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• <br />In any case, the peak flow in the ditch, not the quantity of <br />rainfall, is the critical factor that needs to be considered <br />in determining whether the design flow capacity was exceeded. <br />This is addressed in item three below. <br />2. Colowyo points out that a DMG inspection report written <br />11 days prior to the storm indicates, "As a whole, ditch <br />performed well its first runoff season". <br />The reference to runoff season in the above statement refers <br />to the performance of the ditch in handling snowmelt during <br />the spring runoff season. The statement is not relevant to <br />runoff from thunderstorms. <br />3. Colowyo contends that the observed flows in the ditch <br />exceeded the design flows for a 10-year, 24-hour event. If <br />this is the case, there may be grounds for vacating all or <br />portions of the NOV. However, I do not feel that enough <br />documentation has been provided to make that determination at <br />this time. Following issuance of the NOV, Division staff <br />measured cross sections and high water marks in the ditch at <br />documented sites. Calculations are being made to determine <br />how large the flows were. Without similar evidence from the <br />operator, I do not believe it is appropriate to make a <br />determination on the size of flow. Even with sufficient <br />estimates, conslusions drawn from these types of calculations <br />are tenuous. <br />This topic has been given considerable thought and debate <br />during assessments of past NOV's at other sites. Because the <br />burden of proof is on the operator and because only minimal <br />data has been provided at this time, I would recommend the <br />operator make a better documented case at an assessment <br />conference. In my opinion, the case has not been made at this <br />time. <br />4. Colowyo points out that their calculations indicate the <br />lower Goodspring Creek monitoring site experienceed flows of <br />153 cfs during the storm, which is three to four time greater <br />than any flow observed during the past ten years of <br />monitoring. This fact, by itself, is not relevant to the NOV. <br />You should also be aware that this NOV was modified shortly after <br />Colowyo drafted their request for vacation. The NOV was modified <br />to include unstable sections of the ditch system which were not <br />cited in the original NOV and requires revised designs for those <br />portions of the ditch. <br />