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TABLE III-2 area has been historically tributary to Coal Creek and not to Upper Big Dry Creek. The portion of the Upper Big Dry Creek basin that lies within the study area (headwaters to Indiana Street) contains approximately 2995 acres. Only 480 acres of the basin lie within the Rocky Flats Plant site Buffer Zone. WALNUT CREEK AT INDIANA STREET AGGREGATE BASIN CHARACTERISTICS(l) Area 3.71 sq mi Basin length 5.7mi La 2.21 mi Basin slope 0.027 ft/ft Impervious existing 14 percent Pervious retention 0.49 in Impervious retention 0.10 in InfUtration, initial 3.75 in/hr Inflltration, fmal 0.55 in/hr The basin is similar to the Woman Creek and Walnut Creek basins with gently sloping uplands followed by steep gullies draining to Upper Big Dry Creek, and then broader valleys finally discharging to Standley Lake. The Spring Creek area of the basin contains steep foothills draining to a channel with up to an 8 percent slope. The aggregate basin characteristics of the Upper Big Dry Creek drainage basin are listed in Table III-4. Ponds (I) Drainage basin parameters are defined in this section ("Rainfall/Runoff' subsection). A description of the determination of the parameters for specific basins is contained in Section IV ("Description of Models" subsection). There are fourteen reservoirs (called "ponds") located in the Rocky Flats Plant Buffer Zone. Eleven of these ponds are used for effluent, stormwater runoff and stream baseflow detention. Three are presently not used for water management. TABLE III.3 Characteristics of each of the Rocky Flats ponds are presented in Table 111-5. The ponds are interconnected through a series of pipes, valves, and pumps used for the management of water and potential contaminants. A schematic diagram of the ponds is presented in Figure III-3. For hydrologic modelling, the ponds were analyzed using a modelling assumption that the ponds were full at the start of the storm and flows were not attenuated through them. The storm events that would cause an uncontrolled spill over the diversion dams above Pond A-I and Pond B-1 into the lower ponds were identified in Section IX. The capability of the terminal ponds to store the lOO-year runoff volumes is analyzed in Section IX. WOMAN CREEK AT INDIANA STREET AGGREGATE BASIN CHARACTERISTICS(l) Area 4.51 sq mi Basin length 5.68 mi La 2.27mi Basin slope 0.028 ft/ft Impervious existing 2 percent Pervious retention 0.52 in Impervious retention 0.10 in Inftltration, initial 3.64 in/hr InfUtration, fmal 0.55 in/hr The Landfill Pond is an off-stream reservoir located north of the Core Area immediately east of an operating landfill. The reservoir collects runoff and landfill leachate from a approximately 38-acre drainage basin tributary to the landfill. (1) Drainage basin parameters are defmed in Section III ("Rainfall/Runoff Parameters" subsection). A description of the determination of the parameters for specific basins is contained in Section IV ("Description of Models" subsection).