ENFORCE26865 - Laserfiche WebLink

Home Browse Search

etfiey W. Schwarz Mazsey, $emenoR, Schwarz, and Bailey Mobile Premix Concrete, [nc. October 10, 2001 Pagc 8 2. The 1973 flood event breached the right (east) channel bank and opened up a major new channel at the location of the Bull Seep Drain Ditch. This new channel became the Bull Seep Slough and was subjected to annual backwater from the South Platte River. Sometime after the passage of the 1973 flood event the Brantner Ditch Company repaired the breached river bank. The repair work was not completed using standard acceptable engineering design or construction practices. The breach was repaired by placement of silts and off site derived materials. The river-side of the repair work was protected by broken slabs of concrete. Again this method of bank protection does not meet standard acceptable engineering practice. 4. In the late 1970's and early 1980's in channel mining took place at a location, upstream from the repaired breach. The effect of this mining was to "rob" the normal river flows of their natural bed material sediment Toad and to create a "hungry" water situation. Increased bank erosion and increased tendency to meander resulted from this hungry water. Over the subsequent 20 years the angle of channel flow became progressively more acute to the 1972 repaired bank. Hydraulic conditions became progressively more severe such that the mode of attack and ultimate failure of the 1973 repair area on May 5'" was slow, progressive and originated from the river side, not the Bull Seep side. The May 5, 2001 flood event represented the culmination of these progressive attacks and resulted in the final failure of the non engineered 1973 fill. The present location and configuration of the Bull Seep were not factors in the capture of main channel flows and the ultimate damage associated with the May 5`h event. 6. Photographic evidence dated January I8, 2001 indicate that a breach of the bank in question existed prior to the May 5`" event. The effect of this earlier breach may have accelerated or may have been the catalyst of the bank failure of that day. 7. Hydraulic analysis and historical data support these conclusions. I hope the above assists you in your understanding of the reasons for this bank failure. If you have any further questions, please don't hesitate to call. Sincerely, LIDSTONE AND ASSOCIATES, INC. ~' ,lp. ~~- - pJ9 Christopher D. Lidstone, CPG President CDL:jab