(A) It is the objective of this subchapter to control soil erosion and sedimentation resulting from development activities covering one or more acre(s). While measures must be taken to control and guarantee that post-development stormwater runoff from any development must not exceed that of pre- development, additional measures must be taken to control erosion and sedimentation ensuring that sediment is not transported from the site by a storm event of 10-year frequency or less.
(B) The following principles shall apply to all development activities covered by this subchapter and to the preparation of the submissions required under § 156.16.
(1) Preserving and protecting the natural topography. Site development should be planned so that it is consistent with and conforms to the topography and soils of the site so as to minimize and prevent soil erosion.
(2) Protection of adjacent properties. Properties adjacent to the site of a land-disturbing activity shall be protected from sedimentation by preserving a permanent vegetation buffer strip around the lower perimeter of the activity or by installing perimeter controls such as sediment barriers, filters, straw bail dikes or sediment basins or by a combination of such measures. Vegetative buffer strips should be at least 10 feet in width and may be used alone only where runoff in sheet flow is expected according to the Erosion and Sedimentation Control Plan. If at any time it is determined by the agent that a vegetated buffer strip alone is ineffective in preventing sediment movement on to adjacent property, additional perimeter controls must be provided.
(3) Cut and fill slope. Development shall reflect the topography and soils of the site so as to create the least potential for erosion. Areas of steep slopes where high cuts and fills may be required shall be avoided whenever possible, and natural contours shall be followed as closely as possible. In the design of cut and fill slopes, consideration must be given to the length and steepness of the slope, the soil type, upslope drainage area, groundwater conditions and other applicable factors. Depending on the circumstances, acceptable design options may include:
(a) The use of permanent vegetation alone with special anchoring such as netting to hold mulch on newly seeded areas. When seeding and mulching, special care must be given to ensure land is properly fertilized, seeded, mulched, anchored and watered. Newly seeded areas shall be watered gently and regularly as necessary to keep the soil sufficiently moist. Grass shall be watered as needed until grass is at least two inches tall.
(b) The use of special structural materials such as riprap, gabions, revetments, retaining walls or other methods sufficient to prevent excessive erosion.
(4) Vegetation. Natural vegetation shall be retained and protected whenever possible. If vegetation is the developer's choice, a permanent vegetative cover shall be established on denuded areas not otherwise permanently stabilized. Permanent vegetation and related structures shall be installed as soon as practical or within the time specified in the site preparation permit. Permanent vegetation shall not be considered established until a ground cover is achieved which, in the opinion of the agent, is mature enough to control soil erosion satisfactorily and to survive severe weather conditions.
(5) Channel stability in both natural and man-made waterways. A Texas-registered engineer must design new ditches for adequate stability and capacity. In addition, if existing natural drainage channels will be used to convey increased volumes of stormwater from a site, the engineer may need to provide reinforcement measures. All erosion control plans will detail how to protect the ditches and/or natural drainage from excessive erosion and sedimentation.
(6) Timing and stabilization of sediment- trapping measures. Sediment basins and traps, perimeter dikes, sediment barriers and other measures intended to trap sediment on-site must be constructed as a first step in grading and must be made functional before upslope land-disturbing activity takes place. Soil stabilization of earthen structures such as dams, dikes and diversions must occur within 15 days of installation of the structure.
(7) Stabilization of waterways and outlets. All on-site stormwater conveyance channels shall be designed and constructed to withstand the expected velocity of flow from a 10-year frequency storm without erosion. Stabilization adequate to prevent erosion must also be provided at the outlets of all pipes and paved channels.
(8) Construction on slopes or adjacent to water bodies or courses. For channel or slope construction on slopes greater than 3:1, back-up protection for the primary erosion control measure should be provided. Any new development adjacent to an existing ditch should have a minimum of 15-foot drainage access casements on each side of the ditch. In addition, no property owner may install a fence within 15 feet of a ditch, stream, brook or other natural drainage channel; except where a concrete flume or concrete channel is constructed, the abutting property owner is allowed to construct a fence up to the edge of the concrete. However, the city reserves the right to remove the fence in order to access the drainage structure for needed maintenance.
(9) Stormwater management criteria for off- site erosion. Provision shall be made to accommodate the increased runoff caused by changed soil and surface conditions during and after development. Drainageways shall be designed so that the final gradients and the resultant velocities of discharges will not create additional erosion.
(10) Aesthetics. In the design of erosion control facilities and practices, aesthetics and the requirements of continuing maintenance shall be considered.
(Ord. 2002-31, passed 11-12-02; Am.Ord.2005-29, passed 9-13-05)