ARTICLE 28.10 ENVIRONMENTAL AND IMPERVIOUS COVER REGULATIONS

With the preliminary plan submittal, and before a subdivision plat or site development plan can be approved, an environmental assessment shall be prepared by an environmental specialist, as defined in section 22.02.001.

If a site development plan is being submitted for a lot that is part of a plat that has already had an approved environmental assessment conducted for it, the site development plan shall be submitted with a copy of the previously approved environmental assessment. If the assessment does not provide specific information for the site in question or does not take into account recent land uses or changes to the property, the code official or city engineer may require additional information.

Unless the code official or city engineer determines that, due to the scope and nature of the proposed development, some of the information is unnecessary, the environmental assessment shall include information on the following subjects:

Existing land use.

Previous land uses.

Vegetation.

Topography and surface water.

Geology.

Soils.

(7)

Water wells, cisterns, septic systems, buried fuel tanks, etc.

(8)

Critical environmental features, as defined in section 28.10.004.

The environmental assessment shall be accompanied by a letter from the project engineer which shall include the following items:

An explanation of how the design of the subdivision plat or site development plan has been accomplished to preserve to the greatest extent reasonable any significant trees and vegetation on the site and to provide maximum erosion control and overland flow benefits from such vegetation.

An explanation of how proposed drainage patterns of the proposed subdivision plat or site development plan shall protect the quality and quantity of recharge at significant point recharge features, if applicable.

Proposed means of protecting identified critical environmental features, if applicable.

Environmental justification for spoil disposal locations or roadway alignments.

§ 28.10.004 Critical environmental feature buffer zone.

A description of any industrial uses proposed, as well as a program for pollution abatement, if applicable.

(e)

An environmental assessment dated five (5) or more years prior to the plan submittal date to the city shall be accompanied by an update letter from an environmental specialist.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

Definition of critical environmental features.

Critical environmental features are features that have been identified by the environmental assessment and/or by the city to be of critical importance to the protection of one or more environmental resources. They include, but are not limited to, such features as bluffs, springs, canyon rimrocks, caves, sinkholes and wetlands.

Establishment of zone.

A critical environmental buffer zone shall be established 50 feet from identified critical environmental features. This buffer zone shall be shown on all preliminary plans, final plats, and construction plans.

Construction prohibited.

No clearing, alteration, or construction other than for parks or hiking trails approved by the city shall be undertaken in the critical environmental feature buffer zone. The natural vegetative cover shall be retained in this buffer zone to the maximum practical extent.

Drainage.

Drainage patterns shall be designed to protect critical environmental features from runoff from developed areas or to maintain the catchment areas of recharge features in a natural state. Special erosion controls shall be utilized where necessary to avoid impacts of erosion or sedimentation.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

§ 28.10.005 Buffer zones.

Definition of buffer zone.

Buffer zones protect waterways and aquatic resources from the short- and long-term impacts of development activities. Buffer zones shall remain free of construction, development, or other alterations except for utility and roadway crossings. The number of crossings through buffer zones should be minimized. No stormwater treatment facilities, golf courses, or wastewater irrigation shall be located in the buffer zone. Stormwater discharge from the development shall be dispersed into overland patterns before reaching the buffer zone.

Buffer zones are located on creeks or swales that have more than five (5) acres of contributing drainage area. To protect the creek buffer, stormwater discharged from water quality basins must enter the buffer in a sheet flow manner. Bypass flows from storms in excess of the basin design storm must be conveyed in a stable manner through the buffer zone to the receiving water body. This can be accomplished through application of level spreader systems. Some limited vegetation management is allowed within the buffer zone to enhance the character of the buffer; however, this effort must be approved by the city before commencement.

A creek shall be defined as a distinct channel that can convey running water. This definition will be used to determine the beginning or uppermost headwater of the creek to initiate the application of the buffer zones.

Buffer zones.

Option 1: Drainage area buffer zone.

