The City of Austin Drainage Criteria Manual establishes standards for stormwater management, hydraulic design, and floodplain protection in the Austin region. It guides engineers, developers, and planners to meet regulatory requirements while safeguarding public safety and environmental quality. compliance.!!
Scope and Purpose
The City of Austin Drainage Criteria Manual delineates the boundaries of its application, specifying the geographic, functional, and procedural limits within which the manual operates. It articulates the primary objectives of establishing uniform stormwater design criteria, ensuring public safety, protecting water quality, and promoting sustainable land use. The manual serves as a comprehensive reference for engineers, planners, developers, and municipal staff, providing clear guidance on design standards, permitting processes, and compliance requirements. By integrating local hydrologic data, regulatory mandates, and best‑practice engineering principles, the manual supports consistent decision‑making across the Austin metropolitan area. Its purpose is to harmonize design practices, facilitate interagency coordination, and foster transparency in stormwater management, thereby contributing to the resilience and livability of the community.
Additional content describing the manual’s role in integrating community input, aligning with state and federal guidelines, and facilitating adaptive management strategies. It emphasizes the manual’s capacity to guide projects from conceptual design through construction and long‑term operation, ensuring compliance with environmental standards and fostering resilient infrastructure. This section also outlines the manual’s use as a reference for cost estimation, permitting, and performance monitoring. The manual also serves as a document, evolving with new research and stakeholder feedback to stay relevant!!
Regulatory Framework
The City of Austin Drainage Criteria Manual operates within a multi‑layered regulatory environment that integrates federal, state, and local statutes, regulations, and ordinances. At the federal level, the Clean Water Act (CWA) and the National Flood Insurance Program (NFIP) establish baseline requirements for stormwater discharges, permitting, and floodplain mapping. The Texas Commission on Environmental Quality (TCEQ) issues the Texas Stormwater Management Code, which mandates compliance with the Texas Water Code, the Texas Water Development Board’s guidelines, and the Texas Water Resources Code. Austin’s own Municipal Code, particularly Title 10, Chapter 10.1, codifies the city’s stormwater permitting procedures, design criteria, and enforcement mechanisms. The Manual aligns its design standards with the Texas Stormwater Management Code, the Texas Water Code, Austin Municipal Code, the NFIP floodplain maps, ensuring that all projects meet or exceed the most stringent applicable requirements. Additionally, the Manual incorporates the U.S. Army Corps of Engineers’ regulations for floodplain management, the Texas Department of Transportation’s (TxDOT) requirements for roadway drainage, and the Texas Water Development Board’s (TWDB) guidance on water quality and quantity. By synthesizing these diverse regulatory sources, the Manual provides a coherent framework that supports consistent, legally defensible stormwater design and management throughout the City of Austin. This framework facilitates inter‑agency collaboration and transparency in stormwater planning.
