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HomeMy WebLinkAboutKNIK HEIGHTS General Information ANCHORAGE, ALASKA 99502-0650 O~ (907) 786-8160 TONY KNOWLES, Anchorage DEPARTMENT OF PUBLIC WORKS (3580 East Tudor Road). July 22, 1986 R&M NO. 651049 Mr. Bruce Ericson State of Alaska Department of Environmental Conservation 437 "E" Street Anchorage, AK 99501 RE: Furrow Creek Drainage Basin and Knik Heights Subdivision Dear Mr. Ericson: Pursuant to our noon meeting conversation on June 26, 1986 regarding the Furrow Creek Drainage Basin and the drainage problems in Knik Heights Subdivision, I have prepared this letter stating our department's investigations and conclusions. During the past two years, the Municipal Department of Public Works has investigated drainage complaints within Knik Heights Subdivision. This subdivision is located within Section 27, T12N,R3W, in an area generally known as the "hillside" portion of the Municipality. Evidently, development uphill from Knik Heights Subdivision has concentrated seasonal surface runoff in the low topographic feature that traverses Knik Heights Subdivision. Concern has been expressed from the Municipal Department of Health and Human Services and from your staff that the low topographic feature is an active branch of Furrow Creek. Application of State and Municipal creek setback requirements would adversely affect approximately seventeen existing homes. Both Municipal and Private consulting engineers have investi- gated the drainage in Knik Heights Subdivision, and their results and conclusions are as follows: 1. The low topographic feature that traverses Knik Heights Subdivision is a seasonally active drainage channel that lies within the Furrow Creek Drainage Basin. 2. Test holes and soils maps indicate that the soils in this area are predominantly gravels with silt and sand'lenses. Mr. Bruce Ericson Page 2 July 22, 1986 o No water table was found to a depth of 15 feet in the test hole records of twelve properties adjacent to the drainage channel. No observable flow in .the channel was found prior to spring breakup. 5. Breakup conditions correspond to snowmelt runoff behavior. Water was found in the channel, and this water causes local drainage problems. No observable flow in the channel was found after breakup. During spring breakup conditions, a surface water connection of this channel to Furrow Creek was not found. The low groundwater table (below 15 feet) and gravelly soils do not support the contention that the drainage channel is a creek. Our conclusion is that the drainage feature through Knik Heights Subdivision is a seasonally active drainage channel that contains and transports surface runoff for only a few weeks each year during spring breakup and perhaps during an unusally large rainfall event. We did not find sufficient evidence to support classification of this drainage feature as a creek, and in fact, we found the hydrologic and hydraulic conditions of this drainage channel to be similar to a roadside drainage ditch. Unless you provide eviden~ce contrary to our findings, we will continue with our efforts to solve the drainage problems in Knik Heights Subdivision, without requiring the solution to address storm setbacks for on-site septic systems. If you have any questions, please call me at 786-8109. J. ~avid Norton, P.E. Municipal Engineer JDN:ed xc: Jewel Jones, Director, Health and Human Services Chip Dennerlein, Director, Intergovernmental Affairs R&M Consultants, Inc.