Trinity Watershed Management


Trinity Watershed Management Department

​​​Flood Plain and Drainage Management​​

Susan Alvarez, P.E., Assistant Director

Program Manager, Steve Parker, P.E., CFM

Oak Cliff Municipal Center (OCMC)
320 East Jefferson, Room 307
Dallas, Texas  75203
(214) 948-4690

The City of Dallas has a comprehensive approach to floodplain and drainage management that dates back to the early 1970s. Through various initiatives, the City has worked with the private, public and non-profit sectors to determine the most feasible approach to managing development in and around floodplains. This approach is outlined in the City of Dallas, Floodplain Regulations(Article V of the Dallas Development Code).

The City of Dallas Flood Warning System and Real Time Gauging Data can be found at City of Dallas Flood Control. Visit the site at any time of day or night.

Residential and commercial development, including earthwork, existing or new structures within the 1% Annual Chance (100-year) floodplain are reviewed and evaluated by the City of Dallas to ensure that the floodplain criteria are met before permitting construction. Property owners may need to obtain fill permits and/or floodplain alteration permits prior to construction activities in a floodplain.

For residential interior improvements, up to 50% of the appraised value of the home structure can be made every 10 years with floodplain management approval. Demolition of a structure (such as a home) within the 100-year floodplain is permitted without a separate floodplain permit but may still require additional building permits. The development and construction of new structures will require a fill permit and final approval by the Dallas City Council. Improvements such as a tennis court, a playground, a swimming pool, a fence, a deck, an erosion control wall, or the installation of significant landscaping can be made through a floodplain alteration permit. To review the requirements of the fill permit application and associated documents, view it here(note that Article V permit fees apply), or please contact Floodplain and Drainage Management at 214-948-4690.

If your property is located in Dallas County, you can estimate if your property is located within the 1% Annual Chance floodplain by searching the Dallas County Central Appraisal District (DCAD) website, by viewing your property in the aerial photo and Flood Plain GIS layer or referring to FEMA’s maps.riskmap6.com website. If your property is not within Dallas County but is within the City of Dallas limits, please call us at 214-948-4690.

If you have questions concerning the floodplain and proposed improvements, you may either contact us or the engineering division of Sustainable Development and Construction in Room 200 of OCMC (214-948-4205).


Download the Floodplain Management Brochure

FLOODPLAIN MANAGEMENT BROCHURE

INTRODUCTION

The City of Dallas is dedicated to minimizing the loss of life and property that is associated with flooding events. Education and prevention are valuable and proven tools that help communities become resistant to these natural disasters.

The City of Dallas recognizes that its entire community is susceptible to flooding, not just those structures located within Special Flood Hazard Areas (SFHA’s). The following information has been provided to help inform property owners located within flood-prone areas and also all property owners with in the City of Dallas.

1. FLOOD HAZARD INFORMATION

The City of Dallas lies in central Dallas County, with outlying areas in Denton, Collin, Kaufman and Rockwall Counties. It has a land area of 386 square miles, and its population is about 1,188,580. Dallas is drained by the Trinity River and its tributaries. Two of the larger tributaries are White Rock Creek, with a drainage area of 139 square miles, and Fivemile Creek, with a drainage area of 55 square miles. The terrain in Dallas is characteristic of the Blackland Prairie. Most of Dallas has developed quite rapidly, but development is picking up in the southern sector.

Most flood-producing storms are experienced in the spring and fall. The typical larger floods result from prolonged or successive storms that produce heavy rainfall, however, severe flooding can occur as a result of intense thunderstorms at any time. Historically, the 1908 flood on the Trinity River was one of the worst, but record floods occurred on White Rock Creek in 1964 and Bachman Creek in 1966. Damaging floods occurred on the Trinity in 1989, 1990, and 1991, and deadly flash flooding occurred in 1995. The most recent widespread flooding was March 19, 2006, predominately in the interior drainage areas behind the levees. Significant flooding also occurred on June 11, 2009.

