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<br />Reach No. 3 (Plate 7) <br /> <br />The New Mercer Canal carries the runoff from the upper portions of McClel- <br />lands Basin to Mail Creek. During periods of high rUllOff, the depth of f10w in the <br />canal becomes greater than orjginally designed for. This results in the inundation <br />of the ditch service road on the east and some associated erosion damage. At the <br />confluence with Mail Creek, excessive discharge velocities could cause some additional <br />erosionand/ordepositionofsiJt. Fina1Jy,overtoppingofthelarkboroughSubdi_ <br />vision detention pond along its east bank will also contribute to the flooding and <br />erosion problem in this reach. <br />ReaCh NO.4 (Plates 8 and g) <br /> <br />There is a substantial amount of overland flow through the streets and yards <br />in larkborough Subdivision during the lDO-year storm. Although the flows are not <br />above the first floor elevation for any of these units, there is the potential to <br />have structure and content damage to seventeen (17) homes. Between larkborough and <br />Shields Street, the floodplain consumes a considerable amount of ground whiCh is <br />presently in agricultural use. During floods here. there exists the pot€ntial for <br />crop and/or flood damage. <br /> <br />Reach No. 5 (Plate 9) <br /> <br />The Shi€lds Street crossing consists of one 15-inch corrugated metal pipe. <br />As a result, Shields Street is overtopped during euen minor storm events causing <br />traffic interruption and some erosion problems. Upstream of Shields Street, con. <br />siderableagricuJturalgroundisconsumedbyfloodplain. Finally,duringflooding, <br />the Pleasant Valley and Lake Canal would probably breach and thus require repairing <br />and probable removal of some silt deposits. <br /> <br />ReaCh No. 6 (Plates 10 through 13) <br /> <br />The lower portions of the McClellands drainageway have extremely wide flood. <br />plains as a result of backwater behind culverts at both Timberline Road and the Union <br />Pacific Railroad. Both of these crossings would be overtopped by 1O.year storms or <br />greater, and would be in danger of washing out. Because of the tall and steep em- <br />bankment of the railroad, extensive damage to the railroad as well as adjacent pro- <br />perty could result during a storm of 2s.year frequency or greater. <br />Upstream from Harmony Road, the McClellands drainageway has been improved as <br />part of the residential development which has taken place. and all improv€ll1€nts are <br />adequate for the IOD-year' design flows. 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