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<br />-3- <br /> <br />greater than 64 acres in size. The zone line shall be <br />del ineated parallel to the Blanco River and Sink and <br />Purgatory Creeks or their tributaries according to the <br />size o~ the drainage basin: <br /> <br />(1) For tributaries of the Blanco River, Sink and <br />Purgatory Creeks, the zone line shall be defined <br />by the limits of the 100-year flood plain, <br />provided that it shall never extend beyond 100 <br />feet on each side from the centerl ine of the <br />,.....Ia terway. <br /> <br />(2) For the main channels of the Blanco River, SinK and <br />Purgatory Creeks, the zone line shall be defined by <br />the 100-year flood plain; provided that it shall <br />never be located greater than 200 feet from the <br />centerline of the waterway. <br /> <br />b. <br /> <br />The flood plain delineation shall be based on the <br />latest City adopted Federal Emergency Management Agency <br />(FEMA) map or those provided and certified by a <br />registered professional engineer as provided below. <br /> <br />(1) If FEMA maps are not adopted for a tributary, or if <br />the developer choses not to use FEMA maps the <br />flood plain shall be determined by a registered <br />professional engineer. In this event, a map of the <br />flood plain and the calculations used to determine <br />the flood plain shall be provided by the engineer <br />with the plat of the subdivision when the plat is <br />filed with the Planning Commission. <br /> <br /><2) If the flood plain del ineation is determined by an <br />engineer, such delineation shall be subject to <br />approval by the City Engineer. <br /> <br />(3) The flood plain del ineation shall be based on a <br />channel in its unaltered state, and shall assume <br />existing development watershed conditions. <br /> <br />(4) Maps showing the flood plain within a subdivision <br />shall be provided with the plat at a scale of 1 <br />inch to 200 feet and shall be signed and sealed by <br />a registered professional engineer. <br /> <br />c. <br /> <br />Recharge structure Critical Water Quality Zones are <br />hereby establ ished within a 25 foot radius of the <br />openings, extremities, or extremities of the depression <br />at the ground surface, whichever is the larger area, of <br />a surface recharge structure such as a cave opening, <br />sinkhole, open fracture, and within 100 feet of the <br />recharge structure's extremities at the surface <br />within the recharge structure drainage area. <br /> <br />d. <br /> <br />The Critical Water Qual ity Zone shall remain free of <br />all construction activity, development, impervious <br />cover and alterations except that the following may be <br />perm i tted: <br /> <br />(1) Arterial, collector and residential <br />crossings only as provided below: <br /> <br />street <br /> <br />(a) The main channel of the Blanco River, SinK and <br />Purgatory Creeks may be crossed by arterial <br />streets, provided, however, that no arterial <br />street crossing shall be within 2,000 feet of <br />any other crossing of a collector street or <br />arterial street on the same waterway. <br /> <br /><b) Tributaries may be crossed by arterial and <br />collector streets, provided, however, that no <br />collector street crossing shall be within <br />2,000 feet of any other crossing of a collector <br />street or arterial street on the same waterway. <br /> <br />(c) Tributaries may <br /> <br />be <br /> <br />crossed <br /> <br />by a <br /> <br />residential <br />