flow to the playa provided useful data on quantity, distribution, and variability of run-on to the playa for water years In the later half of 2009, observed run-on from the fourteen gaged drainages is estimated to be 370 AF; in 2010, 250AF; and in WY2011, 380 AF. The annual estimate of total playa run-on including contributions from ungaged drainages was similar for each water-year, being approximately 500 af/yr. Run-on to the Dixie Valley playa was observed to be dominated by inflows from Spring Creek, with estimated flows of 50 AF in WY 2009, 82 AF in WY 2010, and 234 AF in Additional flow to the playa occurred from Dixie Wash, which is estimated to be 105 AF in WY 2009, but less than 10 AF in WY2010 and WY2011. Shoshone Creek consistently provided between 21 and 64 AF to the playa during the study. Very little flow was observed from watersheds west of the playa. The intermittent stream flow gaging provided insight into recharge to the alluvial fan. Alluvial fan recharge along Horse Creek was observed to be approximately 200 AF/mile per year during the study period. Inflow to Dixie Valley from other hydrographic basins was observed to be dependent largely on severe weather events. Spring Creek at the Pleasant Valley boundary recorded flows of 52 AF in WY 2009; zero AF in WY 2010, and 203 AF in WY Inflow of surface water to Dixie Valley along Dixie Wash at Sand Dune Pass receives water from three upgradient hydrographic areas, and recorded an estimated inflow of 1334 AF in WY2010, zero AF in 2011, and an unquantified but small amount of flow in INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 1

7 Introduction Interflow Hydrology (Interflow) and Mahannah & Associates (Mahannah) have conducted a stream discharge data collection effort in Dixie Valley as a part of a multi-year evaluation of the water resources of the basin conducted under the direction of the Bureau of Reclamation (BOR) and on behalf of Churchill County, Nevada. The data collection effort has four primary components and objectives: 1. Obtain baseline stream flow data for a select number of perennial streams in the basin which produce run-off to the alluvial fans or valley floor, 2. Obtain data from ephemeral stream and run-off channels producing run-on to the Dixie Valley playa, 3. Collect data on flow infiltration along major stream channels on the alluvial fans and valley floor, 4. Gain insight to distribute recharge resulting from flow losses across the alluvial fans and along valley floor major stream channels. The following sections summarize data collection and interpretations, with particular emphasis on estimating playa run-on, for water-years 2009, 2010 and Physiography Dixie Valley is located east of Fallon, Nevada in the Basin and Range physiographic province. Several basins proximal to Dixie Valley contribute some degree of surface and groundwater flow. These basins are Fairview Valley, Jersey Valley, Pleasant Valley, Cowkick, Stingaree, and Eastgate Valleys. Collectively these basins form the Dixie Valley Flow System (Figure 1). Dixie Valley is an internally drained basin that is flanked on its western side by the Stillwater Range and on its eastern side by the Clan Alpine mountains. The basin floor is typically arid and consists of coalescing alluvial fans, and a relatively flat valley bottom. The west-central portion of the basin contains a playa that is periodically inundated by a brine pond (Photo 1). This area is surrounded by phreatophytic vegetation that generally becomes less dense with increased distance from the playa. Around the playa area, ephemeral stream channels, some with culverts where they cross roads, drain the surrounding fans and flat laying terrain and provide pathways for surface water run-on to the playa surface. The contribution of surface water run-on to the playa water balance has been largely unknown, and may be an important factor in both the water and salt budget for the playa area. In addition, several intermittent and perennial streams are located in Dixie Valley. Streamflow is rarely observed far beyond the mountainous portion of the basin. Total stream flow decreases as the creeks exit the mountain block and flow infiltrates into the alluvial fans. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 2

8 Photo 1: Dixie Valley playa & brine pond viewed to the west Stillwater Range in background - 4/21/09. Section 1 - Field Reconnaissance 1.1- Stream Channel Inspections and Determination of Active Channel Width Field crews traveled the perimeter of the playa in February 2009 to observe and document general conditions of the more substantial ephemeral channels capable of potentially producing run-on to the playa. Field work included measuring active channel width (ACW) as defined by Hedman and Osterkamp (1982), recording locations of channels with a hand-held GPS, photo documentation of channel conditions, and recording notes on general channel characteristics and presence or absence of flow. Conditions at approximately ninety channel locations (Figure 2) were recorded and summarized in Appendix A spreadsheets. ACWs were measured for a total of 66 channels, with values ranging from 1 foot to 18 feet with an average width of 2.4 ft. Stream channels on the west side of the Dixie Valley playa, originating from the Stillwater Range, are channelized into a road-side ditch on the west side of State Highway 121, with flows crossing beneath the road in a sequence of storm culverts. Culvert sizes and conditions were recorded, and ACW was recorded for channels below the culverts. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 3

9 Figure 1: Location map for Dixie Valley INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 4

10 Figure 2: Channel inspection locations and capacitance rod locations near the playa periphery. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 5

