9.23.020 General requirements.
All developments and redevelopments shall make provisions for the control of pollutants in, and the collection, retention and disposal of, storm and other water runoff. The method of storm drainage handling will be dependent on the location of the development or redevelopment, but in all cases shall at a minimum comply with the latest edition of the Stormwater Management Manual for Eastern Washington, and Chapter 6 of the City of Selah’s Design, Construction Standards, and Specifications Manual for Public Works Improvements as adopted in Section 13.01.010.
(1) It is the intent of this section to adequately provide for suitable drainage provision in all short plats or regular subdivisions. All subdivisions shall provide for drainage such that their development does not conflict with present drainage patterns, or create a drainage problem within itself or for its neighbors.
(2) A drainage plan, where required, shall be prepared by a licensed engineer registered in the state of Washington and submitted to the city for review and approval for any proposed land development or redevelopment that will increase the quantity of or in any way alter the drainage runoff occurring prior to development or redevelopment.
(3) Design calculations for peak flow and peak volume storage requirements shall be in accordance with the provisions of the latest edition of the city of Selah Construction Standards for the Private Construction of Public Facilities unless it is determined by the city that the development or redevelopment is located in a drainage problem area, whereby the design storm frequency, or other design parameters, may be adjusted as required to address the drainage problem.
(4) The drainage plan shall provide for the on-site detention and/or retention of the total water intercepted and collected by the development or redevelopment and the areas (improved or unimproved) lying upstream and drainage presently to and through the proposed development or redevelopment, for the design storm, unless other natural or manmade systems are available for use.
(5) Detention and/or retention of storm water runoff from any proposed land development or redevelopment shall be accomplished by storm water holding facilities either open or closed or by introduction, on site, of storm water into permeable soils via an infiltration system.
(6) The drainage plan shall incorporate all calculations required by and in the latest edition of the city of Selah Construction Standards for the Private Construction of Public Facilities. Collection systems shall be either gravity pipe systems, open channels, or a combination of the two.
(7) The overflow of runoff in excess of the design storm quantities must be situated or directed to where it would have overflowed under the conditions existing prior to proposed development or redevelopment. The capacity of the drainage course downstream of the development or redevelopment may be required to be evaluated. The submitted drainage plan shall incorporate, among other data, a topographical map to clearly define:
(A) The proposed development or redevelopment;
(B) All areas, improved or unimproved, lying upstream and drainage to and across the proposed development redevelopment; and
(C) Drainage course, natural or otherwise, to which the proposed development or redevelopment shall drain.
(8) The plans shall be prepared in accordance with the latest edition of the city of Selah Construction Standards for the Private Construction of Public Facilities. (Ord. 2081, § 4, 2019; Ord. 1799, § 1, 2010.)