§ 8.10. Storm water management.
8.10.01. Detention of Excess Storm Water Runoff: Each development shall provide for the on-site or off-site detention of excess storm water runoff resulting from that development. For the purpose of this Article, "excess storm water runoff" shall include all increases in storm water resulting from: an increase in the impervious surface of the site, including all additions of buildings, roads, and parking lots; changes in soil absorption caused by compaction during development; modifications in contours, including the filling or draining of small depressed areas, alteration of drainage ways, or re-grading of slopes; destruction of forest; alteration of drainage ways or installation of collection systems to intercept street flows or to replace swales or other drainage ways; or the alteration of subsurface flows, including any groundwater dewatering or diversion practices compared with the site in its natural state.
8.10.02. Limitation on Storm Water Runoff: No development shall cause downstream property owners, water courses, channels, or conduits to receive storm water runoff from proposed development than would have resulted from the same storm event occurring over the site of the proposed land use with the land in its natural, undeveloped condition. For the purposes of this Article, "undeveloped condition" shall mean that all natural retention areas and drainage ways plus existing farm or highway drainage structures shall be included in the flow calculation, all ground covers shall be considered to be meadow or grassland, with the exception that forested areas shall be treated as woodlands. "Channel" or "drainage way channel" shall mean the channels used to convey the 100-year drainage flows between successive retention facilities or to retention facilities from the property.
8.10.03. Storage capacity: All storm water storage facilities shall be designed with sufficient capacity to accommodate all runoff caused by the development in excess of the runoff which would have resulted from the site if left in its natural, undeveloped condition. The storage capacity of all storage facilities shall be sufficient to store in excess of the excess flow, in each watershed, which would result from the 100-year storm of 24-duration.
8.10.04. Design and Construction of Storm Water Detention Structures: The design and construction of Storm Water Detention systems and structures shall conform to the provisions of the Dickinson Bayou Watershed Regional Drainage Plan — Drainage Criteria Manual for Galveston County, Texas and Texas Water Development Board, August 1992 Edition.
8.10.05 Design Regulations: All detention facilities and improvements required by this Section shall comply with the following regulations.
A.
Storage Volumes: Storage may be provided by wet or dry bottom basins or reservoirs or rooftop storage facilities.
B.
Maximum Depth: The maximum planned depth of stormwater stored shall not exceed five (5) feet unless natural ground conditions lend themselves to greater depths.
C.
Outlet Control Structures: Outlet control structures shall be designed as simply as possible and shall operate automatically. They shall be designed to limit discharges into existing or planned downstream channels or conduits so as not to exceed existing flow of the site in its natural condition.
D.
Spillway: Emergency overflow facilities shall be provided unless inflow is controlled to divert flows when the basin is at capacity.
E.
Fencing Required: A minimum 4-foot high fence is required along all sides of the detention basin with slopes that are greater than 2:1 or have a vertical wall.
1.
Fences should not have any opening greater than four (4") inches.
2.
Fences shall provide a self-latching locked gate which provides access to the pond for use by emergency vehicles and for regular maintenance.
3.
Fences shall be maintained by the Property Owner(s) or Home Owners Association.
F.
Dry Bottom Basin: For basins designed without permanent pools:
1.
Interior Drainage: Provisions must be made to facilitate interior drainage, to include the provision of natural grades to outlet structures, longitudinal and transverse grades to perimeter drainage facilities, or the installation of subsurface drains.
2.
Multipurpose Features: These may be designed to serve secondary purposes for recreation, open space, or other types of use which will not be adversely affected by occasional or intermittent flooding.
3.
Cleaning: The basins shall be designed for periodic cleaning and removal of sediments, which shall be removed from the site or otherwise disposed of in an appropriate manner.
4.
Elimination of Standing Water: An impervious pilot channel shall be installed in the bottom of dry detention basins to assure continuous movement of stormwater through the system and avoid standing water in the basins during low volume storm events and dry periods.
G.
Wet Basins: For basins designed with permanent pools:
1.
