APPENDIX E Geomorphic Channel Surveys. October 2004

Transcription

1 APPENDIX E October 2004 Tessera Consulting Gretchen E. Hayes In association with Sonoma Ecology Center Elisabeth Micheli Cynthia Rossi Rebecca Lawton

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3 Contents Objective... E-1 Methods... E-1 Preparation... E-2 Base Maps... E-1 Longitudinal Profiles... E-2 Access Agreements... E-2 Supplementary Information and Maps... E-2 Fieldwork... E-3 Data Management... E-4 Data Analysis... E-5 Results: Preliminary Observations of Geomorphic Processes on Sonoma Creek Tributaries... E-5 Asbury Creek: Summary... E-6 Calabazas Creek: Summary... E-7 Fish Barriers... E-8 In-stream Structures... E-8 Large Woody Debris Impediments to Migration... E-8 Riparian Cover... E-8 Water Supply... E-8 Sedimentation... E-9 Correlation of Stream Morphology with Watershed-scale Landforms... E-9 Asbury Creek... E-10 Calabazas Creek... E-10 Recommendations for Further Study... E-10 Water Budgets... E-11 Groundwater Dynamics... E-11 Stream Flow Measurements... E-11 Watershed-scale Landform Influences... E-11 Subwatershed Lanform Mapping... E-11 Landslide Map Analysis... E-12 Complementary Fieldwork... E-12 References...E-17 Tables Table E-1. Summary of Geomorphic Attributes of Two Representative Tributaries.... E-13 i

4 Table of Contents Figures Figure E-1. Asbury Creek, River Stations E-14 Figure E-2. Calabazas Creek, River Stations E-15 Figure E-3. Calabazas Creek, River Stations E-16 ii

5 OBJECTIVE This report provides a preliminary summary of geomorphic field surveys conducted in October to November 2003 on Asbury and Calabazas Creeks, two tributaries to Sonoma Creek. This data is important for understanding physical processes controlling the ecological value of aquatic and riparian habitat in tributary streams to Sonoma Creek. The research objective of this study is to identify geomorphic processes influencing fish habitat in hillside tributaries to Sonoma Creek. In lieu of surveying all the tributaries to Sonoma Valley, two hillside streams were selected for a comparative study: Asbury Creek to the west, and Calabazas Creek to the east. Asbury and Calabazas Creeks were selected for study because they differ greatly in fish habitat quality, and because they represent a broad range of geomorphic conditions that occur on the majority of other tributaries to Sonoma Creek. According to previous fish habitat studies conducted by the Sonoma Ecology Center (SEC), Asbury Creek has reduced quality fish habitat and is representative of west-side tributaries to Sonoma Creek. The west-side creeks draining Sonoma Mountain are characterized by relatively small drainage areas, steep slopes, and high fine sediment loads. The high loads of fine sediment may be due in part to historically intensive land and water-uses (including clearcut logging and water diversions). By contrast, Calabazas Creek has relatively high fish habitat quality, and is geomorphically representative of east-side Sonoma Valley tributary streams draining the Mayacamas Range. The technical objective of this study is to establish a repeatable protocol for collecting and mapping geomorphic field data in the Sonoma Valley Watershed. Emphasis was placed on exploring ways to maximize the efficiency of field data collection and transfer to electronic format, such as for use in Geographic Information System (GIS) mapping and analysis. To this end, a combination of manual and electronic data collection methods was employed in the field. The field methods are presented in detail below so that researchers may replicate this protocol in other Sonoma Valley tributary watersheds as resources become available. METHODS In order to identify geomorphic processing influencing aquatic habitat, we characterize the geomorphic processes acting on the stream channel over varying spatial and temporal scales. At the stream reach scale, our approach is to characterize stream reaches by stream morphology, dominant channel substrate, sediment storage types and volumes, streamflow, and primary geomorphic transport processes acting on the channel. At the watershed scale, we identify large-scale erosional and depositional landforms intersecting the creek network to infer dominant geomorphic process and identify major sediment sources (See Map Plate 4: Landform Units, Sonoma Creek Watershed Limiting Factors Analysis, 2006). Sources of sediment to the channel include hillslopes, floodplains, channel banks, and channel bed material storage areas such as point bars. Sediment is transported from these areas by mass wasting (colluvial) and channel flow (fluvial) processes, including: soil creep, earthflows, landslides, slope failure, tree throw, bioturbation, hillslope incision (gullying), streambank erosion, fluvial transport of channel bedload, and stream channel incision. These data can be used to estimate the scale and periodicity of sediment transport to the stream channel. This geomorphic data can also be used to frame hypotheses about how local geology, landforms, and hydrology correlate with stream attributes as a basis for predicting the location and quality of stream habitat. E-1

