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SUBDIVISION <br /> 4. Detention pond bottoms must be vegetated. K. Conformance with the City's Stormwater Technical <br /> Manual.All stormwater facilities,including those for low <br /> G. Waiver of Detention/Retention. impact development,detention, retention or water quality, <br /> 1. Detention/retention may be waived for non-residential shall be designed by a licensed professional engineer in <br /> small site permits if no adverse impacts are demonstrated accordance with the City's Stormwater Technical Manual, <br /> through drainage analysis and a payment-in-lieu is made including requirements for location, screening and fencing <br /> into the stormwater management fund in accordance with not inconsistent with this Chapter and applicable ordinances. <br /> Section 6.1.1.3. All plans submitted to the Responsible Official for approval <br /> shall include a layout of the stormwater management system <br /> 2. Detention/Retention may be waived in High Intensity together with supporting calculations for the design of the <br /> Zones if no adverse impacts are demonstrated through system. <br /> drainage analysis and a payment-in-lieu is made into the <br /> stormwater management fund in accordance with Section Section 3.9.1.2 Velocity Attenuation and Surface Drainage <br /> 6.1.1.3. Channels <br /> H. Street Drainage.Except for inverted crown thoroughfares, no A. Surface Drainage Channels.Surface drainage channels <br /> lowering of the standard height of street crown shall be allowed constructed or altered for drainage purposes shall be designed <br /> for the purposes of obtaining additional hydraulic capacity. to minimize potential erosion and to increase the bottom width <br /> Bridges and culverts in residential streets, shall be designed to flow depth ratio as follows: <br /> for the runoff from the one hundred (100)year frequency 1. Channel cross sections shall be trapezoidal in <br /> flow based on a fully developed watershed.shall not produce configuration; <br /> a headwater depth at the roadway greater than either twelve <br /> (12) inches above the roadway crown or any top of upstream 2. Side slopes of channels shall be no steeper than four <br /> curb elevation,whichever is lower. For bridges and culverts horizontal to one vertical; and <br /> in streets other than residential areas,the one hundred (100) <br /> year headwater depth is limited to six(6) inches. Storm drain 3. All constructed and altered drainage channels shall be <br /> system shall be designed to meet the criteria listed in the stabilized and vegetated as soon as practicable after final <br /> Stormwater Technical Manual. grading. <br /> I. Minimize Cut and Fill.The layout of the street network, lots 4. Channel velocities shall be non-erosive. <br /> and building sites shall minimize the amount of cut and fill on B. Additional runoff velocity attenuation strategies and techniques <br /> slopes in accordance with the standards for cut and fill set detailed in the City of San Marcos Stormwater Technical <br /> forth in Section 6.1.2.2. Manual shall be utilized. <br /> J. Permit Required.No person,individual, partnership,firm Section 3.9.1.3 Impervious Cover Calculation and <br /> or corporation shall deepen,widen,fill, reclaim, reroute or Limitations <br /> change the course or location of any existing ditch, channel, <br /> stream or drainage without first obtaining a site plan permit and Paved roads, sidewalks, parking areas, parking lots, buildings <br /> permits from applicable agencies (such as FEMA or the U.S. and other impermeable construction covering the natural land <br /> Army Corps of Engineers) having jurisdiction.The Responsible surface shall be considered impervious cover.The methods to be <br /> Official may, at his or her discretion, require preparation used to calculate the percent of impervious cover created by the <br /> and submission of a FEMA or flood study for a proposed development of a parcel or tract of land are described in the City <br /> development if there are concerns regarding storm drainage Stormwater Technical Manual. Note that the area of impervious <br /> on the subject property or upstream or downstream from the cover for a surface may be reduced based on data acceptable to <br /> subject property.The costs of such study, if required, shall be the Responsible Official showing that the surface has a significant <br /> borne by the developer. degree of permeability. <br /> 3:58 San Marcos Development Code Adopted April 17,2018 <br />