10011 3RD AVE SE BASE FILE 2016-01-01 MF Import

� ' A conceptual plan is described for deveioping an enhanced drainage swale that incorporates the undisturbed ponion of the existing isolated wetland, includes tlow t control strucmres, and is enhanced with native plant species. 77ie intent of the enhanced swale is to provide habitat for passerine birds,convey storm wacer runof(, and improve water qualiry. 'll�e swale would be five to ten wide, and meander ' through thc 24toot drainage eazement along the south properry line and through thc outer ponion of the buller along the stream corridor. This would provide over 800 (eet of enhanr:ed Jrainage swale enconpassing about 0.2 acres. 'fhe swale would , be wnstructed in two types: conveyance channel and infiltration ditch. Although the swale will need to be specifically engineered, the following describes how the swale will be rnnstructed and function. ' The mnveyance channel portion of the swale would begin in the southeazt comer of the property where the on•site storm drainage system outict will be located. The ' drainage would be conveyed into the existing undisturbed portion of the isolated wetland. A control strucmrc would need to be placed at the western edge of the weUand to control drainage on to the neighboring parcel. Other log or rock weir t wntrol strucwres would need to be placed at strategic loca�ions to facilitate slopc and swale gradients. This portion of ihe swalc would be about 300 feet in length. As the swale reaches the native growth bu((er, it w�ll Wrn norlhwesterly aad be t located along the outer edge of the bu(fer. At this point the swale will be deveioped into an infiltration ditch ocarring parallel to the topography. Functioning as an infiltration ditch,storm water would be hcld behind a small berm, and during peak 1 evems, would sheet tlow over the berm into thc farested buffer. M emergenry control strucmre would be lacated at the terminus of the infiltration ditch for extremely high flows. A detailed landscape plan will be developed. The infiltration 1 portion of the enhanced drainage ditch would be 500 feet in Iength. A conceptual planting list and approach is described below. ' A variety of native trees,shrubs and ground covers could be planted to enhance the character and functioning o(the proposeJ swale. Two distinct planting zones would occur in the swale: swale bottom and swale side•slopes. The swale bottom would ' be seasonally inundated and remain saturated into the early summer months. The swale would most likely bccome dry during the late summer months. To lengthen the saturation period in the bottom o(the swale,the swale could be over-excavated � and replaced with a organic peat soil to better retain moiswre. Control swctures rnuld be installed to provide a small amount o(dead storage,and where placed in combination with organic soil deposits,would facilitate development of water regime , suitable Eor supporting hydrophytic planu into the summer mon�hs. Native plants that could be planted in the swale bottom might includc willow,red•osier dogwood, slough sedge,soft rush,small-(ruited bulrush,creeping buttercup,and a hydromulch , rnmprised of ineadow or red fescuc, redtop benigrass, and smartwecd. 71ie side•slopcs o(the swale would be comprised of well-drained soils and would not support a water regime suitable for hydrophyte plant spccies. The opportuniry does texist �o plant a variety of trces and shrubs. These plantings may include westem ' ' �