01-11-1988 - Agenda Packet City Council - regular meeting

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2.0 Prevention FL' are erosion problems can be prevented by controlling three factors: 1) rooftop drainage; 2) surface runoff from lawns and yards; and 3) seepage of ground water at the toes of steep slopes and at the base of retaining walls. Roofs should be guttered and the drainage directed, as much as possible, toward the street. Where grading permits, rooftop drainage from the rear of the house can be carried to the street in shallow subsurface drains. In special cases, drains can carry rooftop drainage down slope. Subsurface drains should be six-inch diameter corrugated polyethylene unperforated tubing. Surface runoff from lawns, yards, or unguttered portions of roofs must be controlled to minimize water volume and velocit , at any single point. Landscaping should be modified to prevent channelling of surface water. Low ii, is or berms can be constructed along the slope crest. Water ponded behind the walls must be drained through subsurface storm sewers. Eight -inch diametwr corrugated polyethylene unBerforated tubing can handle drainage from approximately 10,CC0 square feet if it slopes greater than 1 on 2 (50% grade). Inlets -rust be protected from trash, leaves, etc. Outlets must discharge onto riprap. Vents must be placed in the line where there are significant changes in grade. Many slope failures are caused by excessive pressure exerted by gret:nd water at the toes of s!opes. Subsurface drains i unning along the contour at the tees o, slopes and behind retaining walls will relieve the excess pressure and prevent slumping. Standards for subsurface drains are given above. 3.0 Seeding and Mulching It is importard ►o develop a good vegetative cover on steer) slopes as quick!y as posssible. The work to be performed for seeding disturbed areas includes: