UNITED STATES
DEPARTMENT OF THE INTERIOR
BUREAU OF LAND MANAGEMENT
Redding Management Area (RMA)
REDDING FIELD OFFICE
355 Hemsted Drive, Redding, CA 96002
HYDROLOGY REPORT
Project Name:
LOWER EAST WEAVER
HABITAT IMPROVEMENT PROJECT
Prepared by: /s/ Mark S. Lancaster
CA Registered Professional Forester
Five Counties Salmonid Conservation Program
Northwestern California Resource Conservation and Development Council
Reviewed by: /s/------
Redding Regional Office
June 15, 2012
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East Weaver Creek Fish Habitat Improvement Project - Hydrology Report – May 15, 2012
I. Description of Proposed Project
The Five Counties Salmonid Conservation Program (5C)[1] in cooperation and partnership with the Weaverville Sanitary District (WSD), Bureau of Land Management, Trinity River Restoration Program, and Trinity County Resource Conservation District proposes fisheries restoration activities in East Weaver Creek, specifically to install in-stream large wood/boulder habitat elements, lay back an over-steepened stream bank and bio-engineer a new bank. The project will enhance fish habitat and protect the WSD’s largest capacity sewer main, which runs under the stream within the project area. East Weaver Creek has long been recognized by the 5C as being deficient in both transporting and recruiting large diameter wood and the Program has sought ways to provide this critical fisheries habitat element to the stream. This project provides that opportunity.
Between 1997 and 2006 East Weaver Creek shifted its active channel[2] 80’ west and 300’ upstream of the WSD sewer main and in the process exposed portions of the line, increasing the risk that the sewer main could be damaged in high flows. Prior to the channel shift the WSD line within the active stream channel was protected by an 18” thick concrete ramp. That ramp, while protecting the sewer line, created an upstream migration barrier for juvenile fish in all flows and a partial barrier for adults in low flows. The stream channel shift eliminated the concrete ramp as a migration barrier.
The project is located in the East Weaver Creek -Trinity River 7th-field subwatershed and East Weaver Creek is a fourth-order perennial tributary to the Trinity River (Table 1). The project is located in on the boundary of Section 18, T33N, R9W, and Section 13, T33N, R10W ,MDBM (Weaverville Quadrangle) and runs from approximately 100’ downstream of the confluence of East and West Weaver Creeks to upstream approximately 1,020’ (RM 0.193). Weaver Creek’s channel and floodplain morphology, including the project area has been modified by historic gold dredging (refer to Figure 1). Subsequent to the mining, the channel was straightened and a levee was construction following the 1964 flood. These activities have significantly disrupted natural large wood recruitment and routing processes as well as natural fluvial and morphological development of the channel.
Table 1. East Weaver Creek Fish Habitat Improvement Project watershed hierarchy
Level / Code / NameHUC8 (Subbasin) / 18010211 / Trinity River
HUC10 (Watershed) / 1801021107 / Weaver Creek-Trinity River
HUC12 (Subwatershed) / 180102110705 / Weaver Creek
The project would install two stream elevation wood/rock structures (SEW/RS) downstream of the WSD sewer main. These structures would span the active (2-year flow) stream channel. The SEW/RS will be set in a “V” configuration with the lowest point forming a 6” drop during low flow (<10 cfs) channel conditions. These structures will allow upstream accumulation of channel bedload over the currently exposed sewer line. The logs will provide resting cover and habitat for fisheries, while also preventing channel downcutting. Large rock (1-2 ton) ribbons will be set below the channel bottom tying into the logs. Upstream of the sewer main two wood/rock groin structures will be installed in the right bank[3] to deflect high flow energy to protect the banks as well as increase resting and low flow habitat. Approximately 100 feet of the stream bank, beginning 30’ downstream to 70’ upstream of the sewer main, will be laid back from the current ½:1 slope to a 3:1 slope and stabilized using bio-engineered rock slope design. A rock ribbon will be placed approximately 150’ upstream of the sewer main and set outside of the 5-year floodplain in order to protect the restored stream bank during high flow flood events. A root wad structure will be embedded on the left bank (~5-year floodplain) approximately opposite of the rock ribbon structure to encourage an active avulsion, directing high flows into the left (historical) stream channel.