11 1.2 - Installation of Capacitance Rods TruTrack capacitance rods ("cap" rods) were deployed at selected gaging locations to record the presence or absence of flow and the depth of flow when flow was present. Capacitance rods measure changes in the ability of the instrument to store an electrical charge that result from the pronounced difference in chargeability between wet and dry conditions with a reported water level detection accuracy of < 1mm. Recording intervals were programmed at 15 or 60 minutes with data stored internally. Cap rod data can be used to determine the presence of flow and depth of flow (stage), from which a determination of flow quantity can be made using stage/discharge relationships. Between March and May of 2009, twenty three (23) cap rods were deployed throughout Dixie Valley (Figure 3). Sites selected fall into four general categories, those adjacent to the playa edge (twelve gages installed), those at mountain front streams (4 gages installed), gages along the two major ephemeral washes in the valley, Dixie Wash and Spring Creek wash (four gages installed), and gages on the lower portions of the alluvial fans down gradient from mountain-front gage sites (two gages installed). Locations of all gages with project site ID numbers, are shown on Figures 2 and 3 and typical playa cap rod installations are shown in Photographs 2 and 3. Topographic surveying was conducted at the gage sites using a survey-grade level and rod. At each gage site, surveying included a detailed cross section transect perpendicular to the channel from upper bank edge to edge. A transect of the longitudinal gradient or slope of the low-flow channel was also surveyed. An example transect developed from the survey data is presented as Figure 4, and additional survey data and transects are presented in Appendix A spreadsheets. To test the accuracy of the cap rod data collected as compared with more traditional stage recorders using a pressure transducer, the Horse Creek at Mountain Front site (#106) was additionally equipped with a Global Water WL400 pressure transducer. The data logger/transducer assembly, with 0 to 3 ft range, and 0.1% accuracy, was programmed to record data at 15 minute intervals and compared favorably with the cap rod data. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 6

12 Figure 3: Capacitance rod installation locations, precipitation stations and basin geography, Dixie Valley INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 7

13 CAP ROD RIGHT BANK Relative Elevation, Feet LEFT BANK RECENT FLOW LINE RECENT FLOWLINE Photo 2: Site #56 3/12/10 Photo 3: Site# 31 3/12/ Distance, Feet Figure 4: Example of cross section data from field surveys at Cap Rod Site # 56 Gaging sites were visited regularly to acquire instantaneous stream discharge measurements using standard current meter methods, and to inspect and download data from the recording units. For the mountain front stream gaging sites, the instantaneous measurements have been used to develop stage discharge rating curves (Section 3.2). Mountain front gage sites at Horse Creek (site 106) and Freeman Creek (site 110) are shown in Photographs 4 and 5. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 8

14 Photo 4: Site #106 Horse Cr. Mtn Front (5/14/09) Photo 5: Site# 110 Freeman Creek Mtn. Front (5/14/09) Section 2 - Data Collection for Water Years Cap Rod Data Twenty of the twenty-three cap rods deployed in 2009 produced useable data. One cap rod was washed away during a flash flood event on the 1 st of June, 2009 (Cottonwood Creek, site 112), one did not record any events (site 103, Stillwater drainage, double culvert) while a third did not capture flow in what appeared to be the obvious main channel (site 87, Dixie Wash). On the 26 st of August 2009, the site 87 gage was moved to site 86 which appears to be the primary active channel of Dixie Valley Wash. However, after relocating the cap rod gage to site 86, it was determined that significant flow from Dixie Wash was escaping from the "main" channel at an upgradient location, and the gage at site 86 should not be considered for representing all Dixie Wash flow discharging to the playa. During Water Year 2009 some data were lost due to the cap rod s memory reaching full capacity. Changes were made to reduce the number of parameters recorded (e.g. air temperature was removed) to increase effective memory capacity and reduce the chance of data loss. This effort proved very successful and during WY 2010 and 2011 the data gaps were significantly reduced. Even with this improved efficiency, data from cap rod 115 were lost due to a failure of computer hardware. Tables 1 and 2 summarize the meta-data for the cap rod gage locations and periods of effective data collection. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 9

15 Table 1: Cap Rod metadata, coordinates in UTM NAD 83. Site ID Number Gage Name Easting (m) Northing (m) Elev. (ft amsl) Date Deployed 91 Unnamed playa culvert , Unnamed playa culvert , Unnamed playa culvert , Spring playa , Shoshone playa , Bernice playa , Unnamed playa channel , Deer Lodge playa , Unnamed playa channel , Unnamed playa channel , Unnamed playa channel , Dixie Valley Wash , Dixie Valley Wash Playa , Double HDPE Culverts , Horse Mtn Front , Lower Horse Creek , Dixie V. Sand Dune Pass , Freeman Mtn. Front , Cottonwood Mtn. Front , Lower Cottonwood Cr , Shoshone Cr. Below Shoshone Meadows Spring Pleasant V. Sub-Basin Bdy , , Cow/Deep Mtn. Front , Dixie Valley Box Clvt. On SR , INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 10

