There are four major drainageways across the city, not including the Elm Fork of the Trinity on the western boundary of Carrollton. The Elm Fork is managed primarily by the City of Dallas and the City drainageways are managed by the City of Carrollton.

Overall, flooding in Carrollton is buffered by Lake Lewisville and Lake Ray Roberts and, to a lesser degree, Lake Grapevine.

• These reservoirs are controlled by the Army Corps of Engineers to reduce the peak flows into the Elm Fork of the Trinity, allowing city drainage to flow more freely.
  
  
• Even with the emergency releases from Lake Lewisville in 2015, the City had minimal flooding outside of known flood prone areas.  

What is floodplain management?

Strategies and actions that aim to reduce the damage caused by floods, protect the natural function of floodplains, and use flood risk information to inform planning decisions. 

Components of Floodplain Management

• Flood Hazard Identification and Mapping
  
  
• Regulatory Measures
  
  
• Structural Measures
  
  
• Non-Structural Measures
  
  
• Natural and Beneficial Functions

• Protect life and property
  
  
• Ensure public safety
  
  
• Minimize economic losses
  
  
• Preserve the natural environment

Channel Improvements 

• Most of the channels in Carrollton have been improved using stone, concrete blocks, and concrete.
  
  
• These improvements in the last several years have been permitted through the US Army Corps of Engineers as part of Section 404 of the Clean Water Act.  
  
  
• In short, the 404 Permit puts extensive restrictions on any modifications to the channels along with requirements for vegetation and ultimate stabilization.

The channels throughout the City are analyzed on a routine basis. This analysis considers several factors, including the vegetation along the channel slopes to determine a flood elevation for a particular design flood.

• Vegetation for the channels must be of certain types that are considered native to the area. This vegetation must be allowed to grow and spread throughout the channel area.
  
  
• This provides protection of the typically highly erosive banks along the creek as well as wildlife habitat areas. It is also a condition of the Section 404 Permit. 
  
  
• There is no provision for cutting this vegetation as part of the permit. We do cut it back when it becomes detrimental to the flow in the channel.

• The City implements the concept of ‘higher standards’ in the flood criteria for new developments. This includes requiring finished floors to be 2 feet above the 100-year flood plain (the National Flood Insurance Program (NFIP) requires 0.0 feet) and requiring that any floodplain reclamation has no offsite increase in flood elevations (NFIP is up to 1 foot increase).  
  
  
• We continue to aggressively manage drainage. We are looking at a full, city wide channel modeling update and master plan in the next year or two. We are also looking at developing a rain gauge / river gauge system to assist in Emergency Management operations.
  
  
• We typically have a channel improvement project under construction each year to reduce erosion and improve flows.
  
  
• We participate in the North Central Texas Council of Governments (NCTCOG) Corridor Development Certificate program, which limits development in the Trinity River basin (including Elm Fork) to maintain manageable peak drainage flows.  

Feel free to contact the City’s Floodplain Administrator, Matthew Brennan, P.E. at 972-466-3183 if you would like further information.

• The City participates in the NFIP (National Flood Insurance Program), a federal program that establishes design criteria for flooding (1% chance or 100-year rainfall intensity) to determine flood elevations and floodplain / floodway limits.
  
  
• The City also participates in the Community Rating System, a voluntary program where insurance credits for homeowners are earned through activities the City implements to reduce flooding possibility – these include design parameters for buildings as well as maintenance of channels.
  
  
  • Local community ratings are based on 18 activities, organized under four categories:
    • Public Information
    • Mapping and Regulations
    • Flood Damage Reduction
    • Flood Preparedness
      
      
  • The City has a rating of 6 on a scale of 1 (excellent) to 10 (no activity). This is one of the better ratings in the Metroplex.