R655-11-6D. Internal Erosion Control

  A. All dams should have design provisions for controlling internal erosion. In zoned dams all adjacent zones must meet filter criteria with the abutting zones and foundation soils. If filter criteria cannot be met, a transition zone must be provided.

  B. All filter and drainage zones in a dam must meet criteria acceptable to the State Engineer.

  C. In designing filter zones where dispersive clays or broadly-graded materials exist, special considerations may be imposed by the State Engineer.

  D. All chimney filter and drainage zones will have a minimum width of three feet per zone unless waived by the State Engineer. Wider zones are encouraged. Chimney drains may be vertical or inclined, but inclined drains may require additional width. In active seismic areas filter widths must be at least twice the predicted lateral deformation resulting from an earthquake.

  E. Proper filtering and drainage is essential in all dams where cracking from differential settlement, hydraulic fracturing, or earthquake shaking is possible. Chimney, blanket, and toe drains are considered to be standard design measures. Justification must be provided if these features are not included in the design. Other filter and drainage features may also be appropriate.