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441" - <br /> AFR 07 197 14:00 MATTKE ENGINEERING, INC. 6127830-700 T0: P02 <br /> Mattke Engineering# Inc. <br /> 7671 Central Ave. N.E. Fridley, MN 55432 • (612)783-0300 �G <br /> April 7 , 1997 <br /> Z . Peter & Katheryn Sawicki Z <br /> 4510 North Shore Drive <br /> Orono, MN 55364 <br /> John & Beth Bessesen iL <br /> 4500 North Shore Drive <br /> Orono, MN 55364 <br /> re: Report on Drainage Analysis <br /> Dear Home owners: <br /> At your request, I have investigated the factors leading to <br /> failure of the culvert under the Sawicki driveway to carry the <br /> discharge from a 4.0 inch rainfall on August 6, 1995, which <br /> resulted in water damage to your properties. In summary, the <br /> cause of the problem was the construction of homes up the hill on <br /> Tonkaview, which increased the runoff rate in the County Road 19 <br /> ditch to the point that the culvert under the Sawicki driveway <br /> could not handle the increased discharges. The excess water then <br /> overflowed the ditch and ran down the edge of the County Road 19 <br /> pavement to the Sawicki driveway. There, the flaw apparently <br /> split, with about half continuing down the County road to the <br /> Bessesen driveway, and the other half running down along the <br /> Sawicki driveway. The overflow water apparently overtaxed the <br /> private drain systems of the two residences, resulting in flood <br /> damage to the homes. In addition, the flows eroded the bank <br /> beside the Sawicki driveway and around both houses, caused damage <br /> to the slopes, and deposition of eroded material in both yards. <br /> Before construction of the homes on Tonkaview, there was a <br /> drainage area contributing water to the culvert of approximately <br /> 2.6 acres. The dr-ainage area had approximately 0.4 acres of <br /> impervious surface) and the remaining area was wooded with <br /> grassed areas.' The sail type is a Kilkenny loam, described as a <br /> soil susceptable to erosion. Based upon these factors, a SCS <br /> curve number for runoff is estimated at CN-66 for the condition <br /> before the homes were constructed. When the SCS hydrology model <br /> is applied to the above conditions, a 4.0 inch rainfall would be <br /> expected to generate a peak discharge at the culvert of <br /> approximately 2 cYs. <br /> Based upon visual evidence, the original culvert under the <br /> Saw 1crni driveway wua s 15tI CHP, buried deep enough that the water <br /> = Resi dentia! &Corn;ncrcia:Deuc.opm.ent <br />