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<br />. ICON has performed a cursory analysis of the watershed characteristics and drainage areas <br />from the various tributaries in the basin (see attachment B), This work will be expanded on <br />in the final phase of the study, <br /> <br />. The CWCB presented results of the flood hydrology analysis as well as the 'peak discharges <br />from the 1999 and 1997 flood events for comparison purposes, Flood frequency data for the <br />Elk River near Milner are: 100-year flow = 6,200 cfs; 50-year flow = 5,900 cfs; I a-year flow <br />= 5,200 cfs. The June 3, 1997 peak flood flow was 5,740 cfs (approximately a 25-year <br />event), The 1999 peak flood flow was approximately 4,430 cfs (less than a 10-year flow), <br /> <br />. ICON presented technical information on stream geomorphology to help identify the <br />problems and needs along the lower reach of the Elk River, Stream stability is a function of <br />channel slope, bed and bank material, dominant discharges, flood discharges, man-made <br />features, and other factors. (See Attachment C for stream and flood profiles), <br /> <br />. The large meander (bend) in the Elk River approximately 1,000 feet upstream of the highway <br />40 bridge is at risk for further erosion and migration. Complete failure of the embankment <br />and levee system along the outside of the bend would be catastrophic for homes, state <br />highway 40 and the bridge, the county road, and the railroad line. <br /> <br />· Maximum stream velocities for the 100-year flood along the outside of the large meander <br />(bend) are on the order of 12 feet/second. This high velocity presents challenges for <br />stabilizing and mitigating the streambank to prevent a major disaster. (See attachments D and <br />E). <br /> <br />· ICON presented various alternatives for protecting the streambank in the most critical areas <br />in lower 0.9-mile reach of the river. Drawings and figures were displayed for the audience to <br />present the conceptual design features. The most feasible solution is to protect the bank with <br />riprap, in addition to providing a rock sill (grade control structure) at the upstream end of the <br />meander. <br /> <br />· Cost estimates for various stabilization alternatives were also presented. The range of costs <br />for the minimal approach up to the recommended alternative is $60,000 to $1,000,000, <br />respectively. (See Attachment F), <br /> <br />Public Concerns <br /> <br />The meeting audience generally feels comfortable with the engineering results and <br />recommendations. The estimated cost for improvements (i.e. mitigation measures) was much <br />higher than expected. The main concern of the interested parties was "what can be done, how <br />much will it cost, and how long will it take". The audience also recognized that there are two <br />hazards related to the Elk River: 1) Overbank flooding from flood events greater than about at <br />lO-year frequency, and 2)erosion and stream migration that could severely jeopardize public and <br />private lands and facilities. The main focus of the ICON study is the latter of the two, The <br />overbank flooding problem will not be solved as part of the current study. <br />2 <br />