Creeks/swales draining less than 40 acres but more than five (5) acres, excluding roadside swales, shall have a minimum buffer width of 25 feet from the centerline of the creek/swale.

Creeks/swales draining less than 128 acres but more than 40 acres shall have a minimum buffer width of 50 feet from the centerline of the creek/swale.

(C)

Creeks/swales draining less than 320 acres but more than 128 acres shall have a minimum buffer width of 100 feet from the centerline of the creek/swale.

(D)

Creeks/swales draining less than 640 acres but more than 320 acres shall have a minimum buffer width of 200 feet from the centerline of the creek/swale.

(E)

Creeks/swales draining 640 acres or greater shall have a minimum buffer width of 300 feet from the centerline of the creek/swale.

Option 2: Floodplain buffer zone.

For creeks or rivers draining less than 40 square miles but more than five (5) acres, the buffer zone shall extend a minimum of 25 feet from the 100-year floodplain boundary paralleling each side of the creek or swale. The 100-year floodplain shall be based on the fully developed conditions as approved by the city.

For creeks or rivers draining more than 40 square miles, the buffer zone shall be considered equal to the 100-year floodplain as designated by Federal Emergency Management Agency or by an engineered floodplain study approved by the city.

Lake Travis.

For Lake Travis, the zone shall be that area below the current FEMA 100-year floodplain level.

Buffer zone technical requirements.

The delineation of the buffer zone shall be shown on all plan sets, including clearing, grading, and construction plans. It is recognized that there are some necessary impacts to the buffer. The following disturbances may be allowed in the buffer zone with approval from the city and with efforts made to minimize these impacts.

Roadway crossings.

Road crossings of creeks should be minimized. Grading, including cut and fill, should be reduced to a minimum. Open sections and swales should be used and concentration of flows into large pipes or outlet structures should be minimized. Where possible, sheet flow shall be directed to buffer zones in order to take advantage of the pollutant filtering potential of the buffer. The roadway design should consider long-term channel and bank stability and habitat and use appropriate techniques to manage anticipated long-term channel adjustments. Vegetation and/or soil protection blankets are to be installed immediately after embankment compaction to prevent soil discharges. Roadway crossings can be optimized to serve as stormwater detention structures when culverts are sized to manage peak flow rates and the flood storage pool remains undisturbed. Limited clearing of vegetation via hand methods may be allowed and requires approval before activity commencement.

Stormwater detention structures.

Stormwater detention is allowed within the buffer zone when the detention embankment/structure occupies a narrow footprint similar to utility and roadway crossings and no excavation takes place within the flood storage pool. Limited clearing of vegetation via hand methods may be allowed and requires approval before activity commencement. Vertical rock or concrete wall structures can provide floodwater storage with a small disturbance area and serve as the embankment.

Utility crossings.

Grade controls and bank stabilization should be placed at all crossings of drainageways. For those utilities that do not require continual access, replacement and revegetation with in-kind native plants is recommended. Utility crossings should occur at or near right angles to the maximum extent practical. The utility design should consider long-term channel and bank stability and use appropriate techniques to manage anticipated long-term channel adjustments.

Low impact park development.

Development within the buffer zone should be limited to trails, picnic facilities, and similar construction that do not significantly alter the existing vegetation or drainage patterns. Trail width should be minimized and the use of gravel, mulch, or other alternate paving surfaces should be considered if all accessibility and emergency vehicle needs are met. Trails should be graded so that they do not concentrate flows and adequate outfall protection should be provided at crossings of minor drainageways. Trails should include areas for pet waste management and adequate signage to encourage cleanup of any pet wastes. Pedestrian bridges should be considered at major crossings, rather than culverts.

Storm drainage outfalls.

Direct connection of shallow concentrated flow, open channel flow and storm drain pipes to the stream channel through the buffer shall be avoided. Energy dissipation devices, such as on-contour level spreaders, infiltration trenches, vegetated filter strips, rock trenches, inverted weirs or other permanent BMP’s shall be placed outside of the buffer to produce sheet flow. After the stormwater energy is diffused before entering the buffer, the resultant runoff should enter the receiving channel at nonerosive velocities as shallow concentrated flow. Rock rip-rap of sufficient size should be placed downstream of the storm drain outfalls to manage scour and protect the outfall structure.