Design Criteria
Design criteria define stormwater volumes, and hydraulic performance. Austin’s Manual adopts the 100‑yr return period, 15‑minute design rainfall, and 2‑ft depth limit for runoff. It specifies channel slopes, pipe sizes, and infiltration rates to meet code and environmental goals and safe
Hydraulic Design Standards
Austin’s hydraulic design standards are rooted in the 2024 City Engineering Code, the Texas Water Code, and the U.S. Environmental Protection Agency’s National Flood Insurance Program. The manual mandates that all new stormwater conveyance systems be designed for a 100‑year return period with a 15‑minute design rainfall event, consistent with the Texas Department of Transportation’s 15‑minute design storm. Engineers must calculate peak discharges using the Rational Method for small catchments and the SCS‑Curve Number method for larger, mixed‑landscape developments. The allowable maximum depth of surface runoff is capped at 2 ft to protect pedestrian safety and reduce erosion. Channel slopes are prescribed to be no steeper than 1 in 20 for concrete channels and 1 in 15 for reinforced concrete lined open channels, ensuring adequate self‑cleansing velocities while preventing bank erosion. For pipe networks, the manual specifies minimum pipe diameters based on flow‑rate tables derived from the 15‑minute design storm, and requires the use of PVC or HDPE materials with a minimum wall thickness of 0.25 in for 4‑in diameter pipes. Hydraulic modeling must be performed with HEC‑RAS or equivalent software, and the model must be validated against historical flood data. The manual also incorporates the 2017 U.S. Army Corps of Engineers’ “Floodplain Management” guidelines, requiring that all new infrastructure be located at least 100 ft from the 100‑year floodplain edge, except where mitigation measures such as levees or retention basins are approved. In addition, the manual mandates that all design calculations be documented in a Design Report that includes flow‑rate tables, hydraulic curves, cross‑sectional profiles, and a summary of the design assumptions. The report must be reviewed and approved by the City’s Stormwater Engineering Office before construction can commence. Finally, the manual emphasizes the importance of incorporating green infrastructure, such as bioswales, permeable pavement, and rain gardens, to reduce peak discharges by at least 30 % in developments that exceed 10 acres of impervious surface. These standards collectively ensure that Austin’s stormwater system remains resilient, safe, and compliant with state regulations. Peer review by a licensed engineer is required
Hydraulic Modeling Practices
The City of Austin’s Hydraulic Modeling Practices section outlines the methodology for simulating stormwater flow and floodplain dynamics. Engineers must use HEC‑RAS or HEC‑FLOW, endorsed by the Texas Water Development Board, to model steady‑state unsteady‑flow conditions. Input data include topographic surveys, land‑use classifications, and rainfall‑runoff relationships derived from the SCS‑Curve Number method. The manual requires a minimum 1‑second temporal resolution for peak‑flow calculations and mandates that all model grids be no coarser than 10 m to capture fine‑scale topographic variations. Calibration is performed against historical flood records, with a tolerance of ±10 % for peak discharge and ±5 % for water‑surface elevations. Validation must include a comparison of simulated and observed hydrographs at at least two critical points. The model must incorporate the 100‑year return‑period design storm, and sensitivity analyses must be conducted for alternate rainfall scenarios. Documentation of all assumptions, boundary conditions, and calibration results is required in a Design Report, which must be reviewed by the City’s Stormwater Engineering Office before construction approval. Additionally, the manual specifies that models be updated annually or when significant land‑use changes occur, ensuring that the hydraulic representation remains current and reliable. All modeling activities must comply with the U.S. EPA’s National Flood Insurance Program guidelines and the Texas Department of Transportation’s floodplain mapping standards.All. The use of GIS layers for land cover, soil type, and drainage network integration is mandatory to support accurate runoff generation and routing.
Floodplain Management
The City of Austin’s Floodplain Management section establishes rules for protecting residents from flood hazards while permitting responsible development. It defines the 100‑year floodplain, the 500‑year floodplain, and the 100‑year floodplain with a 10‑foot elevation buffer, all based on the latest USGS floodplain maps. Developers must submit a Floodplain Analysis Report (FAR) that demonstrates compliance with the 100‑year floodplain criteria, including a hydraulic model, a flood‑plain map, and a mitigation statement. New construction in the 100‑year floodplain must be elevated at least 2 ft above the Base Flood Elevation (BFE), or a flood‑proofing strategy must be employed. Projects in the 500‑year floodplain require a 1 ft elevation above BFE and a storm‑water retention system that captures at least 30 % of the design storm. The manual requires preservation of existing flood‑plain vegetation and clear drainage pathways. The City’s Floodplain Management Office reviews all submissions; non‑compliant projects are returned for revision. Developers must provide floodplain education materials to residents. The manual follows the Texas Floodplain Management Act and the National Flood Insurance Program, ensuring compliance with federal and state standards. All floodplain activities are documented in a Floodplain Management Plan (FMP), reviewed and approved by the City’s Stormwater Engineering Office before permits are issued. The FMP includes inspection schedules and contingency plans for extreme events. A monitoring plan is required for projects that alter existing drainage patterns. The plan must be reviewed annually. The manual is updated annually to reflect hydrologic data, climate projections, and regulatory changes. By following these standards, Austin ensures a safe, resilient, environmentally responsible growth path for its residents. All projects must comply.!
