09-20-1982 Planning Packet - Laserfiche WebLink

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Local Standards (Continued) by the land parcel in Itt pre-develop- ed conditioo. AdnMedy, this strict standard may be difficult to achieve on very smaU parcels arwl other existinQ situations. Howvever. most developments of all acaloii con meet this reouirement, often with substantial savings in con- stniction costs. (For a thorough over view of the available technology, ^ Tourbier and Westmacott Water Re sources Protection Technology, published by the Urban Land Insthute.) In the MeticpoStan Tvdn Cities, wa ters hed dtatricts have inipcMod this Rmit on runoff vrith good succe ss. Many site ptanners and devdop« around the country would vwnrtgly design for natural dtainaga, but are frustrated by local insisiance ondeslgn Standards which make natural drainaQa needlessly costly or impossible to achieve. Such limitations include: re quired excess pavement vvidths, re- Quired curb and outter, iTOrsmuin permitted overland flow, and required storm sewerage. Al have been into the fabric of our dtarking with threads of steel,, but really don t make any sense In most suburban communities. In a recent joint study by the Association of Metropolitan Commu nities and the Metropolitan Council (The Cost of Public Services for Housing, 1981). street pavement widths required by most Metro-area communities were found to be ex cessive when compared to national aources and standards. Excessive pav ing for roads and sidewalks needeaaly cuts down the area available for runoff to soak into the ground. Groundwater recharge capacity is lost and runoff is increased. The extra paving raises developmem costs and city maintenartce and replaceniont commitments need le ssly- At a time when 1/42nd of every barrel of imported oil goes for asphalt paving, extra paving adds to our nations energy problems. The decision as to whether to use curb and gutter on new streets is pivotal to the choice bet ween fast versus slow nmoff drainage systems. Curb and gutter concentrates and contains water on the road surfaM requiring storm sewers and dr^ inlets to dear runoff water from it. Storm sewers ore clearly fast runoff systems. Most communWes <k> not undersmd that curb and gutter str^ make natural drainage ^ possible to achieve. This o**^®J*° Supported in The Co« o1 Public Services for Housing (Cited earlier) where 98% of the corr«wi^««^ veyed stated that they allowed storm iwater drains where Yet, 74% these sairte cocnmunities always required curb arrd gutter, making natural drainage impractical. Apparently, the curb and gutter detail is thought to serve more than A word about non-dr atnage uses for curb and gutter: nonsense. The standard uses named indude snow plow and traffic guides, pedestrian protection, and road edge stability. The facts do not support those claims All of these functions are, at best, poorly addressed by curbing and can be much better fulfilled by good site planning and other design dements at much lower costs. 11 1 J-i - ■y . .,4 SebSykM The third major area in which wo can make changes to benefit frtw naturd drainage is to encourage the detention of vi«ter on-site through the use of ponds and ponding sys tems. VWhh a smaB amount of cia^ design, such ponds can greatly ^ runoff through 8 tompofsry holding action vwhao adtSng amenity and value to the subdivision. Such ponds an most accurately designed and easily evduated using Oottirtg the Most Out of Your Raindrop Hydrology Guide for Minnesota, public by the U.S.D.A. Soil Conseniation Ser vice in St. Paul. Minnesota. It ^ be obtained free through yw County Soil Conservation Service office. This publication and others by the S.C.S. .will enable your commun^ to step away from the outdated "Rationd MdhodT' of computing stoim nmoff (the standard in m<^ a drainage function. In fact, the curb was originally developod as a drainage control device for intense urban en vironments where drainage ditches took up too much horizontal space. Most modem suburban zoning re gulations have eliminated that problem. Today, suburban streets have the horizontal space adjacent to tt^ to accomodate grassy drainage «twes. Such ditches slow nmoff as vnell m mtpoaa it to percolation into the ground and evaporation due to ex posure to the sun. Drainsge swales are much cheaf» to build than curb and gutter ^ its associated storm sewers. In just curb and gutter alone the construc tion savings is «.00 per lineal foot (11.40 of vdiwh is directly r^ed to energy costs). As a drainage device, grassy ditches are dear win ners over curbs artd gutter. Thu^ for natural drainage, elin*iate curb and gutter. runon tine sianoaiw im _« ing and municipal engktesnng off*®^ The Rational Method typicaUy rewto _________M mH o\msi2adin poor pond design »id overdzed systems. Ponds that work bettor low better and make a positive contri bution to the community. The S.C.S. is one of the best fiiara* for communitieB artd develops to turn for guidance in dovolopl^ and revievring proposals fix naturd drainage systems. Tfw free of charge and the S.C.S. «»- qineers are especially expert in tfw urban applications of the r^ural "slow run^' approach to designing drdnage systems. Natural drainage is a system tw has been generated by lepetrthw trial and field tested for thousands of years. Why not try it in your community? Remember, its not eco nomical to fight Mother Nature.