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Jefrrey W. Schwarz Massey, Semenoff, Schwarz, and Bailey Mobile Premix Concrete, Inc. October 10. 2001 Page 7 Analysis of the Passage of the Flood Waters Photographic evidence indicates that prior to 1990 a levee, a Swale and the historic 1973 Slough were proximate to the relocated Bull Seep Drain Ditch. The MPC reclamation plan does not address the filling or removal of any of these pre-existing structures, but only the construction of anew structure i.e. the permitted relocation of the Bull Seep Drain Ditch. Historic evidence from the 1973 flood event has already identified a preferred path for flood waters: down the Bull Seep Slough. Overtopping and breaching waters in 1973 established this flood flow channel. This event predated the acquisition of this property by MPC, as well as their mining and reclamation operations on the property. At the time of the 200] flood event, the historic slough was separated from the main flow of the South Platte River by a "non-engineered" fill. The record shows that the area of concern on May 5'" had actually breached five (5) months prior. This fill area further breached due to natural progressive hydraulic processes. Had the MPC reclamation plan been in place at the time of the failure, the remnant levee, Swale and historic 1973 channel would have directed any and all out of channel flows towards the historic Bull Seep Slough. [n this manner, flood waters would have followed the identical course as they actually did in the May 5, 2001 stream capture. MPC's failure to follow their approved reclamation plan is inconsequential relative to the behavior of the stream on that day. This action was not the cause of the downstream damage to the hydrologic balance. Finally, channel hydraulic analysis and survey data indicate that both the existing Bull Seep Drain Ditch and the "designed and permitted" Bull Seep Drain Ditch aze undersized to pass the estimated overbank flow of May 5, 2001 (approximately 2000 cfs). As a consequence, the majority of flood flows which left the South Platte River were conveyed towazds the Bull Seep Slough as sheet flow. Under sheet flow conditions, flow velocities are low and non-erosive (reference over bank velocities of approximately 2 fps in the HEC-2 backwater model utilized by Gingery Associates, Inc., Flood Hazard Area Delineation, 1977). Once sheet flow reached the Bul] Seep Slough it converged into concentrated channel flow and velocities increased. The erosive energy of this concentrated flow resulted in the observed changes to channel geometry. Conclusions In summary, my firm and I have reviewed the Howe Pit site and performed a qualitative geomorphic and quanititative hydraulic analysis of the bank failure of May 5, 2001. Based on our forensic analysis, we conclude that this bank failure was the result of numerous factors developing over the 28 years preceding the actual bank failure in question, and that were in clear evidence months prior to May 5, 2001. The present location of the Bull Seep Drain Ditch was not a factor in the failure mechanism, however factors operating in the failure mechanism include: 1. The Branmer Diversion Structure was constructed in 1947 and since its construction has served as a grade control. As such the structure prevented significant vertical adjustment of the South Platte River in the immediate upstream reach.