The project will enhance habitat for anadromous salmonids, including coho salmon[4] (Oncorhynchus kisutch), a federally and state listed Threatened species; steelhead trout[5] (Oncorhynchus mykiss); and Chinook salmon[6] (Oncorhynchus tshawytscha). Other fisheries species of the area include lamprey (Entosphenus tridentatus and Lampetra sp.), Klamath small-scale sucker (Catostomus rimiculus), and specked dace (Rhinichthys osculus). Bio-engineered bank stabilization and large wood placement will have the added benefit of protecting the sewer riser (a vertical pipe extension for access to a buried sewer line running underneath the creek) by preventing the creek from further eroding the stream bank. Should the pipe be damaged, as much as one million gallons per day of untreated sewage may enter the Creek. In addition stream inflow into the damaged sewer main could impact operations at the sewer plant until the line could be plugged. Additionally, placement of structures in the active channel will prevent additional scour of the creek and stabilize the creek gradient through the project area. Placement of large wood debris (LWD) will create habitat that otherwise would take decades because of the lack of significant numbers of recruitment large wood.
Figure 1. Undated photo of Weaver Creek shows the effect of mining on stream morphology and wood recruitment. The arrow identifies the project reach.
Between 1850-1950, East Weaver Creek was mined for gold. The mining mobilized and washed away a significant portion of the smallest particles (clay, sand, silt, small gravel) and left larger diameter particles to form the bed and banks. Channel banks and floodplains were rebuilt with tailings and the floodplain was widened while the channel gradient was lowered. The course bedload, channel gradient and floodplain conditions are more similar to glaciated stream channels then the steeper gradient channels observed in similar Weaver Creek tributaries such as Little Browns Creek (although there are no stream reaches that do not show evidence of past mining, few have been as significantly disturbed as Weaver Creek in this reach). In 1965 the Army Corps of Engineers constructed a levee on Weaver Creek approximately 0.4 miles upstream of the confluence with West Weaver Creek. The levee has further disrupted natural hydraulic and biological processes.
Weaver Creek is designated as critical habitat for threatened coho salmon by NOAA’s National Marine Fisheries Service (NMFS) and as a tributary to the Trinity River, it is designated as impaired by excess sediment and siltation under Section 303(d) of the Clean Water Act by the State Water Resources Control Board. There is an EPA-approved sediment Total Maximum Daily Load (TMDL) in place for the Mainstem Trinity River system (EPA, 1999). The project area, located within 300 feet of a fish-bearing perennial stream (Weaver Creek), is within designated Riparian Reserves under the Northwest Forest Plan (NWFP) and the Bureau of Land Management Resource Management Plan. All proposed project activities will meet the Aquatic Conservation Strategy Objectives. Additional details regarding application of all applicable environmental laws and regulations are provided in Section IV below.
Figure 2. Project Location Map
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East Weaver Creek Fish Habitat Improvement Project - Hydrology Report – May 15, 2012
Figure 3. Crossing (#1 and #2) Locations
Figure 3 (photos above). Confluence of West and East Weaver – location of Large Woody Debris placement (left); Sewer riser, pipeline and apron crossing East Weaver (center) and High flow channel upstream of pipeline (right).
Figure 4 (photos below). Bioengineered streambank on a nearby comparative watershed (Little Browns Creek at Roundy Road). The left photo is similar to the proposed streambank to be installed at East Weaver Creek. A rock and log groin similar to what will be installed in East Weaver Creek is pictured to the right.[7]
II. Field Evidence- East Weaver Creek Watershed Scale
Field Observations and Data Collection
The Federal Emergency Management Agency (FEMA) completed a FIRM Flood Insurance Study of Weaver Creek in 1989 and revised the plat map in 2010 to correct elevational errors in the Sidney Gulch watershed.
A stream condition survey has not been completed, but empirical observation in 2011 and 2012 noted only three large pieces of wood (>16” DBH on large end and longer than 20’) within the lower 0.4 miles of the active channel and only limited recruitment of downed wood or even standing bank trees of this diameter. Additionally, there is minimal potential for large wood routing through the Army Corps maintained levee upstream of the project.
Thalweg/Cross Section Survey
A thalweg and cross section survey of the project area was conducted by Ross Taylor and Associates and 5C staff in April 2011. The survey consisted of 1,021 feet of channel from the confluence of East and West Weaver Creeks (RM 0.00) upstream 1,021 (RM 0.193). The survey extends at least 100’ upstream of the upper end of the project area. In addition seven cross sections were surveyed within the project reach and were spaced 30 to 100 feet apart to reflect horizontal and vertical changes in the channel geometry within the reach area.
