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will be an ongoing project throughout the field season in conjunction with <br />the rill and gully survey. It is understood the remedial work will be <br />• completed by the end of the field season, which is typically October 31. <br />The Division may review ongoing survey, monitoring, and repair work <br />during the field season at their convenience. <br />Guidelines for Contour Furrow Construction <br />The frequency and depth of contour furrows and the frequency of check <br />bridges in individual furrows is determined primarily by: <br />1. Magnitude of runoff from design precipitation event. <br />2. Topographic slope. <br />3. Drainage area above the region to be contour furrowed. <br />The principle of contour furrowing is to increase depression storage to <br />the extent that the runoff from the drainage area may be completely <br />contained. Eventually, vegetation will become established and the contour <br />• furrows will become less prominent. As vegetative growth increases and thus <br />provides greater soil stability, the importance of contour furrows for the <br />control of erosion and sheet flow will decrease. <br />The design event used for this guideline is the 10-year, 24-hour <br />precipitation event. According to the National Weather Service publication <br />"NOAA" Atlas 2, "Precipitation - frequency Atlas of the Western United <br />States", the precipitation from a regional 10-year 24-hour event is 1.8 <br />inches. As the runoff from this event would probably exceed most snowmelt <br />runoff events in the area, it is an appropriate design criteria. Runoff <br />volumes from the design event were estimated using the techniques outlined <br />in "Procedures for Determining Peak Flows in Colorado: (SCS, 1977). For <br />this analysis, standard antecedent moisture conditions were assumed; thus, <br />not all the precipitation falling on the reclaimed area contributes to <br />runoff. A curve number of 82 was used in the calculations which is <br />applicable for disturbed areas. As the slope of the reclaimed surface does <br />• <br />24-6 <br />