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)eihey W. Schwarz Massey, Semeno(f, Schwaa, and Bailey Mobile Premix Concrete, toe. October 10, 2001 Page 2 field survey of several cross sections within the channel teach of interest; hydrologic flood frequency analysis of the peakflows of record; and hydraulic analysis of the May 5th event. Summary of the Bank Failure Reportedly the right or east bank of the South Platte River failed sometime during the aflemoon and evening of May 5, 2001. The flood event commenced during the evening of May 4'h and achieved a peak flow of approximately 6000 cfs at approximately 7:OOPM on the evening of May 5'". Upon failure of the bank, a certain amount of the main channel river flow was diverted into the Bull Seep Slough and resulted in erosion and sedimentation within that slough. My firm estimates that approximately 2000 cfs may have traversed the Bull Seep Slough at some time during this flood event. The net result was the Bull Seep Slough was widened and deepened by the captured South Platte River waters. It should be further noted that evidence of a failure at the area in question was evident some five (5) months before the May 5`" event. The existing breach in the area of concern provided added opportunity for the river to pass flows into the Bull Seep Slough. Based on the reported information provided by the adjacent property owner (Ken McIntosh) and supported by historical aerial photograph analysis, this same stream bank had failed during a previous May, 1973 flood event and flood waters were captured by the original Bull Seep Drain. The 1973 flood event enlarged, widened and deepened the drain ditch, which ultimately created the Bull Seep Slough. Following the passage of the 1973 flood event, the Brantner Ditch Company repaired the breach. Mr. McIntosh described the material used in the repair as silt and unconsolidated fill, which was removed from his property. Photographs taken of the failed levee support this statement. Furthermore, large flat slabs of concrete rubble were used as erosion protection on the river-side of the repaired stream bank. Visual evidence of this repair work is present onsite. There is no evidence or reported information that the above described bank repairs were "engineered". There is photographic evidence that the "repaired bank" was breached subsequent to the 1973 event and prior to the May 5, 2001 flood even[. Photographs taken on January 18, 2001 indicate that an erosion cut may have partially opened the embankment. Evidence of an opening was also noted in the October 10, 2000 aerial photo. There is no evidence that this erosion cut was repaired prior to the May 5`h flood event. Professional Qualifications I am President of the professional consulting firm Lidstone and Associates inc. and a professional geologist with over 20 years experience in river mechanics, hydraulics, geomorphology and sediment transport. I am familiar with the Mobile Premix Howe Pit site and have reviewed the hydrologic conditions associated with the bank failure. I have completed similar studies for existing and proposed public works, private developments and mining related projects in 36 states, as well as several foreign countries. I have addressed gravel mining projects and prepared mine and reclamation plans for the gravel industry in the States of Colorado, Wyoming, Oregon, Montana, Hawaii, Minnesota, Washington and California. Since 1986, my firm has completed surface and ground water smdies, river restoration, engineering construction and environmental