6 Preparation Base Maps An accurate base map is the key reference for all data collected in the field. This study was conducted in conjunction with other research projects pertaining to the Sonoma Creek Watershed Limiting Factors Analysis, and utilizes the spatial data collected as part of those studies. Both a hardcopy and a digital map are essential for ease of data collection and storage. We start by using the GIS database to digitally producing a field map that consists of an aerial photo scale 1:6,000, with white 40 foot elevation contours, blue streams, red roads, blue watershed boundary, relevant landmark data, a legend, a scale bar, a North arrow, creation date, and reference data. To establish a spatial referencing system that can be duplicated in the field with a measuring tape, we segment the target tributary creek into routed stations, starting with 0 at the confluence of Sonoma Creek, and tick-mark every 100 feet, but label only every 1000 ft. For brevity, we label station 1000 as station 1 and indicate in the legend that the stationing is multiplied by 1000 ft. (i.e. a 10,000 ft stream would have labels 1-10 with 100 ticks). So that the site can be easily re-located, we map parking spots, and note locations and relevant information for access and egress. Longitudinal Profiles Using the GIS, we obtain and tabulate the elevation for each routed stream station so that the stream profile can be plotted in a spreadsheet program. The stationing along the tributary is also used to graph geomorphic attribute data on the longitudinal profile of the creek. Access Agreements Necessary landowner permissions are obtained previous to embarking on fieldwork. We bring signed forms, which contain landowner names and contact information, into the field along with a map showing landowner boundaries. Supplementary Information and Maps To assist with inferring potential correlations between geomorphic attributes and other geographic factors, we compile and bring into the field other reference maps such as historic and current USGS topographic quadrangles; land use maps; curvature maps; detailed trail, property, and road guides; hardrock and Quaternary geology; faults; soils; watertable and hydrology; and landform maps. Other maps may be created to assist in the identification of geomorphic processes in the study area, including: A gross scale landform map, including boundaries of historic water bodies (some landforms may be from relic geomorphic processes, i.e. processes which are no longer active today) (See Map Plate 4: Landform Units, Sonoma Creek Watershed Limiting Factors Analysis, 2006) A slope curvature map to define erosional and depositional zones A combination map for predicting areas of potential erosional processes (i.e. debris flow zones based on stream density, slope, substrate, curvature) E-2

7 Fieldwork In the field, we walk the length of the entire stream channel and note changes in geomorphic attributes, described below, spatially referencing attributes by river station. Some data, such as dominant channel substrate, was mapped continuously along the length of the channel, while other data was mapped on a site specific basis. Another approach would be to characterize geomorphic attributes, such as valley slope and dominant channel substrate, by channel reach. Whether continuously, by reach, or on a site specific basis, geomorphic attributes must be recorded by river station so that the data can be replicated in a GIS or spreadsheet. We located stations in the field simultaneously with a Geographic Positioning System (GPS) instrument, field map analysis, and/or extending a survey tape from an identifiable location along the stream thalweg as appropriate. Often a combination of electronic GPS unit and field mapping methods are required to make sure river stations are accurately referenced, especially in deep canyons, or during temporal windows when the GPS unit cannot communicate with satellites. For more complete data collection, we use redundant and complementary methods to record field data. Logistically, to collect data efficiently, a minimum of two people, and preferably three, are required to record data simultaneously with the GPS, fieldbook, and on a fieldmap. GPS entry is regimented and comparatively slower than notating field books, datasheets, and maps, however, the GPS data does not require re-entry back at the office. With two researchers recording data electronically and manually, a third person has the mobility to string the measuring tape and call out geomorphic attribute parameters to be recorded more efficiently. We create both a manual and an electronic GPS data input table to record multiple predetermined attributes along the length of the stream channel by river station. In both formats, we reference geomorphic attributes by stream station location. River stations are noted to the tenths place (i.e. STA 11.2 is 11,200 feet upstream from the confluence of Sonoma Creek). Before commencing fieldwork, we pre-program the GPS data input table with a stream attribute key by creating abbreviations for dominant channel bed substrate; dominant channel bank substrate and indications for which channel bank; wet/dry channel bed; and landslides. We leave note space to indicate other geomorphic attributes by river station. We also draw and labeled geomorphic attributes on the field map. To take full advantage of our time in the field, it is our objective to: Note changes in dominant channel substrate, with special notice of substrate stored in channel bars and pools of value for spawning and rearing habitat. Take rough measurements of point bar gravel storage areas. Indicate secondary substrate in areas where the bedload is clearly bimodal and indicate degree of embeddedness. Map areas of wet and dry channel. Map inflows from stream tributaries, springs and pipes, and measure dimensions. Identify point attributes influencing fish habitat including sediment sources, water supply features (natural and man-made), and fish barriers. E-3