16 Table 2: Period of record and recorded flow from cap rods, WY2009 WY Site ID No. Gage Name Days of Record, WY2009 Days of Record, WY2010 Days of Record, WY Unnamed playa culvert Spring playa Shoshone playa Bernice playa Unnamed playa channel Deer Lodge playa Unnamed playa channel Unnamed playa channel Unnamed playa channel Dixie Valley playa - primary channel Dixie Valley playa - secondary channel* Unnamed playa culvert Unnamed playa culvert Unnamed playa culvert Horse Mountain Front Lower Horse Creek Dixie V. Sand Dune Pass Freeman Mountain Front Cottonwood mountain front** Lower Cottonwood Cr Shoshone Cr. Below Shoshone Meadows Spring Pleasant V. Sub-Basin Bdy Cow/Deep Mtn. Front Dixie Valley Box Clvt. On SR * = Cap Rod 87 was decommissioned and moved to Site 86 ** = Cap Rod 112 was lost in a flood event INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 11

17 Flow, in cfs Rating Curve Development at Gaged Streams Based on discharge measurements made in WY , data were sufficient to develop stagedischarge rating curves at gages on two creeks, Horse Creek and Freeman Creek. The Lower Horse Creek gage, located on the alluvial fan below the Horse Creek at Mountain Front gage, is in an ephemeral stream reach where flow was routinely observed and measured, and a rating curve developed. Continuous stage measurements from cap rod gages at the mountain fronts of Freeman and Horse creeks were converted to discharge based on empirical rating curves (Figures 5-7), as summarized in Table 3. Curves and data used to develop the curves are included in Appendix B spreadsheets. For the Upper Horse Creek Gage, measurements of stage obtained in the winter and spring of WY2009 result in more measured velocity and computed flow than stage measurements obtained in fall 2009 through WY2011. The likely cause of this condition is deposition of material in the channel from a June 2009 run-off event. The change in the stage-discharge relationship can be seen in Figure 7, and is partitioned into rating curves presented in Figures 8 and y = x x R² = Stage, in feet Freeman Creek Figure 5: Stage-discharge relationship for Freeman Creek (gage site #110). INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 12

18 Flow, in cfs Flow, in cfs y = x R² = Stage, in feet Lower Horse Creek Figure 6: Stage-discharge relationship for Lower Horse Creek (gage site #107) Stage, in feet Spring 2009 Fall Figure 7: Stage-discharge relationship for Horse Creek at Mountain Front (gage site #106), showing curve shift. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 13

19 Flow, in cfs Flow, in cfs y = x x R² = Stage, in feet Spring 2009 Figure 8: Stage-discharge relationship for Horse Creek at Mountain Front and WY2009 rating curve y = x x R² = Stage, in feet Fall Figure 9: Stage-discharge relationship for Horse Creek at Mountain Front and WY rating curve. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 14

20 Table 3: Rating curves for mountain block streams. Site Rating Curve R 2 n Freeman Creek y = X Lower Horse Creek y = x Horse Creek at Mtn Front (WY2009) Horse Creek at Mtn Front (WY ) y = x x y = x Based on the rating curves, total observed flow for each water year was computed for Freeman, and Horse Creek s two stations and is presented with precipitation values from the U.S. Navy Centroid station by water year in Figure 10. WY2009 was a partial water year for the period of record of all capacitance rod gage stations in the study area with no data recorded from October, 2008 through early March, Precipitation at the Centroid facility was recorded as 4.33 inches in WY2009, 2.86 inches in WY2010 and 5.2 inches in WY2011. The near doubling of precipitation between WY2010 and WY2011 is likely the reason for the large increase in flow from WY2010 to WY2011 as seen in Figure 10. Centroid Precipitation (in) Lower Horse Creek (AF) * 728 WY2011 Upper Horse Creek (AF) 291* WY2010 WY2009 Freeman Creek (AF) 80 77* Figure 10: Precipitation and flow by water year. *WY2009 was a partial water year for monitoring. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 15

21 Section 3 - Estimating Discharge at the Cap Rod Stations Discharge Estimates Based on Stage Data from Cap Rods At each cap rod site, stage - discharge relationships were established by solving Manning s equation for discharge (Dunne and Leopold, 1978), Q = AR n S Eq. 1 where Q is discharge in cubic feet per second, A is the cross-sectional are of flow in the channel (ft 2 ), R is the hydraulic radius (ft) defined as A/P, where P is the wetted perimeter (ft) of the channel, S is the channel slope (ft ft -1 ), and n is Manning s roughness coefficient. Transect data from channel surveys provided data on channel cross sections and slope. Manning s n estimates where made from field observations using information from French (1985), ranging from 0.2 to 0.5. In order to determine hydraulic parameters of A and R at various stages, multiple simulations were run using HEC-RAS (US Army Corp of Engineers, 2010). Channel cross section data from field surveys (Appendix A) were used for geometric parameterization and theoretical stage data were used for calculating variables A and R, using a hypothetical Qi. Qi is only used to generate the channel geometry parameters based on variable stages that the hypothetical flow produces in the surveyed channel cross section. Models were run at steady state with upstream and downstream boundary conditions set at a normal depth (channel slope). Hydraulic variables A and R from HEC-RAS simulation outputs were then used to solve Manning s equation for Qm, the actual calculated flow, from which rating curves for computed stream channel discharge were generated to correlate to measured stage for each gage site. During the course of field activities in WY2010, several run-off events were observed from which instantaneous field measurements of flow were obtained along with corresponding gage height. These field measurements were used to refine the Manning coefficient (n) for site conditions and the Manning equation based stage-discharge rating curves (Interflow Hydrology, 2011). Manning's n coefficient was generally increased at gage sites by 0.05 to 0.1 above the initial estimated values. Additionally, for a few gage sites, notably at Spring Creek (Site #20), refinements in the channel slope (S) value were also made to be more strongly dependant on the up-stream gradient. The refinements to the Manning's equation variables improved the match between the field measured discharge and the computed discharge using the stage-discharge relationships. A comparison of the gaged versus computed discharges is presented in Table 4. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 16

