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• REGIONAL SURFACE WATER CHARACTERISTICS <br />The New Horizon 1 and New Horizon 2 mining areas are drained by Tuttle and Calamity Draws, <br />respectively. Both draws are perennial tributaries of the San Miguel River which in turn flows into <br />the Dolores River and finally to the Colorado River. These river systems are explained thoroughly <br />in lorns' et al. (1965) USGS Professional Paper, Water Resources of the UDOer Colorado River <br />Basin -Technical Report. In this report, these river drainages are placed in the Grand Division of <br />the Upper Colorado River Basin and in the subdivision between the Gunnison and Green Rivers. <br />Because of the gradual increase in the development of water resources within the Grand Division <br />in this century, streamflow records used for this report (1914-1957) were adjusted to reflect the <br />level of water-use developments (diversions, dams, irrigation, etc.) that existed in 1957. Although <br />the 1957 levels of development varied from basin to basin, the adjustments made in the reported <br />streamflow records were useful for comparing stream characteristics among the different basins <br />while accounting for the changes in streamflow and water quality caused by the increased <br />developments. Since little additional activity (diversions, dams, etc.) has occurred within the San <br />Miguel River basin since 1957, the information presented in lorns' et a1. (1965) report is considered <br />• to be representative of present conditions. <br />Regional Surface Water Flow. The precipitation that falls on the basins within the Upper Grand <br />Division of the Colorado is generated from large air masses originating from the Pacific Ocean and <br />the Gulf of Mexico. These air masses originating from these sources are pushed high into the <br />atmosphere, losing much of their moisture prior to entering these basins. The Pacific air masses <br />dominate from October through April, and the Gulf of Mexico air masses dominate during late <br />spring and summer. The higher streamflows within the Grand Division largely resultfrom snowmelt <br />during late spring and early summer. By late July, most stream discharges recede to base flow. <br />Little contributions are made to stream discharges resulting from the infrequent summer <br />thunderstorms. <br />In the lower altitudes of the subdivision between the Gunnison and Green Rivers, little snow <br />accumulates during the winter months; therefore, most spring runoff events occur principally in the <br />head waters of the Dolores, San Miguel Rivers, and in the LaSal Mountains. On a more local <br />basis, short duration, high intensity thunderstorms that fall on undeveloped (natural) watersheds <br />• provide some of the summer runoff. In addition, return water from irrigation, and water from <br />REVISED JULY 2006 2.04.7-25 <br />