Geomorphic Mapping
A geomorphic assessment of the project area included a walk-through of the site, photo-documentation, measurements of the active channel, observation of other geomorphic channel expressions (including topographic benches, side/diversion channels, etc) and review of the delineated floodplain based on FEMA FIRM mapping.
Approximately 0.5 miles upstream of the confluence the channel is confined in a levee section where vegetation growth is controlled. On either side of the levee urban development has replaced natural forests. There are no natural debris recruitment processes upstream and the lack of large wood in the channel influences its plane form for more than a mile upstream of the confluence with West Weaver Creek. The levee channel segment provides substantially less in-stream and riparian habitat diversity. It is much straighter than the downstream segment. The channel corridor width is substantially narrower than downstream, with widths ranging from 50 to 80 feet. In comparison to the project reach, this levee segment upstream has more cobbles and boulders in the channel bed. There is little downed wood within or adjacent to the stream channel and few gravel depositional features. Water depths are deeper and the channel is highly entrenched with no available floodplain at higher flow events. This creates higher in-channel shear stresses and sediment transport competence at lower flows than the downstream channel segment. The observed increase in channel bed material size and lack of depositional features suggests that smaller gravels delivered from upstream are transported through this channel segment. The lack of large wood influenced habitat, well aggraded bedload materials, lack of canopy cover and higher velocities reduce the quantity and quality of fisheries habitat in this reach.
The stream channel, adjacent banks, and floodplains in, and upstream, of the project reach consist of alluvium modified by hydraulic mining and is not reflective of the natural bedload transport condition (refer to discussion above). The channel lacks fines that were washed away in the process of gold mining (refer to Figure 1). The net effect is a channel that approximates a glacial influenced stream condition with very course gravel and cobble dominating the stream bottom. The lack of fines in the banks and overbank areas limits available soil moisture which in turns reduces the extent of natural forest vegetation as compared to unmined stream banks. The lack of large trees combined with the upstream disruption of natural recruitment processes has resulted in relatively simple riffle/run complexes in the project area.
The active channel of winter 2011-12 was readily identified by a unique fine clay silt deposit that is new to the stream. This silt resulted from a large landslide in the East Branch watershed that produces this uniquely textured and colored clay layer. The grey silt line provides an excellent delineator of the year’s flows. The March 2012 flow line is estimated to represent a 1.2-year return interval flow based on gauge monitoring being done by Graham Mathews and Associates for the 5C Program in the adjacent Sidney Gulch watershed. The estimate return interval for the flow correlates well to observed small topographic benches and side channels with annual herbaceous grasses. The 2010-11 winter flows were estimated to be a 2-year event, again based on monitoring work in the adjacent Sidney Gulch watershed. The flow line from that storm was apparent during the field site review as delineated by debris lines and litter accumulations. A series of benches/breaks in slopes and overflow channels combined with willow/cottonwood/alder trees and shrubs provide indication of the approximate 5-year flow line.
The active channel width varied from 10 to 45 feet, averaging approximately 23 foot.
The streambed is composed of very coarse gravels to small cobbles with occasional small boulders.
Hydrology
East Weaver Creek is a fourth order watershed and the largest tributary to Weaver Creek. East Weaver Creek watershed elevations range from 7,771’ at Monument Peak to 1,950 feet at the confluence with West Weaver Creek. The watershed is a snow melt runoff system with rain-snow transition in the 2,000-4,000 elevation band. The snowmelt recharged system provides cold year round flows down to the diversion dam for the Weaverville Community Services District domestic water supply intake (Section 30, T34N, R9W, MDB&B). The contributing drainage area to the project reach is 13.0 square miles, with the majority of the watershed within the Shasta-Trinity National Forest.
Nearly all of the upper 70% of the East Weaver Creek watershed consists of Klamath Mixed Conifer with inclusion of Montane Hardwood woodlands generally on south facing slopes and in areas with shallow soils. Subalpine fir forests occur at the highest elevations. Approximately 59% of the 8,300 acre watershed is within the Trinity National Forest and approximately 29% is within the Trinity Alps Wilderness. The lower 20% of the watershed consists of semi-urban Weaverville (population 3,500) and another 20% consists of rural residential uses intermixed within mixed conifer forests. Sierra Pacific Industries (SPI) owns 684 acres intermixed with the National Forest lands in the upper end of the watershed.