22 Table 4: Comparison of Theoretical Discharge versus Measured Discharge for Measured Discharged Events Gage Site No. Gage Site Description Event Date Event Time Measured Flow (cfs) Manning Equation based Rating Curve Flow (cfs) 107 Lower Horse Creek (ephemeral) 10/4/ : Dixie Valley Wash at Box Culvert 10/5/ : Dixie Valley Wash at Box Culvert 10/7/ : Channel at Eastside of Playa 10/5/ : Spring Creek above Playa 10/5/ : Spring Creek above Playa 10/7/ : Channel Eastside Playa Culvert 10/5/ : Estimates of Annual Discharge at Cap Rod Gage Sites Water-Year 2009 Annual volumes of stream discharge are summarized for the period of record in WY2009 in Table 5. Hydrographs of recorded stage and computed discharge over time are presented in Appendix C. Gage sites up gradient from playa were recorded considerably more discharge by volume as contrasted with gages near the playa. The highest computed flow rates occurred at the Dixie Wash at Sand Dune Pass (#109) gage with estimated peak flow of approximately 1,200 cfs during a significant precipitation event on June 1, 2009, as recorded at the US Naval Centroid weather station. Another significant run-off event occurred on August 23, 2009 which damaged the gage at site #109 and prevented accurate stage measurement during the event. Field reconnaissance and surveying of the high water marks after the run-off event suggest that the peak flow was approximately 1,500 cfs. In order to estimate the WY2009 total discharge from gaged channels, the flow data were "upscaled" based on their period of record and the average monthly precipitation observed at the U.S. Navy Centroid weather station (Table 6). For instance, Cap Rod #91 was successfully monitored without interruption from March through the end of the water year. In that seven month period, 50.1% of the total water year precipitation was recorded at the Centroid station. To account for discharge during the 5 months prior to gage installation, the total observed flow is basically doubled (50% added) to provide an estimate of potential discharge for the complete water year (Table 5). The scaling method is simplistic, but provides a ball-park estimate of total annual discharge for WY2009. However, sites that experienced what appear to be isolated extreme events, such as Dixie Valley Wash (#109), were not up-scaled in this manner. The assumption applied is that large events are infrequent in the record. The scaling process was not applied to the perennial/intermittent stream gages at the mountain fronts and on the alluvial fans. No estimates of total discharge were made for these sites for WY2009. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 17

23 Table 5: Summary of capacitance rod for WY2009 with observed and up-scaled (total WY) flow estimates. Cap Rod Site ID Number Name Date Deployed Days on Record, 2009 Months Successfully Monitored Percent of Annual Precipitation for Monitored Months Gaged Flow (AFA) Up-scaled (Est.) Annual Flow (AFA) 11 Unnamed playa culvert 3/4/ March-September 50.1% Spring playa 3/4/ March-September 50.1% Shoshone playa 3/5/ March-September 50.1% Bernice playa 3/5/ March-September 50.1% Unnamed playa channel 3/5/ March-September 50.1% Deer Lodge playa 3/5/ March-September 50.1% Unnamed playa channel 3/5/ March-June 42.0% Unnamed playa channel 3/5/ March-September 50.0% Unnamed playa channel 3/5/ March-June, September 44.0% Dixie Valley playa - primary channel 8/26/ September 2.1% Dixie Valley playa - secondary channel 6/25/ June - August NA Unnamed playa culvert 3/4/ March-September 50.1% Unnamed playa culvert 3/4/ March-September 50.1% Unnamed playa culvert 3/4/ March-September 50.1% Horse Mountain Front 3/25/ April - September Lower Horse Creek 3/25/ April - September Dixie V. Sand Dune Pass 3/25/ April - September 39.0% * 110 Freeman Mountain Front 3/25/ April - September Cottonwood Mountain front 3/26/ April-June (gage lost in flood) Lower Cottonwood Cr. 3/26/ April-May, July-September 33.1% Shoshone Cr. Below Shoshone Meadows 3/26/ March-June, September 44.0% Spring Pleasant V. Sub-Basin Bdy. 3/26/ April - June 25.0% Cow/Deep Mtn. Front 3/31/ May-September 36.0% Dixie Valley Box Clvt. On SR 121 4/6/ May-September 41.9% * no up-scaling applied INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 18