8 Characterize stream geometry by reach. Classify stream morphology using the Montgomery-Buffington (1993, 1997, 1998) classifications. Take rough measurements of bank full width, depth to floodplain terrace, and channel width in representative stream reaches with similar stream morphology and valley characteristics. Indicate bank composition. Indicate relative steepness of valley slopes. Note channel controls such as bedrock, hard structures, tree roots, faults. Map locations of large woody debris. Identify sources of sediment to the channel. Map location and measure dimensions of landslides, bank failures, and dry ravel to obtain an approximate volume of sediment input potential to the channel. Measure debris flow fans and slope failure volumes: toe height, distance along stream channel, and length upslope. Note the channel stations marking the beginning and end of large slope block failures along the stream. Indicate road and trail crossings and indicate dimensions and substrate. Map erosional and depositional landform units at a stream-reach/hillslope scale. Photograph points of interest. Note photo number and stream station in notebook and describe photo. Draw directional arrow on basemap and number with photo. In this study, we rely primarily on stream gradient estimates from the GIS DEM-generated longitudinal profile for additional analyses. In a handful of locations we measured a few manual approximate measurements in the steeper reaches of the stream channel using a hand-level to compare to DEM slope estimates. Data Management We synthesize the electronic and manual field data by mapping the above listed geomorphic attributes both in plan and cross section form. Field data is transferred to a GIS by digitizing field map notations and downloading data from the GPS instrument. The electronic GPS data on dominant substrate is easily mapped along the stream line generated by the DEM in the GIS. Maps produced by the Sonoma Ecology Center with the data from this study are not included in this report, but have either been incorporated in the Sonoma Creek Watershed Limiting Factors Analysis, or stored in the GIS database for later use. For the purposes of this report, we use a spreadsheet program to chart as many geomorphic attributes as possible in cross section, using the established river stations as points along the x- axis, and elevation as points along the y-axis (Figures E-1, E-2, E-3). Where possible, we obtain corresponding elevations for field attributes from the GIS, tabulate, and plot them on the longitudinal profile in a spreadsheet program. Routed stations are interpolated for the field data for which there is no GPS location data. We then plot the stream longitudinal profile with segments colored by dominant channel substrate. Create a key where substrate size declines with the progression of colors down the rainbow spectrum, such as follows: Red-boulder; Orange-cobble; Yellow-gravel; Green-sand; Violet-silt; Black-Bedrock in channel bottom. Grey lines indicate stream reaches with no data. Other attributes can be charted in cross section at relative locations along the stream channel using the river stations, but not necessarily using actual elevation. For example, on the E-4

9 enclosed Figures E-1, E-2, E-3, the location of incoming stream tributary confluences are plotted on the longitudinal stream profiles as vertical blue lines. The lines are not plotted to scale and therefore do not represent relative tributary length, but they do indicate the correct stream station of the tributary confluence. Plotting attributes schematically above the stream in cross section may be interpreted as being located on one side of the channel, whereas attributes plotted schematically below the stream in cross section may be interpreted at being located on the opposite stream bank. Map symbols are used to indicate where bedrock (Bedrock channel banks-various colors) and large woody debris (LWD-green lightning bolts) are located, but for graphic purposes, the symbols are not drawn to actual scale. Black lines indicate stream crossings or bridges on the enclosed maps. An old stream abutment is represented by a gray triangle. Data Analysis The final step is to analyze the maps and graphs to identify correlations between physical attributes and to infer causes and effects of geomorphic limiting factors affecting the stream channel and fish habitat. Further testing with GIS modeling, field checking, and monitoring are recommended. RESULTS: Preliminary Observations of Geomorphic Processes on Sonoma Creek Tributaries Following is a preliminary summary of some of the key geomorphic characteristics of Asbury and Calabazas Creeks collected during our October and November 2003 surveys (Table E-1). For the purposes of this preliminary report, this geomorphic attribute data has been graphed in cross sectional form only (Figures E-1, E-2, E-3). All collected geomorphic field attribute data has been added to the GIS spatial database at the Sonoma Ecology Center for future analysis and use in conjunction with related studies. Further analysis of the mapped field data is recommended to draw the most benefit from the surveys. Geomorphic differences may help to explain in part why Calabazas Creek has higher quality fish habitat compared to Asbury Creek. In general, Asbury Creek has more fish barriers, less stream discharge and power, a higher percent of water diversion, and higher percentages of fine sediment than Calabazas. Whereas Calabazas is relatively stable with a well-defined floodplain, Asbury Creek is unstable with several reaches experiencing bank erosion, bank slope failures, and channel incision. The bedload in both Asbury creeks is predominantly coarse, cobble sized or greater. Only 7% of the surveyed length of Calabazas Creek, and 9% of the surveyed length of Asbury Creek, have a primary bedload of gravel. On Asbury Creek, the mobile fraction of the bedload is stored in the channel, whereas on Calabazas the mobile bedload is stored in bars and on the floodplain as well as in the channel. The mobile supply of medium and small gravel (potentially suitable for spawning) is greater on Calabazas than on Asbury. While both streams display coarse substrate (cobble-boulder) reaches potentially suitable for rearing habitat, the cobbleboulder units on Asbury are more filled-in with fine sediments than the cobble bars on Calabazas Creek. In both systems, retention of coarse substrate (gravels to boulders) appears to be correlated with large woody debris deposits. E-5

