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i � <br /> i <br /> Reid, Middleton & Associates, Inc. <br /> File No. 02-BS-094 Engineer� • Surveyors • Plonners <br /> Oct�ber 10, 1986 <br /> Revised Jan. 2, 1966 <br /> DOWNSfREAM �S, �TIVE FOR <br /> SILVER I,A[� SII�F SERVICE S1pR1� A�ID CA�Sg <br /> BY PUGET WfST NRYORATION <br /> CITY OF E�/EF22EiT, FIASHINGIC)N I <br /> The existing drainage way, as shown on the City oE Everett Com�rehensive <br /> Drainage Plan Map, northwesterly of this project indicatea a defined drainage <br /> way which discharges into an existing stocm water detentior� facility adjacent <br /> to the southerly right of way of 100th Street extended. We after performing a <br /> field topographic study of the area find the follaving: <br /> 1. �Phe drainage swale westetly of the project site fans out and blends <br /> into the topography within 150 feet northessterly of this project. <br /> 2. The topography north of 16th Avenue extended slopes more abruptly <br /> into t.he same natural drainage way as shown on the City Canp, Plan <br /> Map. <br /> 3. The drainage from the upper reaches of this basin, which are <br /> tributary to this drainage way, are presently either wooded or scrub <br /> undergrowth for ground cover. <br /> 4. The drainage swale westerly of the project does carry water but there <br /> appears to insufficient vol�nne to establish a channel. I <br /> 5. The topographic slopes found in this natural drainage way vary from 3 � <br /> to 10 pa_rcent. <br /> � <br /> 6. The dzainage way is continuous from the proposed rip rap rock outfall <br /> to an existing 12" Culvert which discharges into the detention pond � <br /> mentioned above. The invert of said 12" culvert in the pond is at � <br /> elevation 542.3 (City of EVerett laatum) which is 0.1' above the (' <br /> invert of the 12" outlet in the control manhole. ? <br /> u <br /> 7. Calculating the slope between the proposed outfall and the existing � <br /> 12 culvect in the pond results in the follc�wing: <br /> Difference in elev. 15.31'; Distance 451'± ; Average Slope = 3.398 <br /> Using a 12" concrete culvert as the assim�ed future conveyance Q max. = 6.57 <br /> c.f.s, using D'�nnings Equation and 0.013 for roughness n. <br /> The developed Q froa this project is limited to the discharge capacity of the <br /> outfall culvert. Ttie slope of the 12" concrete culvert as shown on the <br /> enclosed plan is 1.028 with a Q max = 3.91 c.f.s.. <br /> 121 5[li Avenue North, Sui[e 200, Edmonds, Woshing[on 98020 (206) 775-�4�4 <br />