24 Table 6: Monthly average precipitation at the U.S. Navy Centroid Station, Month Average Precipitation (in) Percentage of Annual Precipitation January % February % March % April % May % June % July % August % September % October % November % December % Total % Water-Year 2010 and 2011 Computed volumes of flow for water years 2010 and 2011 are presented in Table 7, and are contrasted to WY2009 estimated flows. No run-off events were recorded at the Dixie Valley at Sand Pass (#109) gage in either WY2010 or WY2011. Other variability in recorded run-off during the period of record are described in forthcoming Section 4 of this report. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 19

25 Table 7: Summary of discharge measurements for gages in Dixie Valley, WY WY2011. Cap Rod Site ID Number Name WY2009 Observed Flow (AFA) WY2009 Up-scaled Flow (AFA) WY2010 Observed Flow (AFA) WY2011 Observed Flow (AFA) 11 Unnamed playa culvert Spring playa Shoshone playa Bernice playa Unnamed playa channel Deer Lodge playa Unnamed playa channel Unnamed playa channel Unnamed playa channel Dixie Valley playa - primary channel Dixie Valley playa - secondary channel Unnamed playa culvert Unnamed playa culvert Unnamed playa culvert Horse Mountain Front Lower Horse Creek Dixie V. Sand Dune Pass * 0 Unknown** 110 Freeman Mountain Front Cottonwood mountain front Lower Cottonwood Cr Shoshone Cr. Below Shoshone Meadows Spring Pleasant V. Sub-Basin Bdy Cow/Deep Mtn. Front Dixie Valley Box Clvt. On SR * no up-scaling applied, **=Cap Rod 109 was malfunctioning in WY2011 INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 20

26 Section 4 Discussion and Observations Contrasts in Water-Year Flows Review of Table 7 provides insight into the spatial and temporal variability of stream discharge and ephemeral channel run-off in Dixie Valley. For WY2009, the highest flows in ephemeral channels leading to the playa were observed at Dixie Wash (#125) and Spring Creek (#20). Also evident in the WY2009 data is a majority of the flow in Dixie Wash infiltrated before actually making it to the playa, as observed in the difference between computed (estimated) flows in Dixie Wash at gage sites #109 and #125. The marked reduction in computed discharge along Dixie Wash is interpreted to be due to stream bed infiltration. Significant run-off events in Dixie Wash were not recorded in water years 2010 or Mountain front gage sites recorded significant discharges of water, but consistently over the period of record, it did not appear that these flows reach the playa as run-on. In WY2010 a significant relative increase in flow was observed at gages #73 and #77 on the east side of the playa, and at the culvert site 93. By contrast, no significant discharge was recorded in Dixie Wash. Spatial variability throughout Water Years 2009 and 2011 are contrasted in Figure 11. In WY2011 many sites experienced increased flow as contrasted with WY2010; however Spring Creek (#20) was dominantly responsible for delivering water to the playa. In spite of this increase in recorded flow from WY2010 to WY2011, very little flow was observed for watersheds west of the playa. The total recorded playa run-on in WY2009 for the partial year record is approximately 160 acrefeet, as recorded at gage sites surrounding the playa (Table 8). The up-scaled estimate of total WY2009 discharge at gages near the playa periphery is 370 acre-feet. This contrasts with computed discharges of 250 acre-feet and 380 acre-feet for water years 2010 and 2011, respectively. In summary, total gaged and estimated run-on to the playa ranges from 250 to 380 acre-feet, and over the three period of record, averaged about 330 acre-feet per year. The spatial distribution of playa run-on is notably variable. WY2009 was dominated by run-on from the major northern and southern tributaries, Spring Creek and Dixie Wash. WY2010 was dominated by run-on from the northern and eastern watersheds, with very little run-on from Dixie Wash. WY2011 was dominated by northern discharge to the playa from Spring Creek. In all three years, very little runon to the playa was recorded from the western watersheds. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 21

27 Table 8: Computed Discharge onto the Dixie Valley playa, WY2009 WY2011. Playa Cap Rod Site ID Number Name Observed Flow WY2009 Upscaled Flow, WY2009 Observed Flow WY2010 Observed Flow WY2011 (AFA) (AFA) (AFA) (AFA) 11 Unnamed playa culvert Spring playa Shoshone playa Bernice playa Unnamed playa channel Deer Lodge playa Unnamed playa channel Unnamed playa channel Unnamed playa channel Dixie Valley playa - primary channel NQ NQ 87 Dixie Valley playa - secondary channel Unnamed playa culvert Unnamed playa culvert Unnamed playa culvert Dixie Valley Box Clvt. On SR Total (values rounded): NQ= Not quantified, no rating curve for this site because it was observed to not capture all flow from up-stream areas. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 22

28 Figure 11: Spatial variability of observed flow to the Dixie Valley playa. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 23

