Res 2003-152 - Laserfiche WebLink

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4 -6) are out competing native aquatic plants such as the fanwort, arrowhead and endangered Texas wild rice, which occur in small populations within the study area. Aquatic vegetation restoration within the recreational corridor will consist of manual clearing of exotic plant species from the top 1.0 foot of the water column through the use of divers (SCUBA and snorkel) in areas that are a minimum of three feet in depth. For areas that are between 1.0 and 3.0 feet in depth, the top 6.0 inches of vegetation will be removed. Two divers, using scythes, will cut the vegetation and place it into collection bags to be later discarded in an offsite landfill area. Clearing will be limited to 100 feet of river length within the recreation corridor per day. Cleared areas will be propagated with native low- growth vegetation such as Texas wild rice (state and Federal listed endangered species that is endemic to the study area) (OMIT THIS), arrowhead, and fanwort through transplantation efforts, and existing wild -rice stand will be encouraged to expand (ADD THIS). Native plant species will be planted in cleared areas at about one per square foot. Trial runs have been performed and caging was not necessary to protect the plants from predation. The sites will continue to be "weeded" until the plantings are established. The replacement of exotic high - growth species with native low - growth species should decrease future O&M costs associated with aquatic plant clearing. The removal of elephant ear within the study area will not be addressed by the 206 Aquatic Ecosystem Restoration study. The City of San Marcos already has a City Master Plan in place to address the elephant ear infestation along this section of the San Marcos River. The aquatic vegetation restoration measure will replace approximately 3 -5 acres of exotic vegetation with low- growth native species that are locally endemic and more conducive to recreational uses. Benefits associated with aquatic vegetation removal and maintenance within the San Marcos River will include: increased water flow, improved recreational uses and expansion of threatened and endangered aquatic plant species. (3) Nutrient & Sediment Control: In- stream aquatic habitat within the study area has been negatively impacted by the inflow of nutrients and sediment associated with urban runoff during rainfall events. As a result, water quality has degraded, in- stream aquatic habitat has decreased and increased eutrophication has promoted invasive aquatic plant growth. Several nutrient and sediment control measures will be implemented within the study area including, but not limited to, installation of retention pools and low -water check weirs on adjacent storm drainage ditches and establishment of tall grass prairie areas adjacent to hardpan surfaces. The drainage ditches located within the City Park area on the northeast corner of Hopkins Street Bridge (Enclosure 7, Photo 7), along the southern boundary of the City of San Marcos Parks and Recreation building (Enclosure 7, Photo 8), and along the southwest corner of Hopkins Street Bridge (Enclosure 7, Photo 9) receive a large amount of street and hardpan runoff from the surrounding area. Low -water check weirs and associated retention pools will be installed on the three unnamed drainage ditches, approximately 50 to 200 feet upstream from the confluence with the San Marcos River to create pooled areas that decrease runoff flow, capture sediment and remove pollutants prior to water entering the San Marcos River. Weirs will be constructed of native stone or rock - filled gabions that are approximately three feet high and tied into both sides of the drainage bank. Soil will be excavated behind each weir and lined with plastic or clay to create a pooled area beneficial for sediment deposition and aquatic plant growth. Retention pools will be filled with no more than 1000 gallons of 2