10 Asbury Creek: Summary Asbury Creek is a spring-fed tributary to Sonoma Creek located on the western slope of the Sonoma Valley. Like most of the watersheds on the west side of the valley, the drainage area is relatively small, at approximately 1.1 square miles. The stream profile is concave progressing from very steep slopes near the watershed divide to moderate slopes near the confluence with Sonoma Creek. The upper (headwaters) reach is in a narrow V-shaped valley near the watershed divide. There is no floodplain or significant channel incision. The channel is boulder-dominated, and there are some bedrock exposures in the channel. The steep hillslopes are covered with a 4-5 feet deep mantle of dry ravel soil. The primary erosion processes are slope wash and tree fall. Extensive sections of stream in this reach are filled with large woody debris and trees that fell in from the steep side slopes. The next reach, located by the Upper Fallen Bridge Trail bridge crossing, is in the area corresponding to the scarp of the relic hillslope scale landslide in the adjacent orchard to the south. This channel reach is dominated by steep step pool morphology. Exposed channel banks reveal large boulders and cobbles in a sandy matrix. The channel goes dry in stretches. The dry reaches may be correlated with faults or changes in landforms, or may be due to a drawdown in the water table caused by water diversion from Asbury Creek or by well pumping. The middle reach of Asbury is unstable with numerous slope block failures on the right and left banks. The blocks extend feet upslope and feet along the channel. The slope block failures are composed largely of sandy soil. There is one debris flow tributary entering on the right bank, but vegetation cover indicates that this is relatively inactive. The channel in the middle reach is bimodal with a matrix of large cobble and boulders, and pools filled with fine sediments and organic debris. Small, poorly sorted gravel and cobble bars begin to appear in this reach. There are alternating sections of incised and not incised channel. Channel incision is high in places throughout this middle reach, up to 12 feet. The banks appear to be the dominant source of sediment to the stream channel. The stumps of logged redwoods on the terrace above the incised channel can be used to determine an approximate incision rate for the middle reach. There is a place in this reach where older redwoods anchor both the right and left banks of the channel, and there is no channel incision. This indicates that the deeply incised reaches upstream of this anchor point are not the result of upstream knickpoint migration. Numerous patches of large woody debris occur in this reach where the channel banks have failed and trees have fallen into the channel. Springs located halfway up some failed channel banks may indicate that the dropping of the water table may have contributed to treefall and bank incision in this reach. The middle reach of Asbury Creek is correlated with the adjacent hillslope landslide failure plane and debris deposit. Existing maps may not encompass the total extent and complexity of the relic slide. This reach, which contains the majority of bank failures, is correlated with the Medium Non-Conformal Relief unit on the Landform Map (See Map Plate 4: Landform Units, Sonoma Creek Watershed Limiting Factors Analysis, 2006). The lower reach of Asbury is located in the Sonoma Valley fan. The channel has a small floodplain in this reach and there is consistent discernable pool, riffle, glide morphology. There are areas with gravel bars, but fine sediments still dominate in the pools. The channel is incised approximately 5 feet throughout this reach. Where the channel can access its floodplain, there are limited areas of sandy overbank deposits of fines. The channel appears to be actively E-6