29 4.3 - Estimating Total Playa Run-On In order to estimate total playa run-on from gaged and ungaged watersheds, empirical estimation techniques were attempted that incorporated both the active channel width of ungaged streams and an analysis using watershed areas. Equations for stream discharge based on the active channel width (ACW) developed by Hedman and Osterkamp (1982) were compared with computed discharge of gaged streams. Ultimately, the variability observed in both the distribution and magnitudes of discharge limited the ability to define strong relationships with the ACW parameter. Using the gaged watersheds in Dixie Valley, watershed area-based regression methods were examined, but determined to be heavily reliant on Spring Creek and Dixie Wash data to define the regression curve. Without Spring Creek and Dixie Wash anchoring the trend, little correlation exists. This fact is mainly due to: The spatial variability of discharge measured during the monitoring effort (see Figure 11). Many precipitation events in Dixie Valley do not uniformly distribute precipitation over the entire valley and are sometime isolated bursts that do not contribute flow to all watersheds. Watershed area/discharge relationships that can be typical in many regions may be complicated in Dixie Valley due to significant losses along stream channels and large alluvial fans, and the geomorphic differences between major valley floor drainages, alluvial fan drainages from the Clan Alpine Range, and alluvial fan differences from the Stillwater Range. However, more geographically refined watershed area-discharge relationships may be defined, for example, for the set of watersheds draining to the playa from the alluvial fans of the Clan Alpine Range (See Figure 12). A similar relationship for the west-side watersheds from the Stillwater Range is likely, but only 4 gage site cover the geographic area (Figure 12). In estimating the annual run-on value to the playa, inclusive of potential run-on from ungaged watersheds, the following factors were considered: On an annual basis, the largest contributors to playa run-on are Spring Creek (#20), Dixie Valley Wash (#125), and Shoshone Creek (#31) (see Table 8). On the west side of the playa there are approximately 77,065 acres of contributing area, with 48,874 acres, or roughly 63% being ungaged (Figure 12). In general, the ungaged watersheds are similar in size and altitude to gaged west-side watersheds. The average total INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 24

30 flow from all gaged watershed on the west side of the playa was 22 AF/yr. Up-scaling this value to account for an equal volume of discharge from the ungaged watershed area equals 58AF/yr for the west side of the playa. Along the east side of the playa, total watershed area is 220,783 acres with 104,828 acres of gaged watershed (Figure 12). Watershed areas marked as A through F are ungaged areas with a total area of 115,955 acres, or 52%. The average flow from gages on the east side of the playa was 103 AF/yr. Up-scaling based on watershed area produces a total average run-on estimate of 214 AF/yr. Alternatively, the east-side watersheds show an apparent relationship with average annual discharge and watershed area as shown in Figure 13. Using this relationship applied to the ungaged areas yields 327AF/yr of total average run-on from east-side ungaged and gaged watersheds. Watershed area G is gaged by capacitance rod 86, however it was discovered that the channel does not capture all of the flow in the area, therefore a quantification is not possible for the Dixie Wash watershed, nor is it possible to determine the infiltration of flow between capacitance rod 125 and 86. Instead, the total average value of flow from gage site #125 is used for watershed area G, and up-gradient portions of Dixie Wash. Between WY2009 and WY2012, the average flow for gage site #125 is 39AF/yr. Therefore, the estimate for average annual run-on to the playa, adjusted to include ungaged watersheds, can be estimated as follows: Average Flow for Spring Creek (122 AF) + Average Flow for Dixie Wash at S.R. 125 (39AF) + Up-scaled West-Side Watersheds (58AF) + Up-scaled East-Side Watersheds (214 to 327AF), resulting in an estimated average playa run-on of 432 to 546 AF/yr. A reasonable estimate for annual run-on is rounded to approximately 500 AF/yr. In any given year, however, the total runon to the playa could vary considerably based on weather and climate conditions. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 25

31 Figure 12: Gaged and ungaged watershed areas tributary to the Dixie Valley playa. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 26

32 Average Discharge WY2009-WY2012, AF y = 0.003x R² = Watershed Area, Acres Figure 13: Regression of watershed area and measured annual flow between WY2009 WY2012 for eastern Dixie Valley playa gage sites 31, 40 56, 68, 73, 77, and Precipitation and run-off events During the Water Years 2009 and 2011 most runon occurred from October through June. With few exceptions, August and September produced nearly no noticable flow in the gaged ephemeral channels near the playa. An exception was the summer run-off events in 2009, which produced notable flows in Dixie Wash, and at some other gage locations. The precipitation event on the June 1, 2009 produced a flash flood in Cottonwood Canyon (site #112) which washed away the gage, scoured and redeposited tons of sediment from the channel, and damaged the downstream gage at Lower Cottonwood (site #113). Cottonwood canyon has a large drainage area of 21.9 mi 2 and a history of flash flood events (Benoit, personal communication). Post-event cross section resurvey (Figure 13) found considerable scouring that lowered the channel bed by 2 to 5 feet and more than doubled the width of the channel. It is noteworthy that this significant event was not registered at the downstream Spring Creek gage (site #20), yet it did register and damage the gage at site #113 (Lower Cottonwood). It appears this large flow event was retained and infiltrated in a subsidence feature located north of the Dixie Geothermal Power Plant, locally called "Lake Dixie". This topographic depression of land surface has been caused by the pumping at the geothermal plant. Significant subsidence cracks may have accommodated infiltration of water retained in Lake Dixie. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 27

