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Environmental Scientists and Engineers, L.LC <br />JBR, 1998 Study <br />The JBR report does not attempt to determine if lands meet the CCDMG definition of an <br />AVF. It does, however, provide data and observations that may be useful to support the <br />evaluation of lands with respect to AVF determination. <br />3.5.3 Floodplains <br />Floodplains within the proposed lease area are essentially non - existent because perennial <br />streams are not present. <br />3.6 Hydrology Resources <br />3.6.1 Surface Water <br />Regional Conditions <br />The proposed lease area is located in the Yampa River watershed, which drains the <br />upland areas that comprise the Danforth Hills (WMC 2005). Individual watersheds within <br />the project area include Straight Gulch, C611om Gulch, Little Collom Gulch, and Jubb <br />Creek. The regional drainage pattern in the Collom study area is shown on Figure 7. The <br />East and West forks of Jubb Creek merge northeast of the site. Jubb Creek flows into <br />Wilson Creek, which flows into Milk Creek and then into the Yampa River. The <br />remaining drainages are tributaries of Morgan Gulch, which joins the Yampa River <br />approximately 10 miles north of the site. The Yampa River flows west through the Axial <br />Basin and drains much of the northeastern plateau region of northwestern Colorado. <br />The topography of the proposed lease area is influenced by the asymmetric Collom <br />Syncline. The southern limb of the syncline dips gently to the northwest and northeast, <br />and surface water features are sub parallel to dip. North of the proposed Collom Mine, <br />the streams cut through the steeply dipping beds of the north limb of the syncline. The <br />structure of the syncline exerts a major control on groundwater flow, surface water flow <br />and aqueous geochemistry. Since the streams effectively pass into a different hydrologic <br />and hydrogeologic regime when they flow north of the syncline, the surface water study <br />focused on conditions within the syncline. <br />The surface drainage system consists of narrow valleys cut into the relatively soft units of <br />the upper Williams Fork Formation. In the upland areas of the proposed lease area, the <br />stream valleys are typically narrow (100 to 200 feet wide) and steep -sided with gradients <br />of approximately 0.03 percent to 0.05 percent. The stream channels are typically 10 to 20 <br />feet in width and incised about 5 to 10 feet into valley fill. The valley fill is composed of <br />sand, clay, silt and some gravel (Reheis 1981). The vertical heterogeneity of the valley <br />fill indicates that sediment transport is episodic and highly dependent on flow. <br />P PROJECTS C'alnrry.?,I SW EA Final nl..I- v- F.: \ 0(3,10 <br />25 <br />