Seeking Clarity: A New Vision for
By Shelly M. Rhoden
Before development, the large wetland surrounding the mouth of the Upper Truckee River, known as Truckee Marsh was an outstanding wildlife area and also functioned as a major filtering system for water flowing into Lake Tahoe. Over the last four decades, the land was changed with a vision of development, affecting the stability and condition of the river and wetland.
For example, in the late 1 950s the lowermost 2,000 feet of the river was channelized as part of the development of the Tahoe Keys. A 23-acre area along the west river bank was also filled with four to six feet of sandy soil, covering a historic wetland. These changes, over time, created a negative environmental impact on the area. The Upper Truckee River drains over 30 percent of the land area of the Lake Tahoe Basin and as the wetland area was depleted, the largest single source of sediment filtering for water entering Lake Tahoe was diminished. Overall, the Lake Tahoe Basin has lost 75% of its marshes, 50% of its meadows and 35% of its riparian habitat. Restoration of wetlands and areas has been identified as a major priority of the Environmental Improvement Program (EIP) adopted by the Tahoe Regional Planning Agency (TRPA) and other resource agencies in the basin. The California Tahoe Conservancy (CTC), a state agency whose goal is to purchase and restore environmentally sensitive land, has been at the forefront of restoration efforts, restoring wetlands and creeks on the California side of the basin since 1985.
The Upper Truckee River and Wetland Restoration Project/Lower West Side (LWS) component was developed to restore over 11 acres of wetland within a 23-acre portion of the Upper Truckee Rivers historic floodplain, protecting and improving the water quality of Lake Tahoe. Located at the mouth of the Upper Truckee River in the City South Lake Tahoe, the project site includes 208 acres with more than 1,400 feet of lakefront The land was acquired by the CTC in 1988 and is located on both sides of the river and east of the Tahoe Keys Marina.
The design criteria for the LWS Project was based on an assessment of complex, lake-driven hydraulics in the river delta and stream flow conditions. Plans for the project called for fill removal, grading and revegetation, construction of public access paths, entrance improvements, interpretive signage, traffic control, an irrigation system (including wells) and erosion control. The CIC partnered with the CA Department of General Services, Real Estate Services Division, Entrix (engineering services lead) and EDAW, Inc. (environmental services lead) to develop and complete the restoration plan.
One of the Key elements of the project was the disposal of the fill material. During design development, there were a few sites within the Lake Tahoe Basin that were under consideration; however, as design and permitting progressed, the only feasible alternative was an out-of-basin site requiring a six-hour round trip for the disposal of each load. Because the project site is located within the city limits and access was via US Highway 50 and Tahoe Keys Boulevard (a weight restricted road), intensive coordination with the City of South Lake Tahoe and Cal and a well thought out traffic control plan was critical for the success of the project.
Immediately preceding construction of the wetlands, a 5- acre former gravel quarry site on California Department of Parks and Recreation land became available as a fill-disposal site, in lieu of the 6-hour out-of-basin haul. The quarry site was within 5 miles of the project and provided an excellent opportunity to use the excavated material for restoration of an additional site within the basin. By working closely with all concerned agencies, the project team was able to produce the plans, specifications and obtain the necessary permits within only a few months time. allowing both restoration projects to proceed concurrently and without delay.
The first phase of construction, the excavation and restoration of the wetland, began in May 2001, ‘with Entrix providing construction supervision services. Gordon N. Ball, Inc., the primary contractor on the project, removed 82,400 cubic yards of fill from the site between June and August 2001 and re-formed the landscape to a condition more like its predevelopment state.
The equipment used was a Cat 345 B excavator, Komatsu/Cat D4HITD8 dozers, Case 580 backhoe, Cat 140 G Blade, Cat 623 F scraper, and 4,000- gallon water trucks to provide dust control. The low lake level helped the excavation tremendously, since no dewatering was required. In October, topsoil that had been provided from the Trout Creek Restoration project in South Lake Tahoe was hauled into the LWS restoration area and incorporated into the soil to assist with revegetation efforts.
Phase Ill of the project included the replacement of an existing earthen berm along the newly constructed wetland, additional grading and contouring work, irrigation and continuing revegetation work. The subcontractor in charge of revegetation was Bitterroot Restoration, Inc. and Sierra Nevada Wilds was the sub in charge of installing the irrigation system. Equipment utilized in these portions of the project included a skip loader, V41 50A trencher, hydroseeder, Bobcat with loader, quad with harrower, shred vac equipment for wood mulching, an asphalt paver and double drum roller to install the decomposed granite public access path.
The lower elevations were planted with native wetland plugs that were adjacent to the project area. Following the incorporation of salvaged soil, 32,500 plugs were planted on an average 3.5-foot center throughout the wetland area. Sod containing rushes sedges, grasses or a combination thereof, was harvested from the project site prior to Phase land II construction activities and reserved for planting. Following the incorporation of native soil, the sod was replanted in specified areas with an intended total of 26,000 square feet for Phase I and 9,000 square feet for Phase II. The plugs and salvaged sod for Phase I were planted in the fall of 2001. The sod salvaged during Phase 11 was planted in the fall of 2002.