33 6/25 C.L. CREEK CAP ROD RIGHT BANK Elevation (ft) LEFT BANK 6/25 HIGH WATER channel bed before large precip. event channel bed after large precip. event Distance (ft) Figure 13: Site #112 Cottonwood Creek comparison of 2009 pre & post flash flood cross-sections Photographs 6 and 7 demonstrate the magnitude of sediment scoured from the channel. Photograph 6 was taken about a ¼ mile upstream of site #112 and prior bed elevation is indicated by bed material on granite face approximately six feet above the post flood bed elevation. Photograph 7 shows the debris on the alluvial fan between sites #112 and #113. Due to high sediment load, active channel realignment and generally poor site conditions, site #112 was not reestablished. Photo 6: Cottonwood Creek post flood - 6/9/09 Photo 7 Cottonwood Crk btwn Sites 112 & 113-6/24/09 INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 28

34 A significant run-off event was documented in Dixie Valley between October 4 and 6, 2010 (Photos 8 and 9). Major ephemeral washes surrounding the playa were noted to be near bank-full conditions, with some locations, such as Spring Creek, flowing above its banks in an apparent flood stage. At the Spring Creek gage (#20), flow was measured with using a velocity meter at 4.2 cfs with water depths of 1.9 feet in the main channel. Field measurements during these flow events facilitated subsequent refinements and calibration of the synthetic rating curves derived using Manning's equation (Section 3.1). Photo 8: Gage Site #77 along east side of playa - 10/6/2010 Photo 9: Start of Run-off Event in Spring Creek, near Gage Site #20-10/4/10 During the project period, annual precipitation was recorded at the U.S. Navy Centroid Station, and at four weather stations operated by the USGS in central Dixie Valley. These stations are the Low Vegetation (LV) Station, the High Vegetation (HV) Station, Playa Station 1(P1), and Playa Station 2(P2). Locations of the weather stations are shown in Figure 3. Daily values for these stations are presented in Figures 14a through 14c. In addition, selected gage data from channels leading to the playa are presented in Figures 15a through 15c. Both the precipitation and flow data show significant variability, thus demonstrating spatial variance. Not all precipitation events cause a flow response in the channels, a factor that is complex and may rely on the timing and intensity of storm events, pre-existing soil moisture conditions and many other factors. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 29

35 Figure 14a: Precipitation at USGS weather stations and the U.S. Navy Centroid Facility, Dixie Valley Water Year 2009 USGS LV Site All USGS Sites Installed March, Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Precipitation (in) USGS HV Site USGS P1 Site USGS P2 Site 1.0 Month, Water Year U.S. Navy Centroid Station Oct/2008 Nov/2008 Dec/2008 Jan/2009 Feb/2009 Mar/2009 Apr/2009 May/2009 Jun/2009 Jul/2009 Aug/2009 Sep/2009 Oct/2009 Date INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 30

36 Figure 14b: Precipitation at USGS weather stations and the U.S. Navy Centroid Facility, Dixie Valley Water Year 2010 USGS LV Site 0.0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct USGS HV Site Precipitation (in) USGS P1 Site USGS P2 Site U.S. Navy Centroid Station Month, Water Year Oct/2009 Nov/2009 Dec/2009 Jan/2010 Feb/2010 Mar/2010 Apr/2010 May/2010 Jun/2010 Jul/2010 Aug/2010 Sep/2010 Oct/2010 Date INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 31

37 Figure 14c: 14b: Precipitation at USGS at USGS weather stations and and the the U.S. U.S. Navy Navy Centroid Facility, Dixie Dixie Valley Valley Water Year 2011 USGS LV Site 0.0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Precipitation (in) USGS HV Site USGS P1 Site USGS P2 Site U.S. Navy Centroid Station Month, Water Year Oct/2010 Nov/2010 Dec/2010 Jan/2011 Feb/2011 Mar/2011 Apr/2011 May/2011 Jun/2011 Jul/2011 Aug/2011 Sep/2011 Oct/2011 Date INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 32

38 Figure 15a: Selected capacitance rod hydrographs and precipitation from the U.S. Navy Centroid Facility, Dixie Valley Water Year 2009 Flow (cfs) Flow (cfs) Flow (cfs) Flow (cfs) Spring Creek 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Dixie Wash (Cap Rod 125) Cap Rod 31 Cap Rod 83 Cap Rods Installed March, Precipitation (in) U.S. Navy Centroid Station Oct/2008 Nov/2008 Dec/2008 Jan/2009 Feb/2009 Mar/2009 Apr/2009 May/2009 Jun/2009 Jul/2009 Aug/2009 Sep/2009 Oct/2009 INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 33 Date

