The Cost of Flooding
Major flooding events in 2007 and 2011 caused Mansfield residents and businesses to experience significant flooding from the
Touby Run tributary of the Rocky Fork. These floods caused millions of dollars in personal and business property losses,
as well as disruptions to daily life, lost business revenue, and reduced property values. If we do nothing,
we can only expect continued flooding and loss.
Flooding Solutions and Benefits
The City of Mansfield is proposing to take a major step in reducing much of this flood damage in the future. With the help of experts in flood analysis, the City has developed a plan to reduce the potential for flood damage for the 100-year flood (like the one in 2007), while enhancing future growth and development opportunities, and providing more open space and other community benefits. Through strategically located detention basins, a new earthen dam embankment, and selective bridge improvements, we can greatly reduce the extent of flood damage to residential and business properties. By building the elements of the plan, we will allow for redevelopment and renewed prosperity in a large portion of the downtown area of the City.
Click here for a map showing the existing floodplain and the floodplain after the flood solutions are put in place.
Earthen Dam Embankment
The most immediately recognizable flooding solution will be the earthen dam embankment to be constructed along Touby Run in an area adjacent to North Park. On average the dam will rise 29 feet high above the existing ground and will require approximately 55,000 cubic yards of dirt to build. Under normal conditions, the Touby Run channel will continue to flow through a culvert under the dam embankment. In times of heavy rain, flood waters will become trapped behind the embankment, reducing the flow of water that is carried downstream of the dam. Over time, the flood waters trapped behind the dam will recede and the Touby Run channel will continue to flow through the dam embankment as it does under normal conditions. The dam includes a concrete emergency spillway which would only operate under extreme flood conditions, larger than the August 2007 flood event, to protect the integrity of the dam.
The images below are basic renderings of what the dam may look like.
Click here for a graphic representation of where and how the dam will be constructed.
Expanded North Lake Park Trail
Because of the new earthen dam embankment, a portion of the B&O Trail will need to be relocated. This presents an opportunity to expand the trail and make improvements, including a scenic pedestrian bridge, an additional primitive trail meandering through the wooded area, and other park amenities.
Click here for a site plan of the North Lake Park Trail improvements.
Project Funding: A Fair Approach
The estimated cost for building and maintaining the flood control solutions along Touby Run is approximately $14.5 million. Paying for the construction and ongoing maintenance of the flooding solution will come from a combination of sources. Grants from state and federal sources may be obtained, but can only cover a part of the cost. Most of the project funding must be local, which means a charge to all property owners within the City. The amount charged to each property owner is based on where the property is located and the amount of impervious area (hard surface) on the property.
Draining to the system:
The amount collected from each property owner is based on how much that property contributes runoff to the stormwater system. The stormwater system collects the rainwater that runs off of hard surfaces such as roofs, driveways, parking lots and sidewalks. Flooding happens when there is more runoff than the system can handle. So, the more hard surface a property has, the more it contributes to water in the stormwater system. The measurement of how much a single-family property contributes to the system is called an Equivalent Residential Unit, or an ERU.
All single-family home property owners in the City will pay for one Equivalent Residential Unit, or an ERU. A typical ERU represents approximately 2,800 square feet of hard surface.
Commercial property owners will be responsible for more than one ERU, due to larger roof area, parking lots, and walkways, all adding up to more hard surface area and more stormwater runoff. Each commercial property will be evaluated independently to determine their number of ERUs. For example, if the total amount of hard surface for the property is 16,000 square feet, then the total number of ERUs is 5.71 (16,000 divided by 2,800).
Location of the property:
The effects of the flooding, and the benefits provided by fixing it, are also directly impacted by a property’s location within the City. Improving the economic prosperity of the City of Mansfield benefits all residents and business owners. However, the benefit varies based on proximity to the Touby Run watershed and floodplain. Our initial investigation of rates charged to individual property owners has established these three zones:
Less than $1 per month
Improving the economic prosperity of the City through reduced flood damages benefits all residents and business owners. All property within the City will be assessed the minimum fee to fund the flood hazard mitigation project. For single-family home owners, that is estimated to be less than $1 per month.
Click here for a map view.
Between $2 and $3 per month
All property within the Touby Run watershed is contributing stormwater runoff which will be controlled by the proposed flood hazard mitigation project. For this reason, all property within this zone will be assessed an additional fee to the minimal fee described above. For single-family home owners, the total fee is estimated to be between $2 and $3 per month.
Click here for a map view.
Between $7 and $8 per month
All property within the existing 100-year floodplain of Touby Run is receiving the largest and most direct benefit of the flood hazard mitigation project. For this reason, all property currently within the floodplain will be assessed an additional fee to those in the Touby Run watershed. For single family home owners, the total fee is estimated to be between $7 and $8 per month.
NOTE: As noted previously, commercial property owners will pay a multiple of the single-family rate based on the measured amount of impervious surface (hard surface).
Click here for a map view.
The benefits of reducing future flood damages include increased property value, lower flood insurance costs, economic revitalization, and improved safety, health and welfare for residents and business owners. All of Mansfield benefits when our property and businesses are safe from flood damage.
Send comments on the Touby Run Flood Damage Reduction Program to firstname.lastname@example.org.