11 incising especially at meander bends. The banks appear to be the dominant source of sediment to the stream channel. The channel bed is beginning to incise into bedrock in this reach. The water-reworked, whitish colored tuff disintegrates into a fine powder. There is one major diversion structure that routes water from Asbury Creek to Fern Lake. The initial date of construction of the diversion, and the percentage of water diverted from Asbury Creek to Fern Lake is yet to be determined. There are no other significant drainage pipes into or out of the channel. Calabazas Creek: Summary Calabazas Creek is a spring-fed tributary to Sonoma Creek located on the eastern slope of the Sonoma Valley with a drainage area of approximately 12.6 sq. mi. Calabazas Creek has a moderate slope over the majority of the stream channel and is steep in relatively short sections most likely due to fault movement and bedrock control. By contrast, tributaries to Calabazas entering from the north and south are very steep. Calabazas is bedrock-dominated and controlled over the majority of the stream channel. Incision and bank erosion does not appear to be very active except for in the lower-most reach of the stream, in the Sonoma Creek Floodplain landform Unit (Map Plate 4). In the upper reach of the stream beginning at the confluence of the north and south forks, the stream is bedrock-controlled. Numerous springs enter near the fault zone in this oversteepened reach. The slope map generated from the DEM (See Map Plate 6: Stream Slope, Sonoma Creek Watershed Limiting Factors Analysis, 2006) underestimates the steepness of the stream slope in short sections of the channel in this reach. Debris flows from tributaries are the dominant erosion process and sediment source to the stream channel in this reach. Where the stream emerges from the canyon downstream to about Highway 12, the alluvial and soil cover over the bedrock is a maximum of 7 feet deep. This is the maximum incision depth in this bedrock controlled reach. Though slightly entrenched, this reach is dominated by discernable pool, riffle, glide morphology. The floodplain terrace is regularly accessed by the stream as evidenced by the fresh sandy overbank deposits. Fine sediments may not be prevalent in the stream channel because they are stored on the floodplain. Where the channel is wide enough, there are mid-channel cobble and boulder bars and secondary channels. The primary source of sediment in this reach is the gravel and cobble bars in the channel. Bank erosion appears to be a secondary sediment source. Land use in this reach is agricultural. There are a couple of drainage pipes to the creek floodplain from the adjacent road to the north. A few bridges and one old bridge abutment serve as other channel controls in this reach. The lower reach of Calabazas, downstream of Highway 12, in the valley fan is the most incised. Incision increases downstream, and is greatest within 3000 feet of the confluence with Sonoma Creek. In some places, incision has exposed four feet of bedrock in the channel. This lower reach also has the most suburban land development and corresponding impervious area. Creek setbacks are as little as five feet on some properties. Several pipes drain roads and personal properties directly into the creek in this reach. Although entrenched in the downstream most section, this reach is meandering and has large (120 feet long), well-sorted cobble bars. The primary source of sediment in this reach is the gravel and cobble bars in the channel. Bank erosion appears to be a secondary sediment source. E-7

12 Fish Barriers There are several characteristics of Asbury Creek that pose barriers to fish migration. These include in-channel structures and culverts; high steps relative to channel width and depth; large woody debris barriers; and extensive reaches of dry stream bed. In contrast, few potential or significant barriers to fish migration exist on Calabazas Creek until well upstream at the 14.5 foot high waterfall near the confluence of the north and south forks. In-stream structures There are two structures that may pose a barrier to fish migration on Asbury: the culvert at the confluence of the mainstem, and the spillway downstream of the diversion pipe to Fern Lake. Restoration efforts have been made to slow the velocity of the water passing through the culvert at the confluence to make it passable by fish. The installations have filled with sediment. The effectiveness of the installations for improving fish migration is undetermined. On Calabazas creek, there is a bridge abutment on the next road crossing downstream from Highway 12 that may pose a barrier to fish migration, although a fish ladder has been installed there. The Sonoma Ecology Center has surveyed this cross section and installed a staff plate on the bridge abutment. Large Woody Debris Impediments to Migration Although lack of large woody debris can be a limiting factor to the creation of suitable fish habitat, the preponderance of woody material in the channel in relation to channel depth and flow on Asbury creek appears to serve as a significant impediment to fish migration in several reaches. There were few log jams or debris piles on Calabazas and the few there were appear to be passable by fish. Riparian Cover Calabazas Creek appears to have denser riparian cover than Asbury Creek, particularly on lower elevation reaches. Water Supply Both Asbury and Calabazas Creeks are spring-fed. Calabazas has a greater contributing watershed area and a greater base flow than Asbury. Furthermore, there were no dry reaches on Calabazas up to the 14.5 foot high waterfall, where the survey concluded. In contrast, Asbury has extensive sections of dry channel bed. The dry reaches on Asbury may be associated with faults; changes in landform unit; changes in depth of alluvium; or with water diversion practices. Both Asbury and Calabazas have reaches of step-pool morphology. The steps on Asbury, however, are more likely to constitute fish barriers than those on Calabazas. The steps on Asbury tend to be denser per channel reach, and higher in proportion to the channel width, than the steps on Calabazas, representing the steeper channel slopes on Asbury. The one significant potential fish barrier on Calabazas is the 14.5 foot high waterfall carved in bedrock just downstream of the confluence of the north and south forks of Calabazas. This barrier is significant enough that we ended our survey for limiting geomorphic factors for fish migration at the confluence just upstream of the waterfall. E-8

