Agenda - Council - 12/12/1995 - Laserfiche WebLink

Home

Sunwood Drive Miti~ati. on (2-114P) November 21, 1995 The elevation of the proposed ditch blocks/dike must primarily be based on the existing pole building near Section 3. Additionally, it appears that the wetland extends to approximately the 862 contour on the orthophoto map. If we subtract the 1.5 foot bounce from 862 we get a ditch block elevation of 860.5. This also leaves a reasonable safety factor in regard to the pole building. The "natural" ground elevation in the vicinity of sections 2 and 3 is also roughly at elevation 860 to 860.5. If we fill in just the ditch to these elevations, we will have at least partially restored the wetland to its original conditions. But I still like the idea, at least at section 2, of building up the dike in the overbank area to slightly above the elevation of the block (to elevation 861). Higher flows will be confined to the ditch, making it easier to protect a short reach of the downstream channel with riprap. Channel protection is necessary since the Section 2 dike may not be submerged by high downstream water levels. A dike at Section 2 also provides a safeguard against the possibilky that there is a lower outlet outside of the channel itself. I see no need to build a dike in the overbank areas of Section 3 as it would not serve any purpose. But partially filling in the ditch at section 3 (to approximately elevation 860.5) should help further disperse flow throughout the wetland. I've highlighted this recommendation on the attached copy of the plotted cross sections. Again, does this recommendation seem reasonable based on your recent site visit(s)? Fortunately, if a dike/ditch blocks are built and for whatever reason don't seem to be working, or maybe working too well, they should be relatively easy to modify. I raised two issues during our conversation. The first dealt with the status of the public ditch, for which you indicated that the city would have to petition Anoka County to do any work in the public ditch. The city will also have to deal w/th the issue of flowage easements. I understand there is not any opposition to this proposal. The above recommendation is conservative, so we likely are having minimal impact of water levels at, or above the OHW. Please call if you have any questions. cc: Dave Ford I I I I I I I I I I I I I i I I I I