Facilities for Emptying: For emergency purposes, cleaning, or shoreline maintenance, facilities shall be provided or plans prepared for the use of auxiliary equipment to permit emptying and drainage.
2.
Pollution Abatement: Aeration facilities may be required when the quality of the influent and detention time would result in a lowering of dissolved oxygen content in the basin.
3.
Slopes: Approach slopes shall be at least 6:1 but not more than 3:1 and shall be at least four (4) to six (6) feet wide and slope gently toward the basin. The side slopes shall be of non-erosive material with a slope of 1:1 or flatter. The ledge shall be four (4) to six (6) feet wide and slope gently toward the water. There shall be a freeboard of twelve (12) to eighteen (18) inches above the high-water elevation on all retention basins.
4.
Cleaning: The basins shall be designed to include sediment traps in all inlets. Sediment traps shall be designed to permit periodic cleaning and maintenance. A basin maintenance plan shall be developed to insure that the design depths of the basin will remain over time.
H.
Building Regulations:
1.
Rooftop Storage: Detention storage requirements may be met either in total or in part by detention on flat roofs. Design specifications of such detention shall be a part of the application for a zoning certificate. These specifications shall include the depth and volume of storage, design of outlet devices and down drains, elevations of overflow scuppers, design loadings for the roof structure, and emergency overflow provisions. Rooftop storage shall not be permitted to drain directly into sanitary sewers or streets.
2.
Parking Lot Storage: Paved parking lots may be designed to provide temporary detention storage of stormwater on a portion of their surfaces not to exceed twenty-five (25) percent. Outlets shall be designed to empty the stored waters slowly, and depths of storage must be limited so as to prevent damage to parked vehicles. Storage areas shall be posted with warning signs and shall be designed to fill to maximum depth in not less than two (2) hours.
3.
Detention Storage: All or a portion of the detention storage may also be provided in underground detention facilities.
I.
Retention in floodplains shall be permitted only in depressed floodplain areas: Retention shall not be permitted in riverine floodplains.
8.10.06 Maintenance of facilities: The developer or site owner shall be responsible for the maintenance of all improvements. Thereafter, all detention improvements shall be maintained in perpetuity and cannot be developed for any other use which would limit or cause to limit the use for detention.
8.10.07 Inspection of facilities: The developer's or owner's engineer shall be required to inspect all drainage facilities under construction and certify their compliance with approved plans. In addition, a registered engineer, employed by the City of Santa Fe, may inspect all drainage facilities while under construction. When facilities are not constructed according to approved plans, the City has the explicit authority to compel compliance and require correction of any situations which are not according to approved plans.
8.10.08 Drainage and Detention Administration:
A.
Definitions
1.
Small Project Development: for purposes of this section, is defined as:
[All Single Family Residential Subdivisions.]
a.
A subdivision of land that meets the definition of Minor Plat as defined by the Santa Fe Subdivision Development Ordinance and is zoned as R-1 Single Family Residential or is zoned as AR Agricultural Residential use, or,
[All Single Family Construction.]
b.
Development of a single parcel of land zoned as R-1 Single Family Residential or zoned as AR Agricultural Residential use, and not approved under a Conditional Use or Planned Unit Development, or,
[All Commercial Subdivisions.]
c.
All Non-Single Family Subdivisions. A subdivision of land that meets the definition of Minor Plat as defined by the Santa Fe Subdivision Development Ordinance for commercial, industrial or multi-family residential purposes and,
i.
Is located on a tract of land or lot of less than one (1) acre prior to such subdivision/development, and,
ii.
The primary building is of less than five thousand (5,000) square feet in area and,
iii.
Wherein the aggregate area of all buildings on the site will be less than ten thousand (10,000) square feet in area, for the original tract, and,
iv.
Wherein the aggregate area of all impervious surfaces on the entire original tract will not exceed twenty eight thousand (28,000) square feet or,
[All Commercial Construction.]
d.
Development of a parcel of land, existing at the time of passage of this regulation, for commercial or industrial purposes and,
i.