2. FLOOD SAFETY

1. Do not walk through flowing water.
Drowning is the No. 1 cause of flood related deaths, mostly during times of rapidly rising water. Currents are deceptive; six inches of moving water can sweep you off your feet.
2. Do not drive through a flooded area.
More people drown in their cars than anywhere else. Vehicles also push water into homes and cause additional property damage. Do not drive around road barriers. “Turn around, don’t drown!”
3. Stay away from power lines and electrical wires.
The No. 2 cause of flood deaths after drowning is electrocution. Electrical current can travel through water. Report downed power lines to the power company. Have your electricity turned off by the power company.
4. Evacuate if needed:
If emergency officials tell you to evacuate or leave your home, go immediately to a safe shelter, hotel or relative’s house.
5. Look before you step.
After a flood, the ground and floors are covered with debris including broken bottles and nails. Floors and stairs that have been covered with mud can be quite slippery. Fence planks with nails can wash into your yard, driveway, or city street.

IMPORTANT USEFUL WEBSITES

www.fema.gov
www.usgs.gov
www.nws.noaa. gov
www.floods.org
www.tfma.org
www.weather.gov
www.floodsmart.gov

3. FLOOD INSURANCE

If you do not have flood insurance, talk to your insurance agent. Homeowner’s insurance policies do not cover damage from floods. However, because the City of Dallas participates in the National Flood Insurance Program, you can purchase a separate flood insurance policy and receive a discount. Remember that there is a 30-day waiting period before a policy becomes effective. This insurance is backed by the federal government and is available to everyone, even for properties that have been flooded. Some residents have purchased flood insurance because it is required by their lending institution. Usually these policies only cover the structure and not the contents. In the City of Dallas, there are about 2,400 active flood insurance policies. If you already have coverage, please check to ensure that the coverage is adequate for your property and that the contents are covered as well. Even if you haven’t been flooded in the past, the next flood could be worse. Keep in mind that the policy must be renewed each year.

4. FLOOD WARNING SYSTEM

ALERT is an acronym for Automated Local Evaluation in Real Time, which is a method of using remote sensors in the field to transmit environmental data to a central computer in real time. The National Weather Service developed this standard in the 1970's and it has been used by the National Weather Service, U.S. Geological Survey, Army Corps of Engineers, Bureau of Reclamation, numerous state and local agencies, and international organizations.

The City of Dallas installed 63 ALERT sensor locations and two base station computers in 1990 with the stormwater automation project. Currently the City has 88 sensor locations. We monitor rainfall, stream level, temperature, humidity, wind speed and direction, and lift station status at various locations around the city. The information gathered through this system allows the City of Dallas Office of Emergency Management to plan for and implement emergency evacuations.

5. FLOOD PROTECTION ASSISTANCE

Concerned citizens and the general public can obtain information on flood protection assistance from the City of Dallas Trinity Watershed Management Department Floodplain Management section by calling 214-948-4690. Flood protection assistance provided by the City of Dallas is site-specific flood and flood-related data, data on historical flooding in the neighborhood, and similar information.

Services Provided:

  1. Make site visits to inspect flooding, drainage and erosion problems and provide one-on-one advice to the property owner.
  2. Maintain a database of flood and erosion needs, to be used during bond program development.
  3. Speak to individuals and groups about specific problems and processes, and about maintenance.
  4. Provide a list of engineers with expertise in floodplain and drainage problems and solutions.
  5. Consult with property owners, developers, and engineers about the floodplain permitting process.

6. SUBSTANTIAL IMPROVEMENTS

What is substantial improvement?

The National Flood Insurance Program (NFIP) defines it as any reconstruction, rehabilitation, addition, or other improvement to a structure, the cost of which equals or exceeds 50 percent of the market value of the structure either before the start of construction of improvements or repairs, or if the structure has been damaged and is being repaired, before the damage occurred.

Substantial improvements are not permitted unless the Board of Adjustment grants a special exception based on hardship. Improvements necessary for the sole purpose of complying with federal, state, or local health, sanitary, or building codes, as identified by the local code enforcement official, are not considered substantial improvements. The term also does not include alterations to historical structures.

Floodplain Management staff can provide more information about permitting for improvements of structures within the floodplain. In certain cases, an elevation certificate will be required, in order for us to determine whether the structure is subject to flooding. The property owner is responsible for hiring a surveyor or engineer to prepare the elevation certificate.

