OCR Text |
Show During the flood years, the causeway began to slough- off, settle and subside into the lake. It experienced five to six feet of subsidence along much of its length due to the weight of additional fill material. By spring 1984, very large inflows of freshwater into the south arm of the lake and restriction of flows to the north through the causeway fill, plus plugged causeway culverts, created a head differential of water levels. The higher elevation in the south arm added greatly to flooding problems on the south and east shores of the lake. The state constructed a 300- foot opening ( breach) in the causeway, just off the west shore near Lakeside, to allow the rising waters to flow more freely into the north arm, thus reducing the large head differential and flood damage. The plugged causeway culverts and extremely high inflow created a head differential of water levels of nearly 3.5 feet between the north and south arms. The breach lowered the head differential between the lake arms to less than one foot. Flooding Impacts on Recreation Due to record high water of the early 1980s, many millions of dollars of recreation facilities and user opportunities were lost. Antelope Island was isolated, marinas were forced to close and the southern sandy beaches were inundated by the waters of the lake. Recreation facilities on the lake generally begin to experience damage and interference with operations at lake levels of approximately 4205 feet and higher. Flooding Impacts on Wildlife and Wetland Structures Most WMAs around the lake were constructed in the 1930s to 1940s when lake level was relatively stable at 4198 feet above sea level. At these levels, annual production of waterfowl approached three- quarters of a million birds, with non- game production numbering in the multi- millions. Total bird use of the marshes on the lake exceeded 100 million use- days annually and recreationists would expend one- half million days each year afield. Marshes were managed for mean water depths of about 18 inches. During the flood years of the 1980s, nearly 300,000 of the 400,000 acres of marsh around the lake were inundated or devegetated due to salt water intrusion. Damages to state- owned dikes, water control structures, parking facilities, fences, signs and gates were estimated at over $ 30 million. Similar damage occurred on the federal Bear River Migratory Bird Refuge ( BRMBR). During the floods, production of ducks and geese dropped by 80 percent and fall swan use decreased over 90 percent. Total bird use in marshes decreased nearly 90 percent and public use all but disappeared. As the water depth increases, thousands of acres of brackish and freshwater marshes, as well as upland habitats, are flooded. This forces birds, particularly nesting species, to move to higher ground. In many areas around the lake, the upland buffer is no longer available because of human development. Either natural or anthropogenic flooding events could result in large population reductions of breeding birds, though there would again be some differences between long- term local events and short- term broad- scale events. Although potentially damaging to structures in WMAs, fluctuations in lake 32 |