Is located on a tract or lot of less than one (1) acre and,
ii.
The primary building will be less than five thousand (5,000) square feet or less in area and,
iii.
Wherein the aggregate area of all buildings will be less than ten thousand (10,000) square feet in area and,
iv.
Wherein the aggregate area of all impervious surfaces on the site will not exceed twenty eight thousand (28,000) square feet.
2.
Large Project Development. Large Project Development shall be all other development not classified as Small Project Development.
3.
Aggregate Area of All Impervious Surfaces defined: the aggregate area of all impervious surfaces of a development or construction project is the total gross impervious weather surface area of all facets of the site projected vertically to the mean grade and includes but is not limited to building roofs, battered walls, parking lots, sidewalks, hard landscaping features, stabilized soils, compacted soils, improved lay down yards, improved storage yards and similar surfaces.
4.
Continued development of tracts and subdivision of lands: Continued development of tracts and subdivision of lands that result in conditions exceeding any of the criteria of this section (8.10.08) shall require the design and construction of storm water detention for all increased flows resulting from such continued development.
5.
Single-Family Residential Construction: Construction of a single-family residential structure on a single tract of land, in any zoning district other than R-1 —Single Family and AR —Agricultural Residential, incompliance with the Zoning Matrix shall be considered Small Project Development for that portion of the site devoted to the single-family use.
B.
Drainage and Detention Required: Drainage and detention of storm water shall be provided as follows:
1.
Drainage and detention of small project development shall be designed to standards established in Section 8.10.08.D Small Development Standards .
2.
Large project development shall be designed and constructed to conform to the provisions of this Article for detention of stormwater.
3.
Detention and drainage improvements shall be designed to the standards of the Dickinson Bayou Watershed Drainage Criteria Manual for Galveston County and the Texas Water Development Board and the provisions of this Article. Conflicts between the standards of the Dickinson Bayou Watershed Drainage Criteria Manual for Galveston County and the Texas Water Development Board and the provisions of this Article shall be controlled by the provisions of this Article.
4.
The developer shall be responsible for design and construction of all detention required by Single-Family and Agricultural Residential Large Project Development.
5.
Multifamily, Multi-Tenant Commercial and Multi-Tenant Industrial Development. The developer shall provide detention and stormwater management for all lots and tracts within Multifamily, Multi-Tenant Commercial and Multi-Tenant Industrial zones. It is the intention of this Section to require the design of stormwater control and detention for the entire tract when the nature of the separate uses are known. Design and construction of the detention for individual lots, when the specific use and building configuration is not known by the developer, may be deferred until each lot is improved; however, the developer shall provide a master drainage and detention plan that makes provision for all future detention and drainage for the site; furthermore, the developer shall bind all future development to the criteria established by the master drainage and detention plan.
6.
Detention shall not be required when subdivision is created by a court of law or when property is subdivided for agricultural purposes into five (5) acre and larger tracts.
C.
City/District Jurisdiction: All development and subdivision of land shall be submitted by the developer to Galveston County Drainage District #1 for review, comment and jurisdictional determination. The District shall determine whether the proposed development falls within District jurisdiction or shall determine that the District has no interest in the development's storm water design and construction oversight. The City shall issue building permits for proposed development that is designed to conform to the provisions of this Article for detention of storm water."
D.
Small Development Standards: Sheet flow shall be limited to the first 150' from the right-of-way line of adjoining streets. Parking lots and other impervious surfaces beyond 150' shall have underground internal drainage structures. Internal drainage shall be conducted to buried storm sewers or to open collector ditches.
(Ord. No. 10-2004, 5-27-04; Ord. No. 29-2007, § 1, 12-13-07; Ord. No. 12-2008, §§ 1—4, 7-24-08)
Note— Ord. No. 12-2008, adopted July 24, 2008 provides that failure to comply with any portion the ordinance (sections 8.10.04, 8.10.08B, and 8.10.08C) shall be deemed a misdemeanor, and the violator shall be liable for a fine of not less than $2,000.00, and each day such violation continues shall constitute a separate offense.