7. FLOODPLAIN DEVELOPMENT PERMIT REQUIREMENTS

The Floodplain Regulations, Section 51A-5.100 of Part II of the Dallas Development Code, outline the processes for floodplain alteration and floodplain fill permit requests. A floodplain alteration permit is required for construction of retaining walls, pools, fences, and landscaping that change the topography within the SFHA. A floodplain fill permit is required for the reclamation of floodplain for development. The floodplain regulations may be found at http://www.dallascityhall.com/trinity_watershed/articleV.html

Article V, Floodplain Regulations, outlines the processes and technical requirements for these permits. The criteria in the Floodplain Regulations ensure that projects can be completed with no adverse impact on other properties or on the environment. If you see filling or construction activities without a City Permit, call us at 214-948-4690 or use the city’s 3-1-1 system to alert us.

8. DRAINAGE SYSTEM MAINTENANCE

It is illegal in the City of Dallas to dump any type of debris into creeks or floodplains.

  • Do not dump or throw anything into ditches, storm drains, or streams. Even grass clippings and branches can clog storm water conveyance causing a back-up of water.
  • If your property is next to a ditch or stream, please do your part and keep the banks clear of debris. The city does not maintain creeks that are on private property – it is the owner’s responsibility.
  • If you see dumping or debris in ditches, storm drains, or streams, use the city’s 3-1-1 system to alert us.

If you suspect a storm drainage inlet or culvert is blocked, use the 3-1-1 system to report it, whether or not it is raining. Maintenance of bridges, culverts, and storm drainage systems is more effective if done regularly during dry weather.

9. PROPERTY PROTECTION

You can act now to protect your property from flood damage rather than wait for a flood to occur. Many alternatives are available to help minimize flooding. If the floor level of your property or structure is lower than the Base Flood Elevation (BFE) located on the FEMA Flood Insurance Rate Maps (FIRMs), consider ways to prevent flooding from occurring such as retrofitting your building. “Retrofitting” means altering your building to eliminate or reduce flood damage.

Retrofitting measures include:

  1. Elevating the building so that flood waters do not enter or reach any damageable portion of it.
  2. Flood proofing by sealing the exterior of the structure to prevent water penetration, and elevating outdoor equipment such as HVAC equipment to prevent damage.
  3. Constructing an automatic flood gate or barrier, to protect a low parking garage entrance.

Other useful steps could be:

  1. Moving personal property that would be damaged from the floor to table tops or shelves.
  2. Have plastic sheeting, sandbags, and towels ready so they can be used quickly to reduce seepage through exterior doorways.
  3. FEMA recommends that anyone living behind a levee should have flood insurance. Make sure to carry flood insurance – homeowners’ insurance does not cover losses due to rising water.

10. NATURAL AND BENEFICIAL FUNCTIONS

Floodplains are dry areas that are periodically inundated. Periodic inundation is a natural process resulting from the timing and intensity of rainfall events. Stream channels formed over long periods of time and their size is governed by the more frequent rainfall events, typically those occurring every few months. But a long-term analysis of rainfall events shows that occasionally we can expect to receive much greater rainfall than normal, either in terms of a greater depth of rainfall or a large amount in a very short period of time. Both of these occurrences can and do result in the stream channel being overwhelmed with the result of flooding of normally dry areas nearby.

Dallas uses the 1% annual chance flood (100-year flood) as its design standard, and this is consistent with FEMA criteria. This event has a 1% chance of being equaled or exceeded each year, and is roughly the “worst” flood in a given 100-year period. The 1% annual chance flood will inundate an area consistent with mapping on FIRMs. Looking at the floodplain maps, it can be hard to discern benefits, but let’s look at a few:

  1. The width or spread of floodplain allows utilization of flood storage, or valley storage, and this decreases the flooding that occurs downstream.
  2. In natural floodplains, the area flooded is called a riparian zone, and timely inundation is necessary to support a unique variety of plant and animal life.
  3. As the floodwaters spread out, the speed is reduced so that less erosion occurs. By allowing floodwater to slow down, sediments settle out, thus maintaining water quality.
  4. A natural floodplain left undeveloped provides a greenbelt that adds appeal to nearby developed areas.