13 Sedimentation Both Asbury and Calabazas creeks have a bimodal distribution of bedload, meaning they transport sediment that may be divided into two distinct size classes. Both creeks are boulder and cobble dominated over the majority of the channel. Most bars on both channels are cobble dominated. Few bars of medium to small gravel exist on Asbury, whereas Calabazas has more deposits of large, medium and small gravel. The mobile bedload fraction on Asbury is usually small gravel and sand. Pools on Asbury are dominated by fine sediment and organic debris throughout the length of the channel. The mobile fraction of bedload on Calabazas, in contrast, includes large and medium gravel in some reaches in addition to small gravel and sand over the majority of the channel. The pools on Calabazas contain much less organic debris than on Asbury and appear to contain coarser substrates. On Asbury the top of bank and bankfull were nearly indistinguishable in the upper reaches of the watershed. We began differentiating between bankfull and top of bank two down closer to Sonoma Creek off of Arnold Drive by the private residences where a floodplain first became identifiable. Due to the well-developed floodplain along the course of Calabazas, we were able to distinguish between top of bank at the floodplain for the entire survey. The well-defined floodplain, bars and discernable overbank deposits on Calabazas provide storage of finer substrates. On Asbury, fine material is stored in the channel. Note that on the long profiles (Figures E-1, E-2, E-3), bedrock geology is indicated where outcrops were seen in the stream banks. The bedrock symbols in the chart do not indicate the size or elevation of the bedrock outcrops relative to the stream bed; instead the symbols are place markers to indicate the stream station at which the bedrock outcrop was noted in the streambank. The geology through which Calabazas Creek is incising ought to be a large sediment contributor, being Quaternary old fan (Qof) alluvial deposits over the relatively incompetent Petaluma bedrock formation. Calabazas creek may not be supply limited. In other words, there is enough bedload to transport that the stream is not mining the banks. The bedload is course and there appears to be adequate floodplain storage for fine sediment. The cobble bars and secondary backwater channels are evidence of channel storage. On the other hand, because the stream is bedrock controlled, during large flow events, the stream may be more likely to erode the streambanks instead of the channel bed. This would mine the finer sediments in the overlying Qof. These flow events, however, would also probably have the power to flush the eroded bank sediment out of the Calabazas system. These hypotheses would require modeling and further investigation. Correlation of Stream Morphology with Watershed-scale Landforms The landform unit boundaries delineated on the longitudinal profiles are from the gross scale landform unit map of the Sonoma Creek watershed created by Tessera Consulting in parallel with this study (See Map Plate 4: Landform Units, Sonoma Creek Watershed Limiting Factors Analysis, 2006). Based on a visual topographic map analysis, the watershed is divided into six landform unit classes based on relative degrees of topographic relief and contour conformity. The units of topographic relief (low, medium, high) are differentiated based on the relative proximity of contiguous contour lines. Units of similar relief are further divided into areas of conformal (or fairly uniform) and crenulated (or irregular) contour line patterns. This landform map could be further refined to differentiate areas of similar contour conformity and by geometric expression and patterns, such as arcuate, lobate, or serrated. The landform map includes a unit with differentiates the Quaternary alluvium associated with Sonoma Creek. E-9

14 The theory is that areas exhibiting similar types of contour uniformity and degrees of topographic relief may be dominated by similar geomorphic processes. The landform unit coverage may be more useful as a predictive tool for identifying areas subject to similar dominant geomorphic processes when analyzed in combination with other physical data, such as geology, soils, slope curvature, and aspect. Asbury Creek On the longitudinal profile of Asbury Creek, the stream reach associated with the landform map unit of high conformal relief is dominated by bedrock outcrops, cobble bedload, and large woody debris deposits. The stream reach through the landform unit of medium non-conformal relief contains multiple slope and bank failures. The slope of the stream is fairly regular. The stream channel appears to have four identifiable concave up segments. The contact between the two landform units is located at the contact of second and third concave up stream segments. This is also the location where two highly incised left bank tributaries enter the creek. Calabazas Creek On the longitudinal profile of Calabazas Creek, the stream reach associated with the landform map unit of high conformal relief is dominated by debris flow tributaries and loose boulder and cobble bedload. The stream slope is moderately uniform throughout this unit. This unit has the most natural occurring large woody debris in the stream channel. The upper unit of medium non-conformal relief is associated with a reach of stream that is dominated by boulder, cobble bedload and has multiple areas of bedrock expression in the channel. The banks in this reach average seven feet high and are comprised of the Glen Ellen formation overlain by Quaternary alluvial fan deposits. The stream slope is highly irregular in this reach. By contrast, the stream reach in the alluvium unit just downstream is relatively uniform and gentle. The stream reach in lower unit of medium non-conformal relief is located along the base of a hill. Whereas the stream is alluvial, it may be located at the contact of the alluvium and the medium non-conformal relief units on the landform map, and the resolution of the map did not allow for more accurate identification of the associated landform unit in this reach. The slope of Calabazas Creek is discernibly flatter in the Sonoma Creek floodplain unit. RECOMMENDATIONS FOR FURTHER STUDY Budget restrictions limited the amount of data analysis performed on this project. It is recommended that the data gathered on Asbury and Calabazas Creeks be more thoroughly mapped, graphed, tabulated, and analyzed to derive the maximum benefit from the fieldwork performed. Additional field studies are suggested to help answer questions prompted by the initial investigation. E-10

