11/12/1991 - Laserfiche WebLink

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r I 84 F -L 778 that the county landfill can accommodate the additional solid waste. -Drainage Because of the drainage characteristics existing in this area, the county -engineer has indicated that special drainage conditions should be applied to any single family residential building permit approval in this area. These conditions which will be applied to each lot at the time of the single family concurrency review will specify that the applicant shall use shallow swales to collect and store''runoff from the site for attenuation and .treatment purposes prior to direction to the canal system. so as to eliminate standing nuisance water in inappropriate areas. With these conditions, 48 All developments are reviewed for compliance with county stormwater regulations which require on-site retention and minimum finished floor elevations. In addition, development proposals will have to meet the discharge requirements of the county Stormwater Management Ordinance. Since the subject property is located within the M-5 Drainage Basin and no discharge rate has been set for this basin, any development on the property will be prohibited from discharging any run-off in excess of the pre -development rate. In this case, the minimum floor elevation level of service standards do apply, since portions of the property are located within a floodplain. As per Drainage Objective. 1, as well as Drainage Policy 1.1, "New development requiring major site plan approval or subdivision platting shall construct a complete drainage system to mitigate the impacts of a 25 year/24 hour design rainfall using the Soil Conservation Service. Type 2 Modified Rainfall curves. Post development runoff shall not exceed pre - development runoff unless a maximum discharge rate has been adopted for the applicable drainage basin and the discharge does not exceed ' :that rate." Consistent with Drainage Policy 1.2, "All new buildings shall have the lowest habitable floor elevation no lower than the elevation of the 100 year flood elevation as shown on the Federal Emergency Management Agency (FIRM) or as defined in a more detailed study report." Parts of the site, especially along the ditches, are located within Flood Zone A, which is a special flood hazard area located within the 100-yearfloodplain. No minimum elevation standard is ` specified for the A flood zone on the Flood Insurance Rate Maps for this portion of the county. The remainder of the property is `r located in Flood Zone X, which is located outside the 500 -year floodplain and is classified a minimal flood zone area. Both the on-site retention and discharge standards of the drainage - sub -element also apply to this request. With the most intense use ,Frrq ¢ of this site, the maximum impervious surface area for the proposed'=: request will be 890,000 square feet. The maximum run-off volume �- 'for the design storm, based upon the amount of impervious surface,-.rr�_' will be 5,000 cubic feet for each unit or 890,000 cubic feet for'. �.:. the total 178 units. In order to maintain the county's adopted,,' level of service, the applicant will be required to retain 74,000 cubic feet of run-off in swales. It is estimated that the pre- development,run-off rate is 24.25 cubic feet per second. Based upon staff's analysis, the 'drainage level of service standards will be met by limiting off-site discharge to its pre - development rate of 24.25 cubic feet per second and requiring retention of the 74,000 cubic feet- of run-off for the most intensive use of the property. Since no minimum floor elevation ha"s been established in this area on the FIRM maps, the level of service standards for minimum floor elevation will be met at the time of building permit approval. At that time the lowest habitable floor elevation, consistent with Drainage Policy 1.2, will be determined by the design engineer and approved by_the building department. - Because of the drainage characteristics existing in this area, the county -engineer has indicated that special drainage conditions should be applied to any single family residential building permit approval in this area. These conditions which will be applied to each lot at the time of the single family concurrency review will specify that the applicant shall use shallow swales to collect and store''runoff from the site for attenuation and .treatment purposes prior to direction to the canal system. so as to eliminate standing nuisance water in inappropriate areas. With these conditions, 48