1710 W MARINE VIEW DR 2024-01-03

BMP C202: Riprap Channel Lining Purpose To protect channels by providing a channel liner using riprap. Conditions of Use Use this BMP when natural soils or vegetated stabilized soils in a channel are not adequate to pre- vent channel erosion. Use this BMP when a permanent ditch or pipe system is to be installed and a temporary measure is needed. An alternative to riprap channel lining is BMP C122: Nets and Blankets. The Federal Highway Administration recommends not using geotextile liners whenever the slope exceeds 10 percent or the shear stress exceeds 8 Ibs/ft2. Design and Installation Specifications . Since riprap is typically used where erosion potential is high, construction must be sequenced so that the riprap is put in place with the minimum possible delay. . Disturb areas awaiting riprap only when final preparation and placement of the riprap can fol- low immediately behind the initial disturbance. Where riprap is used for outlet protection, the riprap should be placed before or in conjunction with the construction of the pipe or channel so that it is in place when the pipe or channel begins to operate. . The designer, after determining the riprap size that will be stable under the flow conditions, shall consider that size to be a minimum size and then, based on riprap gradations actually available in the area, select the size or sizes that equal or exceed the minimum size. The pos- sibility of drainage structure damage by others shall be considered in selecting a riprap size, especially if there is nearby water or a gully in which to toss the stones. . Stone for riprap shall consist of field stone or quarry stone of approximately rectangular shape. The stone shall be hard and angular and of such quality that it will not disintegrate on exposure to water or weathering and it shall be suitable in all respects for the purpose inten- ded. See Section 9-13 of WSDOT's Standard Spec cations for Road, Bridge, and Municipal Construction (WSDOT, 2016). . A lining of engineering filter fabric (geotextile) shall be placed between the riprap and the underlying soil surface to prevent soil movement into or through the riprap. The geotextile should be keyed in at the top of the bank. . Filter fabric shall not be used on slopes greater than 1.5H :1 V as slippage may occur. It should be used in conjunction with a layer of coarse aggregate (granular filter blanket) when the riprap to be placed is 12 inches and larger. 2019 Stormwater Management Manual for Western Washington Volume 11 - Chapter 3 - Page 337