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17 <br />4 SURFACE WATER <br />4.1 Regional conditions <br />The proposed Collom Mine is located in the Yampa River watershed, which drains the <br />upland areas that comprise the Danforth Hills. Individual watersheds within the project <br />area include Straight Gulch, Collom Gulch, Little Collom Gulch, and Jubb Creek. The <br />regional drainage pattern in the Collom study area is shown on Figure 4.1. The East <br />and West forks of Jubb Creek merge northeast of the site. Jubb Creek flows into Wilson <br />Creek, which flows into Milk Creek and then into the Yampa River. The remaining <br />drainages are tributaries of Morgan Gulch, which joins the Yampa River approximately <br />10 miles north of the site. The Yampa River flows west through the Axial Basin and <br />drains much of the northeastern plateau region of northwestern Colorado. <br />The topography of the Collom site is influenced by the asymmetric Collom Syncline. The <br />southern limb of the syncline dips gently to the northwest and northeast, and surface <br />water features are sub parallel to dip. North of the proposed Collom Mine, the streams <br />cut through the steeply dipping beds of the north limb of the syncline. The structure of <br />the syncline exerts a major control on groundwater flow, surface water flow and aqueous <br />geochemistry. Since the streams effectively pass into a different hydrologic and <br />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 <br />of the upper Williams Fork Formation. In the upland areas of the Collom study area, the <br />stream valleys are typically narrow (100 to 200 ft wide) and steep -sided with gradients of <br />approximately 0.03 to 0.05. The stream channels are typically 10 to 20 ft in width and <br />incised about 5 to 10 ft into valley fill. The valley fill is composed of sand, clay, silt and <br />some gravel (Reheis, 1981). The vertical heterogeneity of the valley fill indicates that <br />sediment transport is episodic and highly dependent on flow. <br />Many reaches of the incised channels have unstable cut banks and recently - slumped <br />surfaces. The sides and bottoms of the stream channels are vegetated with a mixture of <br />sage, cottonwood, and box elder. There is little sinuosity developed in the channels. <br />Closer to the axis of the syncline, the stream valleys are wider with moderate side <br />slopes. On the north limb of the syncline, Morgan and Collom Gulches and Jubb Creek <br />have eroded through the steeply south - dipping rocks of the Williams Fork and Iles <br />Formations and into the top of the Mancos Shale. Stream gradients in this area are <br />approximately 0.02. <br />2572 -R2 <br />Colowyo Coal Company <br />Water Management Consultants <br />