Stormwater Management Practices
The City of Austin’s Stormwater Management Practices section outlines the design, implementation, and maintenance requirements for stormwater systems within the jurisdiction. It mandates that all new developments incorporate Low‑Impact Development (LID) techniques, such as rain gardens, bioswales, permeable pavement, and green roofs, to reduce runoff volume and velocity. The manual specifies that stormwater retention and detention basins must be sized to capture at least 30 % of the design storm for sites exceeding 10 acres, and that infiltration trenches be used for smaller sites. It requires that all stormwater infrastructure be constructed in accordance with the Texas Department of Transportation (TxDOT) and the American Society of Civil Engineers (ASCE) standards, and that the design storm be based on a 10‑year return period for residential projects and a 100‑year return period for commercial projects. The manual also prescribes that developers provide a Stormwater Management Plan (SMP) that details the location, capacity, and maintenance schedule of each LID feature. The SMP must be reviewed and approved by the City’s Stormwater Engineering Office before issuance of a permit. All stormwater systems must be inspected annually, with corrective actions documented in a Maintenance Log. The manual encourages the use of real‑time monitoring sensors to track system performance and to facilitate adaptive management. By integrating these practices, Austin aims to reduce peak flows, improve water quality, and enhance ecological resilience across the watershed. Additionally, the manual requires that stormwater facilities be designed to accommodate projected increases in precipitation intensity due to climate change, incorporating a 10 % design storm adjustment factor. It also mandates that all new construction include a stormwater fee based on impervious surface area, with revenues directed to the Austin Water Conservation Fund. The manual provides guidelines for retrofitting existing infrastructure, encouraging the replacement of outdated detention basins with modern, modular systems that allow for future scalability. Finally, the manual emphasizes community outreach, requiring developers to provide educational materials to residents about the benefits of LID and the importance of maintaining green infrastructure. Compliance with these standards is enforced through periodic audits and penalties for non‑compliance.
Green Infrastructure Requirements
The City of Austin’s Green Infrastructure Requirements mandate that all new developments integrate a minimum of 30 % of the site’s impervious area with permeable or vegetated surfaces. Design standards specify that rain gardens, bioswales, and infiltration trenches must be sized to capture at least 25 % of the design storm runoff; Green roofs are required on buildings exceeding 5 000 sq ft of roof area, with a minimum 3‑year lifespan and a 1.5 in per year rainfall capture rate. Developers must submit a Green Infrastructure Plan (GIP) that details the location, dimensions, and maintenance schedule for each feature, and the plan must be reviewed by the City’s Stormwater Engineering Office before issuance of a permit. All green infrastructure assets are subject to annual inspections, with corrective actions documented in a Maintenance Log. The manual encourages the use of real‑time monitoring sensors to track infiltration rates and system performance, and requires that data be reported quarterly to the City’s Water Management Portal. In addition, the City requires that developers contribute to a Green Infrastructure Fund, calculated as $0.50 per square foot of new impervious surface, to support ongoing maintenance and community outreach programs. Compliance with these requirements is enforced through periodic audits, and non‑compliance results in penalties or revocation of permits. these standards, Austin aims to reduce peak flows, improve water quality!? These practices meet water and standards
Construction Standards
