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why significant modifications to the ditch geometry (triangular versus trapezoidal) were <br />instituted during construction. <br />During construction of the ditches, it was determined that roughly triangular ditches could be <br />built that would convey surface water runoff as effectively as the designed trapezoidal ditches <br />with a smaller total surface footprint. <br />4. The as -built designs refer to segments of ditch having been lined with 3" and 6" riprap. <br />During numerous site inspections, Division personnel have not observed that riprap of <br />any size has been used to armor the NHN -001 East and West collection ditches. Please <br />revise the application to accurately portray and evaluate the armoring system used for <br />certain segments of these ditches. <br />The Geoweb material used in the ditches feeding Pond NHN -001 is used as an alternative to <br />standard riprap. See the photo below: <br />z' <br />The Geoweb is staked in place atop of filter fabric. It allows the usage of general rock as <br />substitute for layered riprap. Appendix 2.05.3(4) -7 contains more information such as a <br />standard installation detail, and a technical evaluation from Colorado State University <br />showing the velocity tolerance of the Geoweb when used with aggregate. <br />