§ 28.10.006 Residential construction within the Lake Travis buffer zone.

Level spreaders.

A level spreader typically is an outlet designed to convert concentrated runoff to sheet flow and disperse/dissipate its energy uniformly across a slope to prevent erosion.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

General standards.

All new construction and improvement of any existing structure within the Lake Travis buffer zone shall be performed so as to keep the structure reasonably safe from flooding, and in accordance with all applicable regulations as well as with the following standards:

All improvements shall be designed or so modified so as to be adequately anchored to prevent flotation, collapse, or lateral movement of the structure in the presence of floodwaters.

All improvements shall be constructed by methods and practices so as to minimize flood damage.

All improvements shall be constructed with materials and equipment resistant to flood damage.

All electrical, heating, ventilation, plumbing, and air-conditioning equipment and other service facilities shall be designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

All water supply systems, including new and replacement water supply systems, shall be designed to prevent or eliminate infiltration of floodwaters into the system.

All sanitary sewer systems, including new and replacement sanitary sewer systems, shall be designed to prevent or eliminate infiltration of floodwaters into the structure’s systems and discharge of sewage into floodwaters.

(7)

All on-site disposal systems, including but not limited to septic tank systems located on the site of the structure, shall be located so as to prevent impairment of the function of those systems in the presence of floodwaters and to prevent contamination of floodwaters from those systems during flooding.

(8)

Adequate drainage must be provided to reduce exposure to flood hazards, including adequate paths around structures on slopes to guide floodwaters around and away from proposed structures.

(9)

Fully enclosed areas below the lowest floor that are used solely for parking, building access, or storage in an area other than a basement and that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a registered architect or professional engineer licensed in the state, or must meet or exceed the following minimum criterion: include a minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding, with the top of all such openings no higher than one foot above grade or BFE, whichever is lower. Openings may be equipped with screens, louvers, valves, or other coverings or devices, provided that they permit the automatic entry and exit of floodwaters.

(10)

No rise of BFE in the floodplain: No new construction, substantial improvements, or other development (including cut and/or fill) shall be permitted within the Lake Travis buffer zone unless:

It is first demonstrated by engineering data submitted by the applicant’s engineer in accordance with the various requirements and procedures set forth in this order that the cumulative effect of the proposed development will not increase the water surface elevation of the base flood:

(i)

On adjacent properties;

(ii)

At any point within the city; or

(iii)

Immediately adjacent to neighboring communities; and

A conditional letter of map revision (CLOMR) has been approved by FEMA. A letter of map revision (LOMR) must also be obtained by the applicant upon completion of the proposed encroachment;

(11)

Compensatory storage: Whenever any portion of a floodplain is authorized for use, the space occupied by the authorized fill or structure below the base flood elevation shall be compensated for and balanced by a hydraulically equivalent volume of excavation taken from below the base flood elevation. All such excavations shall be constructed to drain freely to the watercourse. Any general alteration or development of the floodplain using this method requires a FEMA approved letter of map change (LOMC).

(12)

New development or substantial improvement in the 100-year floodplain may not increase erosive water velocity onsite or offsite, and

(13)

New development or substantial improvement in the 100-year floodplain will require an LOMC for any development that alters the floodplain.

Base flood elevation requirements in the Lake Travis buffer zone.

All new construction and additions to and substantial improvement of any residential structure within the Lake Travis buffer zone shall have the lowest floor, including basement, and all utilities elevated above at least one foot above the base flood elevation.

Nonconforming uses.

A structure, or the use of a structure or premises, which was lawful before the adoption of this section, but which does not conform to the requirements set forth herein, may be continued subject to the follow conditions.

No such use shall be expanded, changed, enlarged, or altered in a way which increases its nonconformity.