15 Water Budgets Prepare a water budget for Asbury and Calabazas Creeks. Explore the role of differential rainfall on discharge in the creeks. Specifically account for the timing of the installation of the siphon diverting water to Fern Lake, and calculate the percentage of water diversion accounted for by the siphon. The incision we are seeing on Asbury Creek, which may be related to watertable draw down, evidenced by the springs in the base of 8 foot high bank cuts; and which appears to have occurred since the time of redwood logging, evidenced by the bank incision beneath logged redwood trunks; may be due to drawndown of the watertable caused by siphoning of water off Asbury Creek to Fern Lake. There are no other apparent diversions from the creek which could account for the drop in water table. Also, if the drop in water table was from well draw down in the valley, why would we see incision above control points in the channel? Groundwater Dynamics Conduct groundwater studies and research the history of groundwater levels. Explore the causes of groundwater table lowering such as well pumping and stream diversions. Explore whether the drawdown of the groundwater table is influencing streambank failure or knickpoint migration in hillslope stream channels. Stream Flow Measurements Take stream flow measurements. Analyze the data to determine whether the stream is gaining or losing discharge along its length and for hydraulic models. Where possible, measure high water mark depths and correlate to known storms to derive a stage discharge rating curve. Conduct field studies at equal intervals during the water year to map wet and dry reaches of stream to garner a better understanding of channel flow sources such as springs, irrigation, and lake overflow channels. Watershed-scale Landform Influences Using the watershed-scale landform map of the Sonoma Valley prepared in parallel with this field investigation, examine more closely the relationship between changes in large scale landforms and changes in stream morphology. Note that some landforms may be the result of relic processes and may not reflect current processes. Assess whether and how the stream is adjusting in relation to relic and current land forming processes. Digitize the gross scale landform map to explore watershed-scale influences on the stream channel network. Include boundaries of historic water bodies, such as the San Francisco Bay and Kenwood Marsh. Subwatershed Landform Mapping The existing field and map data could be translated into a finer scale geomorphic map of landforms being formed by current processes. This would refine estimates of erosion potential and site-specific linkages to habitat quality. For example, the mountain-scale landslide in the Asbury Creek watershed, a prominent relic landform, is no longer the dominant erosional process. However, slopes on the relic slide may be more susceptible to erosion than others in the park. Therefore we recommend this data be used to produce a finer scale geomorphic map, including a map of subwatersheds to indicate flow of water and sediment in the watershed. A slope or curvature map demonstrating erosional and depositional zones in the subwatersheds, generated for this project in GIS, could be used to better define the route of sediment flow. Include mapping of shallow debris slides and earthflows from air photo interpretation and field verification. Analyze the distribution of slides to help predict where slides might be located E-11

16 throughout the rest of the watershed. Use this data to assist in the preparation of watershed and channel scale sediment budgets and a model for predicting habitat type and value. Landslide Map Analysis There is an existing landslide map of the Sonoma Valley watershed which could be scanned to compare with landslides and slope failures mapped in the field. Composite landslide coverages throughout the valley can be used to compare with a GIS generated slope curvature data layer to test whether the curvature-predicted landslides are associated with actual mapped slide areas. Complementary Fieldwork Accurately map faults, bedrock contacts and fractures to better explore the relationship between these factors and stream slope changes as well as the distribution of watered and dry reaches of stream channel. E-12

