Res 2003-152 - Laserfiche WebLink

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water pumped from the San Marcos River. Aquatic vegetation, within each retention pool will be native and taken from the nursery established by the Wetland Project at Aquarena Center and approved by the U.S. Fish And Wildlife Service (USFWS) prior to planting. Native bulrushes, pickerel weed and other types of native aquatic plant species will be used. Native grasses may also be established between pooled areas to create grass -lined swales along the drainage ditch to enhance soil deposition and nutrient removal. A temporary silt fence will be established around each construction area to minimize runoff and comply with National Pollutant Discharge Elimination System (NPDES) requirements. The silt fence will be monitored daily and the construction area will be covered with a tarp in the event of rain. An existing retention pool is located adjacent to the gristmill water control structure within the Rio Vista Dam park area (Enclosure 7, Photo 16). The existing retention pool consists of an approximate 0.2 -acre area that collects drainage from Cheatham Street prior to entering the gristmill channel and the San Marcos River. Enhancements to the existing retention pool area will include expansion of the pool through excavation, creation of a hydrologic connection with the gristmill channel and native aquatic plantings. Native grasses, forbs, and shrubs will be planted along hardpan surfaces adjacent to the river to promote filtration of polluted runoff from these surfaces (i.e., parking lots, river walk trails, high traffic areas, streets and railroad crossings). Native tree, shrub and grass species will be planted along hiking trail areas prone to high amounts of foot traffic to reduce vegetation and soil impacts (Enclosure 7, Photo 10). Vegetation planting along hiking trails will need to be planned in accordance with existing city crime prevention ordinances. Two open space areas located near Purgatory Creek (Enclosure 7, Photos 11 -12) will also be re- vegetated with native grasses and forbs to enhance filtration capacity and habitat diversity within the riparian corridor (1.0 acre). Near the Children's Park- Playscape area, approximately l .0 acre of highly compacted soil will be replaced with 6 -18 inches of topsoil and re- vegetated with native shrubs and grasses to reduce erosion, soil compaction and foot traffic (Enclosure 7, Photo 3). Approximately 30,000 cubic feet of topsoil will be required in various areas within the study area to restore eroded and compacted soil. Temporary chain link or post and cable fencing will be required along restored grassland areas and along trails to protect newly planted vegetation from damage due to local foot traffic. Fencing will be required until the vegetation becomes established and self - sufficient. (4) Sediment Removal: Riverbank erosion, increased surface runoff from hardpan surfaces and the lack of functional riparian corridors within the watershed have promoted the inflow of sediment into the San Marcos River. Soil laden flow has resulted in the formation of sediment bars at various locations within the San Marcos River; particularly near tributary confluences and storm water drainage ditch outflows. This degradation has negatively impacted native fish, macro invertebrate and mussel species within the river by decreasing available spawning, rearing and feeding habitat, as well as overall aquatic diversity. The City of San Marcos proposes to remove accumulations of silt on the river bottom at various locations from City Park to Rio Vista Dam by using a Sediment Vacuum Truck (SVT). Divers will section off and stake a 400 square foot section for sediment removal prior to commencement of work. Silt removal for the 400 square feet section is estimated to take approximately two hours each day. Silt will be suctioned from the bottom of the river .J