No substantial improvement to the structure shall be made unless the structure is changed to conform to these regulations.

(C)

If a nonconforming use is discontinued for a period of 90 days or more, any future use of the building or premises shall conform to these regulations.

(D)

Any nonconforming use or structure which is destroyed by any means, including floods, or which has sustained substantial damage shall not be reconstructed except in conformance with the provisions of these regulations.

The following procedures shall be used to determine whether a structure or use of a structure has sustained substantial damage pursuant to this section.

The owner shall obtain an estimate of fair market value for the structure which has been damaged.

The owner shall obtain an estimate for the cost of repairs to the damaged structure. Acceptable estimates can be obtained from the following sources:

(i)

Itemized estimate (as to both materials and labor) made by licensed contractors or other professional estimators in the construction industry; and

(ii)

For insured structures damaged by floods, the monetary damage estimated by the National Flood Insurance Program claims adjuster (structure only, not contents).

(C)

The owner shall provide an estimate for the cost of repairs or improvements which have been made to the structure since March 28, 1995.

(D)

The owner shall submit a completed application form along with the requested cost and appraised value figures to the city.

Upon receipt of the information outlined in subsection (c)(2), the floodplain administrator shall verify the accuracy of the information and determine if the structure has been, or will be, substantially improved as a result of the repair work or other improvements which have been or need to be made. If the value of repairs or improvements does not constitute a substantial improvement as defined in this chapter and does not exceed 50% of the market value of the structure, then a permit will be issued by the floodplain administrator to begin the repairs. If the value of repairs or improvements exceeds 50% of the market value of the structure or constitutes a substantial improvement, then a permit will be denied unless the structure is to be reconstructed outside of the floodplain or constructed in accordance with the standards set forth in this chapter for new developments and substantial improvements.

(Ordinance 2011-09-19-01 adopted 9/19/11)

§ 28.10.007 Uplands zone.

Definition.

The uplands zone shall consist of all lands and waters that are not included within the critical environmental feature buffer zone or a buffer zone.

Impervious cover allowed.

The maximum allowable impervious cover for single-family or duplex development shall be 50% of the net site area.

The maximum allowable impervious cover for all other development shall be 60% of the net site area.

§ 28.10.008 Transfer of impervious cover credit.

For development within the extraterritorial jurisdiction, the maximum allowable impervious cover shall be 35% of the net site area.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11; Ordinance 2023-10-16-03 adopted 10/16/2023)

Impervious cover credit may be transferred only between lots within the same preliminary plan.

§ 28.10.009 Building sites and calculations of impervious cover.

An applicant transferring development intensity must note the transfer on the plats of both the transferring and receiving tracts, in a manner satisfactory to the zoning and planning commission, and must file in the deed records a restrictive covenant, approved by the city attorney, that runs with the transferring tract

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

All lots or tracts of land shall contain an adequate building site prior to development. The 100-year floodplain shall remain free of construction, development, or other alterations except for utility crossings, roadway crossings, and other at-grade improvements (such as walkways) as approved by the city.

Single-family or duplex development: Impervious cover calculations shall include actual calculations for street sections, any other proposed impervious cover, and the total of an assumed impervious cover for each proposed lot. Impervious cover assumptions per lot shall be based on the following:

Lot Size (ft²)	7,499 and less	7,500–9,999	10,000–14,999	15,000 and greater
I.C. Assumption per Lot	3,000 ft²	4,000 ft²	6,000 ft²	7,000 ft²

Site development: Impervious cover calculations shall be actual calculations based on the proposed plans.

§ 28.10.010 Calculation of net site area.

All impervious surfaces (building footprints, paved surfaces, sidewalks, decks/patios, dumpster pads, A/C pads, mail kiosk pad, etc.) shall be included in the calculations and charged against impervious cover allowances. Roads, parking areas, buildings, and other construction are to be assumed as 100 percent impermeable unless specific proposed alternate surfaces are authorized as being less than such by the city engineer. Water quality basins, detention ponds, earthen swales, and any naturally impermeable features, such as rock outcrops need not be calculated as impervious cover.

