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• area slopes generally to the west at about 130 feet/mile. The lower reaches of Tuttle Draw are steeper. Topographic relief at the mouth of Tuttle Draw is about 300 feet. The Tuttle Draw drainage area encompasses elevations from 6580 feet to 5240 feet with an average gradient of about 140 feet/mile. The stretch of Tuttle Draw that drains to the revised New Horizon 2 mine permit area has a gradient of about 98 feet/mile. Channel Characteristics The perennial nature of flow occurrence in both Tuttle Draw and Calamity Draw in the vicinity of mining is largely due to irrigation. Surface water (irrigation return water) and to a lesser extent, ground water (originating from the upland, irrigated fields) discharging into Calamity Draw has resulted in deeply incised, narrow main channels that have relatively stable bank sides. Vegetation encroachment over time near and on the channel banks has enabled the channel to stabilize the incised channel geometry and stream course. In contrast, Tuttle Draw is developed on resistant bedrock. • The deeply incised but yet stable characteristics of the main channel(s) in Calamity and to a lesser extent Tuttle Draw can be attributed to the increased influence by man's activities. In a typical semi-arid environment, (f 5 inches annual precipitation) channel geometries and courses generally reflect the infrequent and highly variable discharges and sediment loads resulting from intense summer thunderstorms. These semi-arid ephemeral channels often feature shallow and wide bottoms with unstable banksides. Ephemeral channels will adjust geometries and courses to accommodate the varying discharges and high sediment loads, often radically changing local reach geometries and courses during large, flash flood events. However, as more upland areas are transformed from natural, semi-arid vegetation to pasture, hayland and cropland by irrigation, streamflow variability (discharge and sediment loads) becomes dampened and is controlled by the increased vegetation and manipulation of the drainage system. This results in channels becoming more stable and often more incised, due to lower, less variable flows with lesser sediment loads. This occurrence is reflected in both the main channels of Calamity Draw and Tuttle Draw. Gradients of certain reaches within the stream channel varies. For instance, the overall stream gradient of Calamity Draw is .0248 ft/ft while the segment of the reach of Calamity Draw nearest • the New Horizon 2 mining area (SW-N101 to SW-N107) is .0083 ft/ft. Gradients calculated for the REVISED JULY 2006 ~ 2.()4.7-29