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4we plant species; and maintenance of soil dredging equipment. Annual O&M costs are estimated at $59,000 and are the responsibility of the City of San Marcos. b. Existing Conditions. The project study area is located within the transition area of the Edwards Plateau and Blackland Prairies vegetation regions and comprises an area of central Texas commonly known as the Texas Hill Country. Topography of the region is comprised of many springs, stony hills, and steep canyons, with variation in elevation from 900 to 2600 feet above sea level. Average annual precipitation ranges from 15 to 34 inches, with peak rainfall amounts in May, June and September. The subsurface geology of the Edwards Plateau is honeycombed with thousands of caves and underground lakes known as the Edwards Aquifer. Climax vegetation is composed primarily of big bluestem, switchgrass, Indian grass, wildrye, curly mesquite and buffalograss. The upland areas of the region support a variety of species including Ashe juniper, live oak, Texas red oak, Texas ash, post oak, Shinnery oak and mesquite. Trees in the bottomland areas are mainly American elm, cedar elm, Texas sugarberry, burr oak and green ash. In well- watered bottomland zones the woodlands are comprised of pecan, walnut, cottonwood, sycamore, bald cypress, black willow and several kinds of shrubs and vines. Rare plants within the region include the Tobusch fishhook cactus, Texas snowbells, rock quillwort and basin bellflower. Several reaches of the San Mareso River within the project study area contain the endangered Texas wild rice. The area hosts many species of resident and migrant birds including the endangered golden - cheek warbler and black- capped vireo. The project study area is located in the Central Flyway migration route for many wading and shoreline birds, waterfowl and Neotropical songbirds. The study area is also in the path of the Monarch Butterfly migratory flyway. Mammals known to live in this environment include the white- tailed deer, raccoon, javelina, Brazilian freetail bat, r'ingtail, nine- banded armadillo, cottontail rabbit and many small rodents. Numerous rare species associated with the San Marcos River include the San Marcos salamander, Texas blind salamander, San Marcos gambusia, and fountain darter. The San Marcos River and associated tributaries have experienced aquatic ecosystem degradation due to a variety of anthropogenic factors. Impoundment of water upstream and within the study area has altered the normal flow regime of the San Marcos River. The native aquatic plant communities within the San Marcos River have been displaced by invasion from exotic and generalist plant species. Increased nutrient and sediment loads from overland surface flow, tributary runoff, non -point sources and storm water drainage have reduced water quality and in- stream habitat values within the river. The majority of the bottomland plant community within the study area is highly disturbed and fragmented due primarily to urban encroachment, installation of hardpan surfaces, recreational disturbance and invasion of non - native plant species. This degradation has resulted in the loss of high quality in- stream and riparian habitat for plant and wildlife species within the study area. The proposed restoration plan will help restore aquatic and terrestrial habitat that has degraded due to human activity, including critical habitat for the Texas wild rice. c. Major Project Features. The preliminary restoration plan will include project measures that utilize and enhance existing aquatic, riparian and wetland features that have degraded along and within the San Marcos River. The proposed aquatic ecosystem restoration project 0a