(e)

All pedestrian sidewalks within street rights-of-way or parallel to private streets may be excluded from the impervious cover calculations.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

Excluded from net site area.

Land in critical environmental feature buffer zones and the buffer zone.

Land on slopes greater than 35 percent.

Included in net site area.

One hundred (100) percent of all acreage on 0–15% slopes in the uplands zone.

Forty (40) percent of all acreage on 15–25% slopes in the uplands zone.

§ 28.10.011 Municipal separate storm sewer system (MS4).

Twenty (20) percent of all acreage on 25–35% slopes in the uplands zone.

(Ordinance 2011-05-16-05, rev. 2, adopted 5/16/11)

Conveyance.

Stream, channel, drainageway, drainage/dry well, intermittent stream, ephemeral stream, floodplain, karst feature, storm drainage system, drainage system appurtenance, waterbody, watercourse or waterway.

Discharge.

Any direct or indirect addition including dumping, spilling, leaking, pumping, pouring, emitting, emptying, leaching, disposing or otherwise introducing any pollutant, stormwater, or any other substance whatsoever into the municipal separate storm sewer system (MS4) or conveyance.

Hazardous material.

Any material, including any substance, waste, or combination thereof, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may cause, or significantly contribute to, a substantial present or potential hazard to human health, safety, property, or the environment when improperly treated, stored, transported, disposed of, or otherwise managed.

Illicit connections.

Any drain or conveyance, whether on the surface or subsurface that allows an illegal discharge to enter the storm drain system or a conveyance, including but not limited to any conveyances that allow nonstormwater discharge including sewage, process wastewater, and washwater to enter the storm drain system and any connections to the storm drain system from indoor drains and sinks.

Municipal separate storm sewer system (MS4).

The stormwater drainage system operated and maintained by the city which is comprised of the following: The system of conveyances (including roads with drainage systems, municipal streets, catchbasins, curbs, gutters, ditches, manmade channels, or storm drains) owned and operated by the city and designed or used for collecting or conveying stormwater, and which is not used for collecting or conveying sewage.

Nonstormwater discharge.

Any discharge into the municipal separate storm sewer system (MS4) or surface water that is not entirely composed of stormwater.

Person.

Any individual, association, organization, partnership, firm, corporation, or other entity recognized by law and acting as either the owner or as the owner's agent.

Pollutant.

Anything which causes or contributes to pollution. Pollutants may include, but are not limited to: Paints, varnishes, and solvents; oil and other automotive fluids; nonhazardous liquid and solid wastes and yard wastes; refuse, rubbish, garbage, litter, or other discarded or abandoned objects, articles, and accumulations, so that same may cause or contribute to pollution; floatables; pesticides, herbicides, and fertilizers; hazardous substances and wastes; sewage, fecal coliform and pathogens; dissolved and particulate metals; animal wastes; wastes and residues that result from constructing a building or structure; and noxious or offensive matter of any kind.

Stormwater.

Any surface flow, stormwater runoff, snow melt runoff, and surface runoff and drainage consisting entirely of water from any form of natural precipitation.

TPDES.

Texas Pollutant Discharge Elimination System; program delegated to the State of Texas by EPA pursuant to 33 USC 1342(b).

Water quality standard.

The designation of a body or segment of surface water in the state for desirable uses and the narrative and numerical criteria deemed by the state to be necessary to protect those uses, as specified in chapter 307 of title 30 of the Texas Administrative Code.

(Ordinance 2022-11-21-02 adopted 11/21/2022)

§ 28.10.012 Prohibition of illicit discharges.

General. No person within the city limits and extraterritorial jurisdiction of the city shall introduce, directly or indirectly, any discharge that is not entirely composed of stormwater into the municipal separate storm sewer system (MS4) or conveyances.