In addition to the plug and sod planting, direct seeding of native herbaceous wetland species was prescribed for the 11 acres of wetland during Phase land later for the additional acres excavated during Phase II. After the seedbeds were prepared, seeds were directly broadcast over the site and blended into the soil, For Phase I, two sources of seed were available; (1) a commercial seed mix, and (2) a seed mix collected from local Tahoe Basin sources. Phase I seeding with both seed mixes took place in the fall of 2001. A total of 18 pounds per acre of commercial wetland seed mix was used for direct seeding on site. Local seed mix available for use on site was 62.75 Pure Live Seed (PLS) pounds of commercial seed prior to spreading, In the fall of 2002, Phase I- seeded a total of 23.4 pounds per acre using native collected seed only with similar PLS and weed free requirements as Phase I.
Direct seeding of native herbaceous and shrub species was prescribed for the remaining 11 acres of non-wetland at the site. A targeted total of 24.25 pounds per acre was spread at the site during Phase I in the fall of 2001. As well, 8.5 lbs. of the local native seed mix was mixed with the commercial seed prior to spreading it in the upland areas. A total of 26 pounds per acre of commercial upland seed mix, which included three additional species of wildflower mixed in, was spread on all disturbed upland areas for Phase II in the fall of 2002. Following the seeding, mulch and tackifier were applied in the upland/transitional zone for temporary erosion control.
Many willow species are well adapted to wet conditions and their deep extensive root systems provide for the stabilization of slopes and banks. To consolidate and stabilize soils along the newly contoured slopes on site, willow stakes were installed within the transitional zone between the upland and the wetland. The willow stakes were cut from shrubs located within the project site. The stakes include Lemmon’s willow (Salix lemmoniz), Shining willow (S. lucida) and Geyer’s willow (S. geyeriana). Lemmon’s willow is the most common willow found near the site and cuttings that were taken for the stakes are predicted to be predominately S. lemmonii. Fifteen hundred willow stakes were installed on April25, 2002. During Phase Il, 56 willows were salvaged from the excavation areas and planted along the toe of the newly restored wetland, and open-weave coconut fiber erosion control blankets were used on the more vulnerable seeded slopes. A small area within the restored wetland near the southwestern end, approximately 40 feet by 40 feet, was neither seeded nor planted. This test plot will be used to investigate recruitment by native vegetation at the site without intervention.
The removal of fill has reestablished site elevations which favor sod saturation or shallow inundation under most conditions, sustaining a diversity of wetland plant communities. As a result, a portion of the natural water treatment capacity lost when the original wetland was disturbed will be restored. The potential for nutrient uptake and filtering of suspended sediment by vegetation, groundwater recharge and microbial dentrification will be increased. In addition, restoration of the site will enhance habitat for birds and mammals. The restored wetland will be similar in topography hydrology and habitat characteristics to the existing wetland east of the Upper Truckee River.
According to permit conditions, a 3 to 4 year plant establishment period was required at the wetland site to protect water quality of the lake. After that time, and with the approval of the TRPA and the Lahontan Regional Water Quality Control Board, the final phase of the project will reconnect the wetland with the Upper Truckee River/Marsh system. In order to do this, the earthen berm isolating the wetland would have to be excavated to allow direct interaction between the lake, river and wetland. Entrix’s innovative approach to replace portions of the earthen berm with three AquaDams, temporary water-filled dams, allowed excavation of the earthen berm to take place in 2002, taking full advantage of the lower than normal lake levels. After the plant establishment period, the temporary dams will be roiled up and removed without unnecessary impact to the approach allowed construction to be completed two to three years sooner than expected. Complete details about the temporary dam construction can be found at www.aquadam.us
Entrix’s design team produced the additional plans and specifications for this phase of the project within a few months time and acquired additional permits, including authorizations from the US Army Corps of Engineers, California State Lands Commission and the Federal Emergency Management Agency.
Washoe Meadows Restoration
The CTC provided funding to the California Department of Parks and Recreation for revegetation of the Washoe Meadows Quarry pit. The revegetation of the pit area took place in August 2002. The work included decompaction of the fill to a depth of eighteen inches, use of composted pine needles to increase organic matter content of the fill, seeding with upland native plants, the application of pine needle mulch and the placement of large woody debris. Upland trees and shrubs were planted in the fall of 2002.
Entrix continues to provide construction supervision and site monitoring during the contractor maintenance period, which extends through January 2004. The Entrix team is currently developing and implementing a monitoring program to assess the overall effectiveness of the project to improve water quality.
Restoration of the Lower West Side Wetland site is anticipated to take three years for completion (2001-2003). The site’s physical modifications and the first and second phases of the revegetation plantings took place in 2001 and 2002. Replacement planting, as necessary, will take place in 2003. Revegetation monitoring was initiated by EDAW in the summer of 2002.
Improving Lake Tahoe’s clarity is a large, complex job and no single activity will suffice. Revegetation of bare soils is needed throughout the lake’s 64 watersheds. Runoff from streets and parking lots needs to be trapped and cleansed before it reaches streams or the lake. More research is needed to understand the role of air pollution, shoreline erosion and other factors. And, knowing that some sediment and pollutants will still find their way into the waterways, stream courses and their adjacent wetlands need to be restored. As much sediment and nutrients as possible need to be trapped moved before they reach the lake.
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