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Cresson Pro'ect H dro ' eochemist AdrianBrown <br />day (i.e. storm water). Runoff occurs with an approximate 24 hour delay', and is approximately <br />given by the regression equation: <br />Flow (gpm) = 156 * [Precipitation (in/prior day)] - 41.3 <br />Volume (acre ft) = 0.69 * [Precipitation (in/prior day)] — 0.183 <br />4. During the entire year, there were a total of 9.6 acre feet of runoff at GV -03, representing the <br />equivalent of 0.10 inches of precipitation over the GV -03 catchment area of 1,124 acres. This <br />0.10 inches of the 14.97 inches of precipitation measured in Grassy Valley in 2010 represents a <br />basinal yield of 0.69 %. This is a very small basin yield; normal montane yields are in the order <br />of 25 -40 %. <br />In summary, there is almost no surface water flow in the valleys and gulches that exist over the <br />Diatreme. Most surface water infiltrates to the basin soil and bedrock before forming streams, and none <br />re- emerges from the ground as springs within the footprint of the Diatreme. <br />2.4 Ground Water <br />2.4.1 Ground Water Flow <br />Ground water flow from the District has been measured because essentially all infiltrating water has <br />been collected and removed from the Diatreme since 1903 by three principal historic drainage tunnels <br />(Plate 4): <br />1. Moffat Tunnel The Moffat Tunnel was driven in 1903 from a portal elevation of 8,800 feet from <br />the south of the city of Cripple Creek to the north -east, and is approximately one mile long <br />(Lindgren and Ransome, 1906). Flow from the tunnel was initially as much as 11,000 gpm, <br />reducing to less than 2,000 gpm by 1906. Flow from the tunnel ceased when tunnels at lower <br />elevations reduced the water level in the Diatreme below the elevation of the tunnel. <br />2. Roosevelt Tunnel The Roosevelt Tunnel was driven between 1910 and 1917 from a portal <br />located southwest of the city of Cripple Creek, at an elevation of 8,100 feet (Sheldon, 1915). The <br />tunnel was ultimately driven 4.6 miles, reaching into the heart of the District. Flow from the <br />portal rose to nearly 9,000 gpm by 1917, dropping back by the end of that year to about 4,000 <br />gpm (Henderson, 1926). Flow from this tunnel largely ceased when the Carlton Tunnel was <br />installed at a lower elevation. <br />3. Carlton Tunnel The Carlton Tunnel was driven in 1939 -1942 from a portal elevation of 6,890 <br />feet, with the portal located immediately downstream of the confluence of Cripple Creek with <br />Fourmile Creek (Vivian, 1940). The tunnel was ultimately driven approximately 6 miles and <br />enters the southern portion of the Diatreme. Flow from the tunnel was estimated to be 125,000 <br />gpm after breakthrough into the Portland No. 2 Shaft, but reduced rapidly to its then - normal flow <br />' This is based on the internal clock time for the Grassy Valley fluviometer and the GV -03 Parshall flume transducer. Storms measured at <br />the Grassy Weather Station are typically a day earlier than those measured at the Rigi Weather Station. The reported 24 hour delay may <br />be due to differences in clock times rather than hydraulics. <br />1385L.20120125 5 <br />