All construction activities must comply with the City’s Drainage Criteria Manual, prescribing detailed procedures for site preparation, erosion and sediment control, and stormwater conveyance installation. to ensure compliance with state and federal regulations. Prior to excavation, a site preparation plan must be submitted, detailing grading slopes, compaction schedules. to mitigate erosion risks. Excavated material must be stockpiled, with slopes not exceeding 2:1 and covered with erosion control blankets or geotextile mats. ensuring adequate infiltration. During construction, all stormwater pipes and channels must be installed, with pipe joints sealed using approved sealants and inspected for leaks before backfilling. Ensuring no surface runoff. Backfill material must be layered in 6‑inch increments, compacted to 95 % of the dry density, and tested with a Proctor test. Construction crews must maintain a log of activities, including weather, material deliveries, and deviations from the approved plan. The manual mandates that construction sites implement a stormwater management plan including sediment basins, silt fences, and temporary detention ponds, with maintenance schedules documented. Upon completion, a final inspection must verify all erosion control measures are in place, and a compliance certificate must be submitted to the City’s Stormwater Office. Failure to meet these standards can result in fines, stoppage, revocation permits
Maintenance and Inspection
Regular monitoring of drainage infrastructure is required to preserve system integrity and comply with the City of Austin Drainage Criteria Manual. A scheduled inspection program must be established, with inspections conducted at least quarterly for new developments and annually for existing projects. Each inspection should document pipe conditions, outlet functionality, sediment accumulation, and erosion control effectiveness. Inspectors must use calibrated flow meters, pressure gauges, and visual assessment tools to verify that discharge rates match design specifications. Any deviations exceeding 10 % of the design flow must be reported immediately and corrective action must be initiated within 30 days. Maintenance activities include cleaning debris from catch basins, repairing cracked or damaged pipe joints, and restoring vegetation on riparian buffers. All maintenance records must be logged in a centralized database, with timestamps, personnel signatures, and photographic evidence. The manual requires that any significant repairs or replacements be approved by the City’s Stormwater Engineering Department before work begins. Additionally, the manual mandates that stormwater detention structures be inspected for structural integrity, water level control, and spillway functionality. Failure to perform these inspections or to document findings can result in penalties, including suspension of permits and mandatory remediation orders. The City encourages the use of technology such as remote sensors and GIS mapping to enhance data collection and streamline reporting. By adhering to these maintenance and inspection protocols, developers and property owners help ensure that the drainage system remains resilient, safe, and environmentally compliant throughout its lifecycle. Periodic audits by the City’s Environmental Services will verify compliance and recommend improvements. All documentation must be retained for a minimum of five years?!!
Compliance and Enforcement
Compliance with the City of Austin Drainage Criteria Manual is enforced through permit conditions and inspections. Developers affirm adherence to design, construction, and maintenance requirements. The City’s Stormwater Management Office reviews pre‑construction and post‑construction work to verify hydraulic performance, slope stability, and environmental protection. If a facility fails to meet design capacity or shows structural deficiencies, the City issues a Notice of Non‑Compliance, requiring corrective action within a prescribed timeframe. Failure to remedy deficiencies may result in penalties, suspension of permits, or remediation orders. The manual establishes a tiered enforcement framework: minor violations trigger fines and corrective work orders, while major violations may lead to litigation and project redesign. The City maintains a public database of enforcement actions, including violation details, corrective measures, and outcomes, promoting transparency and accountability. The manual requires that any alterations to existing drainage infrastructure be reviewed and approved by the Engineering Department to prevent downstream impacts. Property owners must keep records of inspections, maintenance, and compliance reports, available to the City upon request. By integrating proactive monitoring with clear enforcement protocols, the City of Austin ensures that drainage infrastructure remains reliable, safe, and compliant with evolving regulatory standards. All drainage projects must include a monitoring plan outlining inspection intervals, data collection methods, and reporting protocols. Submitting this plan within 60 days of permit issuance is mandatory; failure triggers a compliance review. The City promotes real‑time sensors and GIS mapping to improve data accuracy and support timely decision‑making. Property owners are required to conduct annual sediment removal and ensure outlets remain unobstructed!!! This section is critical compliance.!!
