City of Fredericksburg, Texas STORM WATER DETENTION ORDINANCE August 4, 1998 1.0 Purpose and Applicability 2.0 Standards and Requirements for Storm water Detention 3.0 Regional Detention Pond Program 4.0 Standards and Requirements for Erosion/Sediment Controls 5.0 Additional Standards for Approval -
1.0 Purpose and Applicability a) The growth in and around the City of Fredericksburg and the associated development and construction of buildings, paved surfaces, roads and other improvements has altered in the past and continues to alter the natural flow of surface waters on the land, which together with the construction of gutters, culverts, drains and channels for the carrying off of surface waters has both increased the quantity of storm water and amplified the peak flow rates of runoff, thus leading to present and potential flooding of property and homes, dangerous flows within and over public roadways and streets, and soil and channel erosion. b) It is the intention of the City Council to protect the health and safety of the citizens and visitors of the community and to prevent damage to private property and public facilities through the proper design and construction of both on-site and regional storm water detention facilities that prevent or adequately reduce increases in peak flow rates of runoff that may otherwise increase the risk of flooding and the associated risk of public endangerment, property damage and erosion. c) It is the intention of the City Council, through this Ordinance, to establish a regional storm water detention pond program for the design and construction of regional storm water detention facilities so that, where practical, the most cost-effective protection from flooding may be accomplished. d) It is the intention of the City Council to protect the health and safety of the citizens and visitors of the community and to prevent damage to private property and public facilities through the installation and use of temporary and permanent erosion control practices that prevent or adequately reduce increases in erosion and siltation that may otherwise increase the risk of flooding and the associated risk of public endangerment and property damage by clogging and/or partial filling of constructed or natural drainageways as well as drainage structures and detention ponds. e) This Ordinance shall apply to all property within the corporate city limits and the Extra-Territorial Jurisdiction (ETJ) of the City unless otherwise stated. f) Section 2.0.b and 4.0 of this Ordinance shall not apply to: 1) Single family or duplex residential lots, of subdivisions approved prior to the adoption of this Ordinance, unless specifically required by prior agreement between the City and the owners or developers of such subdivisions, or to new one- or two-lot subdivisions for single family or duplex residential lots, and this Ordinance is intended to be implemented for entire subdivisions at the time of platting and construction of street and drainage improvements and not on an individual lot basis for single family and duplex residential subdivisions. 2) Residential lots in the ETJ that creates no more impervious ground cover than twenty percent (20%) of the gross lot surface area exclusive of any area within the one hundred (100) year flood plain. 3) Multi-Family or Non-Residential lots less than one-half (½) acre.
BACK TO TOP 2.0 Standards and Requirements for Storm water Detention a) It is prohibited to place fill material or construct impervious cover or construct or place any other structure on such person’s property or perform any excavation or grading in a manner which alters the flow of surface water across said property in a manner which damages any adjacent property. 1) No final subdivision plat, subdivision construction plan, site plan or building permit shall be approved by the City unless it can be demonstrated by the owner or developer of such property that the proposed development will not result in damage to any adjacent or downstream property. This will be certified by a professional engineer’s submittal of sufficient data and calculations.
b) The above requirement shall be accomplished through one of the following means: 1) Design and construction of an on-site storm water detention facility, or facilities, by the land owner or developer which limits the peak flood flows from the proposed development to the existing peak flood flows from the subject tract. 2) Construction of, or participation in the construction of, off-site drainage improvements, such as storm inlets, storm sewers, culverts, channel modifications, land filling, and/or other drainage facilities such that the peak flood flows for fully-developed watershed conditions form the watershed area in which the proposed development is located will be sufficiently and safely passed without flooding of adjacent and downstream property and roadways. 3) Design and construction of the development by certified engineering data and calculations utilizing limited impervious cover, infiltration of runoff from impervious cover via flow through pervious areas, and/or grass-lined swales or channels such that these measures result in a minimal increase in peak flood flows from the development.
c) Acceptance of requests from the land owner or developer to meet the storm water detention requirements through measures listed in Items 2.b.2 and 2.b.3 above is solely at the discretion of the City and shall not relieve the owner of responsibility under civil law to adjacent and downstream properties. d) Acceptance by the City of on-site storm water detention plans will be based on the suitability and adequacy of the engineering and technical design of the proposed storm water detention facility, as described in Section 5.0 below.
BACK TO TOP 3.0 Regional Detention Pond Program a) The City hereby establishes the Regional Storm water Detention Pond Program whereby the City will design and direct construction of or otherwise facilitate construction of regional storm water detention ponds in order to prevent increases in and, if practicable, to reduce peak flows or storm water runoff.
BACK TO TOP 4.0 Standards and Requirements for Erosion/Sediment Controls a) No final subdivision plat, subdivision construction plan, site plan or building permit shall be approved by the City unless the plans for the proposed development include temporary and permanent erosion and sedimentation control measures such that siltation of downstream drainageways are minimized. b) The above requirement shall be accomplished through a combination of the following practices: 1) Installation of silt fences and rock berms before and during construction in order to reduce on-site soil erosion and provide temporary capture of sediment. 2) Temporary and/or permanent revegetation of bare ground in order to stabilize disturbed soil at the earliest practicable date. 3) Construction of on-site storm water detention facilities by the land owner or developer in a manner such that detention ponds function as temporary sedimentation basins until permanent revegetation of the subject tract is accomplished. 4) Other measures which may be necessary to control erosion and sedimentation on a site by site basis.
BACK TO TOP 5.0 Additional Standards for Approval a) A Registered Professional Engineer, licensed in the State of Texas and qualified and experienced in the design and operation of storm water detention ponds and related storm water management facilities, shall perform the hydraulic and structural design of storm water detention ponds and related storm water management facilities, including the development of engineering and technical information required for evaluation by the City. b) All design and technical information necessary to thoroughly evaluate the suitability and adequacy of the engineering and technical design of proposed on-site storm water detention facilities and, if proposed, off-site facilities shall be provided to the City for review. All detention and runoff calculations, including computer model simulations, if used, shall be provided. c) All on-site storm water detention facilities shall be designed to adequately and safely pass all storm water inflows, including flood flows and runoff from upstream and adjacent properties that have natural and/or existing overland flows toward and onto the subject tract. The on-site storm water detention facilities should not impound storm water onto or cause backwater to inundate any upstream or adjacent properties in excess of existing conditions. d) On-site storm water detention facilities shall not be placed such that they encroach into the regulatory 100-year floodplain as established by the City, Gillespie County, and/or the Federal Emergency Management Agency, unless it can be satisfactorily demonstrated to the City through the use of hydraulic modeling that such encroachment will not cause any rise int the 100-year flood level on other off-site properties or that the increase in the 100-year flood level caused by such encroachment will occur entirely onsite on the owner’s or developer’s property. e) Additional engineering and technical rules and guidance with respect to the application and review of the stormwater detention requirements of this Ordinance may be provided by the City within a Drainage Criteria Manual. f) All design and technical information necessary to thoroughly evaluate the suitability and adequacy of proposed erosion and sedimentation control measures shall be provided to the City for review. g) Additional rules, guidance and requirements with respect to the review and acceptance of temporary and permanent erosion and sedimentation control plans may be provided by the City within a Drainage Criteria Manual.
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