(1) Purpose. The purpose of EC 9.6793 is to protect waterways in the headwaters area from the erosive affects of increases in stormwater runoff peak flow rates and volumes resulting from development.
(2) Applicability and Exemptions.
(a) Except as exempt under EC 9.6793(2)(c), the standards in EC 9.6793(3) apply to all land use applications for development sites in the headwaters area that drain directly into a headwater stream or drain into a pipe that discharges into a headwater stream that are submitted after July 14, 2006 requesting approval of one or more of the following:
1. A cluster subdivision – tentative plan (EC 9.8055);
(b) Except as exempt under EC 9.6793(2)(c), the standards in EC 9.6793(3) apply to all applications for development permits for development sites in a headwaters area that drain directly into a headwater stream or drain into a pipe that discharges into a headwater stream that are submitted after July 14, 2006.
(c) The standards in EC 9.6793(3) do not apply to:
1. A land use application that will result in the construction or creation of less than 1,000 square feet of new or replaced impervious surface at full buildout of the development.
2. A development permit application for any of the following:
a. Development of a lot or parcel included in a land use application that was determined by the city to comply with the standards in EC 9.6793(3). For such a development permit, the approved land use plan shall control.
b. Development of a lot or parcel that was not included in a land use application that was determined by the city to comply with the standards in EC 9.6793(3) and:
(1) Will result in less than 1,000 square feet of new or replaced impervious surface within a 12 month period; or
(2) Is to construct or alter a one or two family dwelling; or
(3) Is for the replacement of more than 1,000 square feet of impervious surface for purposes of maintenance or repair for the continuance of the current function, providing that as part of such maintenance and repair the applicant is replacing less than 50% of the length of the stormwater drainage system (including pipes, drainageway catch basins and drywells) on the development site.
3. Development sites within a drainage basin for which the city has constructed or approved a project to restore the receiving waterway, and the entire downstream system has been designed to accommodate full build-out conditions within the drainage basin.
(a) Applications shall demonstrate, using methodology in the Stormwater Management Manual, that peak rates of flow delivered to an existing open waterway at a point above 500 feet in elevation will not increase during storms larger than the water quality design storm and smaller than the flood control design storm as a result of the development that is the subject of the application;
(b) For purposes of designing the system as required by the standards in this section, the amount of impervious surface per lot is assumed to be the maximum lot coverage allowed for the use in the zone in which it is located, unless the applicant demonstrates otherwise.
(c) All facilities to control the rate of stormwater runoff shall be sited, designed and constructed according to the flow control provisions and the facility design requirements set forth in the Stormwater Management Manual. Flow control facilities must be designed using one of the methodologies outlined in the Stormwater Management Manual.