3900 BROADWAY BASE FILE 2016-01-01 MF Import

CITY OF EVERETT STORMWATER MANAGEMENT MANUAL Maintenance Sfandards , 1. During thc establishment period,check grazs-lined channels aRer every rainfall. 2. After grass is established,periodicelly check the channel;check it aRer every heavy rainfal� event. Immediately make repairs. 3. It is pazticularly importanl ro check the ch�mnel outlet and all road crossings for bank stabiliry and evideoce of piping or scour holes. 4. Itemove all significant sediment accumulations to mxintain thc designed cartying capacity. Keep the grass in a healthy,vigorous coodition at all times,since it is the primary erosioo proteciion for the c6annel. 3.3.3 BMP C202: Channel Lining Purpose To protect erodible channels by providing a channel liner using either blankets or riprap. Condifions of Use When nahtral soils or vegetatcd stabilized soils in a c6ennet are not adequate to provent channel emsion. 1. Wheu a permanent ditch or pipe system is to be installed and a temporary measurc is oeeded. 2. In almost all cases,syut6etic and organic coconut blankets are more effective than riprap for protecting channels from erosion. Blenkets can be used with and without vegetation. Blanketed channels can be designed to handle any expected tlow and longevity requirement. Some synthetic blankets have a predicted life span of 50 yeazs or more,even in sunlight. 3. Other reasons why blankets are better than rock include the availability of blankets over rock. In many azeas of the state,rock is not easily obtainable or is very expensive to haul ro a sitc. Blankets can be delivered anywhere, Rock requires the use ot dump Wcks to haul and heavy equipment to place. Blankets usually only rcqu'vc laborers with hand tools,and somctimes a backhoe. 4. T6e Federal Highway Administration tecommends not using flexible liuers whenevcr the slope exceeds 10 percent or the shear sh�ess exceeds 8 powdslsquare foot. Deslgn and lnstallation SpeciRcatlons I. Sce BMP C122 for infortnation on blankets. 2. Since riprap is used where erosion potential is high,constniction must be sequenced so that the riprap is put in place with the minimum possiElc delay. 3. Dislurbance of azeas wherc riprap is[o bc placed should be undertaken only when final preparation and placcment oF the riprap can follow immediately behind t6c initial disturbance. Where riprap is used for outlet protection,the ripnp should be placed beforc or in conjunction with the conshuction of the pipe or channel so that it is in place when the pipe or channel bcgins to operatc. 4. Thc dcsigner, aftcr detertuining the riprap sizc that will bc stable under thc flow conditions,shall consider that size to be a minimum size and then,based on riprap gradations actually available in the arca,select the size or sizes that equal or excecd the minimum sizc. The possibility of drainage structure damage by children shall be considered in selecting a riprap size,especially if there is neazby water or a gully in which to toss the stones. Vofume II—Consiruction Stormwater Pollufion Prevention 3-39