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• 3.7 Results <br />Vegetation response, decreased flow rates and reduced gully formation were the primary factors in assessing <br />the success of drainage reconstruction projects at Trapper Mine. <br />Postmine herbaceous canopy cover, herbaceous production, and woody stem density were evaluated in <br />recons[ruted drainage areas in 1988, 1989, 1990, 1991, and 1992 and compared to sample data from undis- <br />turbed premise drainage areas. (Sampling was conducted on drainageways reconstructed in 1987.) Various <br />pos[mine drainage treatments were incorporated to evaluate vegetation response on topsoiled, non-top- <br />soiled, irrigated, and son-irrigated drainage segments (Table 1). Treatments on undisturbed areas were irri- <br />gated and non-irrigated drainage segments (Table 1). Generally, vegetation measurements were lower in <br />reconstructed drainageways than in undisturbed drainage sites in the initial growing season. However, by <br />the end of the thud growing season vegetation parameters on reclaimed drainage areas were equal to or <br />exceeded those measured on undisturbed drainage areas. A list of plant species encountered in reclaimed <br />drainages and in undisturbed drainages is provided in Tables 2 and 3 respectively. <br />Vegetation response was the best on topsoiled and irrigated treatments and was significantly higher when <br />comparing topsoiled versus non-topsoiled areas without irrigation. The overall herbaceous canopy cover for <br />all reconstructed drainage veatments in 1988 (measure of initial growing season) was 39% compared to <br />71% on undisturbed drainage segments. In 1989, herbaceous canopy covet had increased to 60% in recon- <br />structed drainages and decreased on undisturbed drainage segments to 69% cover. Herbaceous canopy <br />cover within postmine drainageways and in undisturbed drainages was equal at 65% in 1990. In 1991, <br />herbaceous canopy cover measured 71% within undisturbed drainages and 66% in reclaimed drainages. <br />Percentages in 1992 were 89% and 80%, respectivety. <br />• Herbaceous primary production averaged 876 IbsJose in reconstructed drainages and 1943 Ibs/acre on <br />undisturbed sites fn 1988. In 1989, herbaceous primary production decreased to 420 lbs/acre on recon- <br />structed drainages and 521 !bs/acre on undisturbed drainage segments. The reduction in production is 1989 <br />compared to 1988 was a result of severe drought conditions in the area during 1989. Herbaceous primary <br />production averaged 1712 pounds/acre in postmine drainages and 1629 pounds/acre in undisturbed <br />drainages in 1990. In 1991, herbaceous production was 1,802 pounds/acre in undisturbed drainages and <br />2,545 pounds/acre in reclaimed channels. Production in 1992 was 2,000 pounds/acre and 1,865 pounds/acre, <br />respectively, <br />Woody stem densities on undisturbed drainage areas averaged 4888 stems/acre for all three years compared <br />to 471 stems/acre in 1988, 897 stemsJane in 1989, and 1,304 stems/acre is 1990 and 1,945 stems/acre <br />(stems/acre are planted densities, not actual survival) on reconswaed drainage areas. <br />Flow rates have been signifipntly reduced following the installation of stock tanks and dozer basins on <br />reclaim and spoil areas, respectively. Discharge readings were recorded from a 10-year, 24-hour parshall <br />flume (with Stevens Water Level Recorder) located in the north end of the Coyote Gulch reconstructed <br />drainage channel The peak flow in 1987 (22.24 cfs) occurred as a result of a high intensity thunderstorm in <br />June (.74" ppt) and posed severe erosion within the newly regraded drainage channel In 1988, following <br />drainage reconstruction and water retention sVategies, the peak flaw rate associated with a .53" precipita- <br />tion event (June) reeistered .04 cfs of discharge water. Similarly, a high intensity thunderstorm in July 1989 <br />(.75" ppt) resulted in a discharge of 1.73 cfs. The peak flow in 1990 and 1991 was 1.78 cfs and 1.38 cts <br />respectively and occurred during March. During 1992 there was no recordable discharge. In addition to <br />assisting in runoff control, the proper frequenry and distn'bution of livestock ponds has aided in evenly <br />spreading big game animal and livestock use over the entire reclaimed area, thus reducing their impact on <br />• vegetation establishment <br />