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1 <br /> APR 07 197 14:01 MATTKE ENGINEERING, INC. 6127830300 T0: P03 <br /> would have to get about 18 inches deep before it would overflow <br /> onto the County road. This culvert had the capacity to handle <br /> approximately 5 cfe without overflowing. Thus, without the homes <br /> on the hill, the original culvert was able to handle a 4.0 inch <br /> rainfall. In fact, the original culvert had the capacity to <br /> handle up to approximately a too-year rainfall event (5• <br /> inches/24 hours) , which would have produced a 5 cfs (approx.) <br /> discharge at the culvert, before construction of the homes on the <br /> hill. <br /> construction of the homes on Tonkaview increased the drainage <br /> area (of the original culvert) to approximately 3.55 acres, and <br /> increased the runoff curve number to 75 for the culvert <br /> watershed= Recent changes by the County and City (the County <br /> added curbing, and the City added a 611 pVC pipe draining to the <br /> west from the northwest corner of the intersection of Tonkaview <br /> and CR 19) have reduced the drainage area to approximately 3.39 <br /> acres. Even after these recent reductions in drainage area by <br /> the County and City, the peak discharge at the culvert remains <br /> approximately 6 cfs iii a 4.o inch rainfall <br /> Recent changes to the County Road 19 drainage included lowering <br /> the culvert, increasing its capacity toapproximately 6 cfs (the <br /> same discharge as was produced by the 4.o inch storm) , and <br /> placing curbing along the edge of the pavement. statistically, <br /> .we can expect a 4.2 inch storm to hit this area every_ 10 years, <br /> on the average. Consequently, we can expect that, if no changes <br /> are made to the current drainage system, the existing culvert <br /> will have insufficient capacity about: every 10 years or GO. <br /> Placing the curbing included plaoiRg a raised (about 1-1/2 inch) <br /> lip of bituminous pavement in front of your driveways. In <br /> additiob, the pavement was graded to pitch away from the Bessesen <br /> driveway, so flows oomin down the curb line will now gross the <br /> County road without rUnn�ng into the 8e4sasen driveway. 'Thus it <br /> appears that the Beason-an house is now protected from CR 19 water <br /> ru-n i ng down the driveway. <br /> Oft the other hand, placing the curbing along the County road has <br /> increased the potential for damage from CR 19 water to the <br /> dawicki. home. As the curb is higher than the ditch bank, culvert <br /> overflows can nolonger escape down the County road pavement, but <br /> instead will overtop the dutch bank +end erode a path directly <br /> toward the SaVIOU home. It will only take a few minutes of <br /> erosion before the entire ditch floe will be running around and <br /> through the Sawicki house. It is expected that the damage to the <br /> Sawicki home could far faxoeed that suffered in 1995 if the <br /> culvert capacity is exceeded under present conditions. <br /> With the potential for damage to homes, it is ordinary <br /> engineering practice to provide protection for at .least the loo- <br /> year event, 5.9 inches/24 hours. With the homes on the hill, <br /> such an event would be expected to produce a discharge at the <br /> culvert of about 11 cfs, even after the recent changes by the <br />