City of Austin’s Drainage Criteria Manual prioritizes sustainability through integrated water resource management, green infrastructure, and climate resilience. The manual mandates that all new developments incorporate low‑impact development (LID) practices, such as permeable pavements, bioswales, and rain gardens, to reduce runoff volume and improve water quality. It also requires the use of stormwater harvesting systems to capture and reuse runoff for irrigation and groundwater recharge, thereby decreasing potable water demand. The manual aligns with the city’s Climate Action Plan by setting performance thresholds for greenhouse gas emissions associated with stormwater infrastructure projects, encouraging the use of renewable energy sources for pumping stations and treatment facilities. In addition, manual promotes the restoration of natural wetlands and riparian buffers within the watershed, which serve as carbon sinks and enhance biodiversity. The manual’s design criteria incorporate adaptive management principles, allowing for periodic reassessment of hydraulic performance under changing land‑use and climate projections. Compliance with the manual’s sustainability provisions is monitored through a mandatory reporting framework that tracks metrics such as runoff reduction, water quality improvements, and energy consumption. By embedding these goals into the regulatory fabric, the manual ensures that Austin’s stormwater systems not only protect public safety but also contribute to broader environmental and social objectives.
References
- City of Austin. (2024). Drainage Criteria Manual, 3rd Edition. Austin, TX: City of Austin.
- Texas Water Development Board. (2023). Texas Stormwater Management Guidelines. Austin, TX: TWDB.
- Environmental Protection Agency. (2022). Low Impact Development (LID) Best Management Practices. Washington, DC: EPA.
- United States Army Corps of Engineers. (2021). National Flood Insurance Program (NFIP) Design Standards. Washington, DC: USACE.
- City of Austin. (2025). Climate Action Plan: Water Resources. Austin, TX: City of Austin.
- American Society of Civil Engineers. (2020). Standard Practice for Stormwater Management. Reston, VA: ASCE.
- U.S. Geological Survey. (2024). Hydrologic Modeling Guide. Reston, VA: USGS.
- Texas Department of Transportation. (2022). Stormwater Management for Transportation Projects. Austin, TX: TxDOT.
- National Oceanic and Atmospheric Administration. (2023). Climate Change Impacts on Texas Hydrology. Washington, DC: NOAA.
- World Resources Institute. (2023). Sustainable Urban Drainage Systems (SUDS) Handbook. Washington, DC: WRI.
- Texas Commission on Environmental Quality. (2024). Stormwater Management Program. Austin, TX: TCEQ.
- National Association of City Transportation Officials. (2023). Infrastructure Guide. Washington, DC: NACTO.
- City of Austin. (2026). Sustainable Drainage Systems Implementation Report. Austin, TX: City of Austin.
Appendices
Appendix A provides a concise glossary of technical terms used throughout the manual, ensuring consistent interpretation across all stakeholders. Appendix B contains the full set of hydraulic equations and design curves adopted by the City, including the latest updates to the Manning’s n values for various surface types. Appendix C offers a detailed workflow diagram for the stormwater permitting process, illustrating each approval step and required documentation. Appendix D presents a database of historical rainfall records and runoff coefficients for the Austin metropolitan area, facilitating accurate design input. Appendix E lists all relevant code references and regulatory documents, with hyperlinks to the official sources for quick access. Appendix F supplies a sample forms for site evaluation, permit application, and post‑construction inspection. Appendix G includes a checklist for maintenance crews to verify compliance during routine inspections. Appendix H offers guidance on integrating green infrastructure elements, such as bioswales and permeable pavements, into existing drainage systems. Appendix I provides a case study of a recent high‑profile project that successfully met all criteria, highlighting lessons learned and best practices. Appendix J contains a FAQ section addressing common queries from developers and engineers regarding the manual’s application. All appendices are updated annually to reflect changes in regulations, technology, and best practices, ensuring the manual remains a resource for the City’s water‑management community.