39 Figure 15b: Selected capacitance rod hydrographs and precipitation from the U.S. Navy Centroid Facility, Dixie Valley Water Year 2010 Flow (cfs) Spring Creek (Cap Rod 20) 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Flow (cfs) Dixie Wash (Cap Rod 125) Flow (cfs) Flow (cfs) Cap Rod 31 Cap Rod 83 Precipitation (in) U.S. Navy Centroid Station Oct/2009 Nov/2009 Dec/2009 Jan/2010 Feb/2010 Mar/2010 Apr/2010 May/2010 Jun/2010 Jul/2010 Aug/2010 Sep/2010 Oct/2010 Date INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 34

40 Figure 15c: Selected capacitance rod hydrographs and precipitation from the U.S. Navy Centroid Facility, Dixie Valley Water Year 2011 Flow (cfs) Spring Creek (Cap Rod 20) 0 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Flow (cfs) Flow (cfs) Flow (cfs) Cap Rod 125 Cap Rod 31 Cap Rod 83 Precipitation (in) U.S. Navy Centroid Station Oct/2010 Nov/2010 Dec/2010 Jan/2011 Feb/2011 Mar/2011 Apr/2011 May/2011 Jun/2011 Jul/2011 Aug/2011 Sep/2011 Oct/2011 INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 35 Date

41 5/29/09 5/30/09 5/31/09 6/1/09 6/2/09 6/3/09 6/4/09 6/5/09 Discharge (cfs) Stream Channel Recharge Observations and measurements of perennial, intermittent, and ephemeral stream flows at the mountain front sites indicate, with the exception of large rain precipitation events, nearly all the flow past the mountain front is infiltrated on the alluvial fans before reaching the valley floor. Additionally, significant infiltration occurs along valley floor channels before reaching the playa, particularly along Dixie Wash. A significant event occurred on June 1, 2009 at the Dixie Wash at Sand Dune Pass (#109) which damaged the capacitance rod. However, subsequent channel crosssection resurvey and determination of the high water mark indicate a peak flow of approximately 1,200 cfs. This is contrasted with only 100 cfs observed at the Dixie Wash at Box Culvert (#125) site (Figure 16), demonstrating the significant infiltration losses along the approximate 25 mile length of wash between the gages (Figure 17). It is likely that most of this infiltration resulted in groundwater recharge, although a portion was also likely to have been retained in near-surface soils and subsequently lost to evaporation or transpired by plants Dixie Wash at Sand Dune Pass Dixie Wash at Box Culvert Figure 16: Graph of estimated peak flow recorded in Dixie Valley Wash at two stations. The gages are approximately 25 miles apart, and the peak flow was detected at the box culvert roughly 24 hours after it passed the Dixie Wash at Sand Dune Pass station. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 36

42 Figure 17: Southern Dixie Valley and Dixie Wash gage stations. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 37

43 Fault structures may also play a direct or indirect role in facilitating groundwater recharge from stream flows, particularly the Dixie Valley fault system which extends throughout most of the length of Dixie Valley along the mountain front on the east side of the Stillwater Range (Photos 10 and 11). An aerial tour of the valley on April 21, 2009 revealed flow in most channels up-gradient of the mountain front/alluvial fan interface which also coincides with many of the faults, including the Dixie Valley fault. Flows diminished rapidly across the fault and alluvial fans well before reaching the valley floor. Numerous reconnaissance investigations during fieldwork and stream flow measurements have supported this general observation. The Freeman Creek gage (site #110) is located immediately up-gradient from the Dixie Valley fault and flows into a stock pond directly over the fault scarp. Flows up to approximately 1cfs infiltrate rapidly near this scarp and on the upper most alluvial fan before the pond overflows and water is subsequently infiltrated on the upper and middle segments on the alluvial fan, well before reaching SR 121 or Dixie Wash. Photo 10: Stillwater Drainages & DV Fault 4/21/09 Photo 11: Dixie Valley Fault viewed North 4/21/09 Horse Creek drains a portion of the Clan Alpine Range in eastern Dixie Valley with gaging stations (#106 and #107) located approximately 2.3 miles apart (Figure 18). Flow observed at the Horse Creek gages is shown by water year in Figures 19 through 21. The highest annual discharge for Horse Creek occurred in WY2011 at 1,244 AF, however, the highest instantaneous measurement recorded at the gage occurred on June 9, During this event, a flow of nearly 5 cfs is computed, and is suspected to be one potential cause for the shift in the rating curve for the Horse Creek at the Mtn Front gage (Section 2.2). Partial water year 2009 was observed to have 141 AF of loss in stream discharge between the upper and lower Horse Creek gages. In WY2010 approximately 433 AF of stream flow was lost, and in WY2011, approximately 516 AF was lost. Assuming a majority of the stream flow loss is resultant of infiltration which produced recharge to the groundwater system, these losses indicate an annual recharge rate along the alluvial fan portion of Horse Creek of approximately 200 AF/yr per mile of stream channel. Below the Lower Horse Creek gage (#106), most all stream flow eventually lost to infiltration and evapotranspiration processes on the lower alluvial fan complex. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 38

44 Figure 18: Gaging station locations along Horse Creek and the Horse Creek alluvial fan, Dixie Valley. INTERFLOW HYDROLOGY AND MAHANNAH & ASSOCIATES Page 39