Prohibition of illicit discharges. No person shall discharge any pollutant or waters containing any pollutant into the MS4 or conveyances that violates chapter 26 of the Texas Water Code, violates federal law, or that causes or contributes to causing the city to violate a water quality standard, the city's TPDES permit, or any state-issued discharge permit for discharges from its municipal separate storm sewer system (MS4).

Allowable nonstormwater discharges.

It is an affirmative defense to any enforcement action for violation of subsection (a) of this section that the discharge was composed entirely of one or more of the following categories of discharges:

A discharge specified in writing by the city as being necessary to protect public health and safety.

A discharge authorized by a TPDES permit, waiver, or waste discharge order issued to the discharger and administered under authority of the Texas Commission on Environmental Quality or the United States Environmental Protection Agency, provided that the discharger is in full compliance with all requirements of the permit, waiver, order, and other applicable laws and regulations.

A discharge resulting from firefighting/fire suppression activities.

A discharge of fire protection water from standard municipal operations and training that does not contain oil or hazardous substances or materials that are required to be contained and treated prior to discharge, in which case treatment adequate to remove harmful quantities of pollutants must have occurred prior to discharge.

A discharge resulting from the standard municipal operations of street sweeping and street washing activities, which discharge is not contaminated with any soap, detergent, degreaser, solvent, emulsifier, dispersant, or any other harmful cleaning substance.

A discharge from water line flushing, but not including a discharge from water line disinfection by superchlorination or other means unless the total residual chlorine (TRC) has been reduced to less than one ppm (part per million) and it contains no harmful quantity of chlorine or any other chemical used in line disinfection.

(7)

A discharge from a potable water source not containing any harmful quantity of a substance or material from the cleaning or draining of a storage tank or other container.

(8)

A discharge from lawn watering or landscape irrigation provided that the discharge occurs in accordance with section 24.02.323.

(9)

A discharge from individual residential car washing.

(10)

A discharge from air conditioning condensation that is unmixed with water from a cooling tower, emissions scrubber, emissions filter, or any other source of pollutant.

(11)

Swimming pool water that has been dechlorinated so that total residual chlorine (TRC) is less than one ppm (part per million), that has a pH between the range of 6.0 and 10.5, and that contains no harmful quantity of chlorine, muriatic acid or other chemical used in the treatment or disinfection of the swimming pool water or in pool cleaning.

(12)

Stormwater runoff from a roof that is not contaminated by any runoff or discharge from an emissions scrubber or filter or any other source of pollutant.

(13)

A discharge or flow from a diverted stream flow or natural spring.

(14)

A discharge or flow from uncontaminated pumped groundwater, rising groundwater, or groundwater infiltration to storm drains.

(15)

Uncontaminated groundwater infiltration, as defined by 40 CFR 35.2005(20), to the MS4.

(16)

Uncontaminated discharge from a foundation or footing drain (excluding active groundwater dewatering systems), crawl space pump, or sump pump.

Prohibition of illicit connections to the MS4 or conveyances.

The construction of, use of, maintenance of, or continued use of a new or existing illicit connection to the MS4 or any conveyances is prohibited. This prohibition expressly includes any illicit connection made before passage of the ordinance codified in this article, regardless of whether such connection was permissible under law or practices applicable or prevailing at the time of connection.

(e)

Spill and release reporting.

Discovery, containment and cleanup procedure.

Notwithstanding other requirements of law, as soon as any discharger or operator of a facility or operation, or person responsible for emergency response for a facility or operation, has information of any known or suspected release of materials which are resulting or may result in an illicit discharge, such person shall take all necessary steps to ensure the discovery, containment, and cleanup of such discharge.

Hazardous materials spill.

In the event of discharge of hazardous materials, the discharger shall immediately notify emergency response agencies. Once the immediate threat has been properly contained, the discharger shall notify the city via its director of building and development services.

Nonhazardous materials spill.

In the event of a release of nonhazardous materials, the discharger shall notify the city, via its director of building and development services, in person or by telephone no later than the next business day. Notifications in person or by telephone shall be confirmed by written notice addressed and mailed to the director within three business days of the telephone notice.