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In areas \\l1ere a FEMA f100dway exists, increases in the 100-year water-surface elevation are not allowed above the established 100-year maximum water surface elevation. Once the FEMA 100-year floodway limits has been established, no further infringement will be allowed. 2.5 Detention Storage of Storm Water Runoff 2.5.1 On- and Off-site Regional Detention Basins Regional detention basins or other structures can be used to maintain historical runoff flows. Care must be taken to design and construct all such facilities in accordance with applicable federal, state and local regulations. Detention ponds may be required to reduce peak flows when existing facilities are unable to handle the increased peak flow resulting from a proposed development. The drainage masterp1anning process shall identify alternatives with regard to improvement of downstream facilities or providing on-site detention. The initial burden of cost for either alternative shall be born by the developer (see Chapter 4 - Financing of Drainage Improvements). The costs of constructing the storm water detention pond, including the safety features, will be e1 i gi b 1 e for reimbursement in accordance with the provi s ions for reimbursement or credits contained in 15-3-907 of the Code of Colorado Springs, 1980, as amended or Section 49.3D of the Land Development Code of E1 Paso County, 1985, as amended. 2.5.2 Open-channel Storage Open-channel storage is addressed in Section 2.2.2. 2.5.3 Volume and Release Requirements Storm water detenti on ponds shall be sized by the ~oodwR'IlIJti ngProcedure! as outlined in Chapter __ of the Drainage Criteria Manual. The design storms for the computati~of storage volume r~irements for detention ponds shall be the SCS 10-year, JlLhour and 100 year, ~hour storm. The storm water detention pond emergency spillway shall be designed to pass the maximum peak discharge for a 100 year storm without damage to the structure, assuming the outlet structure is totally inoperative and the upstream watershed is fully developed. No buildings or structures shall be constructed in the limits of the 100 year storm discharge. All storm water detention ponds which fall under the jurisdiction of the state, shall be designed using the state criteri a. Detention storage areas shall have designed volume requirements compatible with release rates that wi 11 not exceed the natural runoff rate or capacity of downstream facilities. The design of all impoundments which meet specifications for a dam, whether temporary or permanent, must be submitted to the State Engineer of Colorado. 2-5 I I I I I I I I I I I I I I I I I I I