17 Table E-1. Summary of Geomorphic Attributes of Two Representative Tributaries ASBURY CREEK CALABAZAS CREEK Fish Habitat Quality Fish Habitat Quality Relatively Poor Relatively High Watershed Watershed Total Elevation Range:220 - Total Elevation Range: Elevation Range Mapped: ft Elevation Range Mapped: ft Elevation Change Study Area: 620 ft Elevation Change Study Area: 440 ft Stream Length Mapped: 12,900 feet Stream Length Mapped: 20,900 feet Stream Gradient Mapped Area: 5% Stream Gradient Mapped Area: 2% Hydrology Hydrology Small Drainage Area: 1.1 sq.mi. Large Drainage Area: 12.6 sq.mi. Less Discharge / Stream Power More Discharge / Stream Power Dry Stream Reaches Perennial Along Reach Higher Percent of Water Diversions Lower Percent of Water Diversions Precipitation: To be Determined Precipitation: To be Determined Channel Morphology Channel Morphology Little to no floodplain Well-defined floodplain Step-Pool Pool, riffle, glide Narrow, confined channels Secondary and backwater channels Poorly Sorted Channel Substrate Well-Sorted Channel Substrate Few Gravel Bars Gravel Bars / Sediment Storage Pools Filled with Fines and Organic Debris Pools Filled with Coarser Sediment Narrow, V-Shaped Canyon Wide, Box Canyon Most incised in Middle Reach Incised in Sonoma Valley Fan Only Sediment Load Sediment Load Boulder-Cobble Dominated Bed Boulder-Cobble Dominated Bed 9% Gravel Bed Material 7% Gravel Bed Material Higher Percentage of Fine Sediment Lower Percentage of Fine Sediment Sediment Sources Sediment Sources Unstable Banks Stable Banks One Debris Flow Tributary Multiple Debris Flow Tributaries Channel Bank Slope Block Failures No Channel Bank Slope Block Failures Substrate Substrate Tertiary Volcanic Flow Rocks Tertiary Volcanic Flow Rocks RELEF UNITS: High Conformal; Medium Non-Conformal RELEF UNITS: High Conformal; Medium Non-Conformal; Alluvium; Sonoma Creek Floodplain Relic Hillside Scale Landslide, Joints, Faults Joints and Faults Channel Obstructions Channel Obstructions Natural Fish Barriers One 15 ft. high Natural Fish Barrier Two Constructed Fish Barriers One Constructed Fish Barriers Impassable Large Woody Debris / Log Jams Passable Woody Debris Land Use / Cover Land Use / Cover Historic Extensive Redwood Logging No Evidence of Extensive Logging Currently Closed Woodland Currently Majority Closed Woodland E-13

18 Figure E-1. Asbury Creek, River Stations 0-14 October 2003 Long Profile Legend Figures E-1, E-2, and E-3 Road Stone Abutments RB Bridge Abutment Stream Landform Unit Extent Bedrock-Channel Bed Boulder-Channel Bed Cobble-Channel Bed Gravel-Channel Bed Sandy-Channel Bed LWD Qof White Tuff Rhyolite Rhyolitic Soda Flow Glen Ellen Fm Landslide Elevation (feet) W E 200 HIGH CONFORMAL RELIEF MEDIUM NON-CONFORMAL RELIEF River Station (feet) E-14

19 Figure E-2. Calabazas Creek, River Stations 0-21 November 2003 Quarternary Old Fan (Qof) over Glen Ellen Fm North fork Calabazas bedrock waterfall Dirt road fork at gate Elevation (feet) RB Tributary Bridge at the Smiths Bridge at 1210 Dirt road ford W E FLOOD PLAIN MEDIUM NON- CONFORMAL RELIEF ALLUVIUM MEDIUM NON- CONFORMAL RELIEF HIGH CONFORMAL RELIEF River Station (feet) E-15

20 700 Elevation (feet) Figure E-3. Calabazas Creek, River Stations 9-19 November 2003 Bridge at the Smiths Quarternary Old Fan (Qof) over Glen Ellen Fm Bridge at 1210 Dirt road fork at gate Dirt road ford River Station (feet) E-16

21 REFERENCES Montgomery, D. R., and J. M. Buffington Channel classification, prediction of channel response, and assessment of channel condition. Report. No. TFW-SH Prepared by Department of Geological Sciences and Quaternary Research Center, University of Washington, Seattle for SHAMW Committee of the Timber/Fish/Wildlife Agreement, Washington Department of Natural Resources, Olympia. Montgomery, D. R., and J. M. Buffington Channel-reach morphology in mountain drainage basins. Geological Society of America Bulletin 109: Montgomery, D. R., and J. M. Buffington Channel processes, classification, and response. Pages in River ecology and management, R. J. Naiman and R. E. Bilby, editor. Sprnger-Verlag, New York. E-17