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Demonstration and Location of Permanent Drainageways <br />• As acknowledged by the Division, the nature of the semi-arid areas in <br />many parts of northwest Colorado produces an environment where rilling and <br />gullying are parts of the natural erosional processes in ephemeral <br />watersheds. Rule 4.14.6(2) allows for rills and gullies in excess of 9 <br />inches provided the permittee demonstrates that rilling and gullying is not <br />excessive and that the erosional patterns on the reclaimed site are <br />consistent with either baseline conditions or conditions of similar <br />undisturbed areas under good management practices. The Division therefore <br />requested that CYCC provide a demonstration evaluating the extent of rilling <br />and gullying in adjacent undisturbed areas accompanied with a discussion of <br />the environmental factors causing the rills and gullies, and the <br />relationship of the reclaimed land to similar undisturbed areas where rills <br />and gullies have formed. Colorado Yampa Coal Company complied with that <br />request in 1984 and 1985. A gully survey was conducted on undisturbed <br />areas immediately adjacent to the active Eckman Park mining operations. <br />This survey was conducted on areas of similar soil type, slope, topographic <br />• gradient, and vegetation as areas being mined in Eckman Park (See Map No, <br />16, Eckman Park Vegetation and Map 30, Eckman Park Soils). Five areas were <br />selected which exhibited evidence of active erosion ono gully formation. <br />The five sites selected for survey are shown on t•iap 28-1 (TR 87-14-1), <br />Undisturbed Area Gully Sampling Sites. At each site, a cross-sectional <br />profile was evaluated Dosed upon site specific evidence of erosion. An <br />imaginary plane was drawn to determine the exact extent of downcutting. <br />The lane was drawn to connect the two natural slopes bordering the gully. <br />The resulting area was considered as the current gully cross-section. <br />Figure 28-1, Undisturbed Area Gully Cross-Sections, depicts the <br />cross-sectional profiles generated from the five sites. pleasured depths of <br />down cutting ranged from 9.5 to 20.3 feet. The watersheds above the gully <br />sites are equal to or smaller than watersheds within the Eckman Park Mine. <br />Colorado Yampa Coal Company also compared the densities of gullies on <br />undisturbed land to the density of proposed permanent drainageways in the <br />reclamation. An area possessing similar soils, slopes, and vegetation as <br />. the mined area was selected for this analysis. Gullies found within the 400 <br />c8-7 <br />