MUNCIE, Ind. – The Federal Emergency Management Agency (F.E.M.A.) has a number of conditions that must be satisfied for a section of a Levee (a “Reach”) to regain certification. One of these conditions is that the Muncie Sanitary District (MSD) must show the protected area behind the levee reach must be able to effectively deal with at least a 10-year (which means there is a 10% chance that a storm this large will hit that area every year) rainfall event when the river is at flood stage (and no stormwater behind the levee can escape via a gravity sewer outfall because the flap gates are closed by the river water pressure). The only way stormwater trapped behind the levee can be sent to the river is by pumping, and basically forcing, it into the water.
In the case of the Walnut St./Columbus Ave. area (shown on the photo below), the Army Corp did attempt to address this in the late 1940’s by constructing a storm sewer along Columbus Ave. from Madison to the alley between Walnut and Mulberry Streets, then running that storm sewer south and west to the Flood Pumping Station near the MSD building along the river (the “High St. PS Outlet” shown on the photo below).
Unfortunately, this older flood prevention system in this area is undersized when new FEMA mandated flooding models and design storms are taken into account. The MSD had this area remodeled under the present FEMA/Army Corp design event criteria and the dark blue shaded area on the graphic indicates the area that would be flooded during a 10-year storm. Note that a far greater area than what is shown in dark blue would be flooded with a greater storm event – and at least 4 storm events larger than a 10-year storm have hit the Muncie area in the last 20 months (although the river has not been at flood stage during those recent isolated rainfall events).
There are three options as to how to address the predicted condition with FEMA.
The first is to remove the older storm sewer pipe in this area and replace it with much larger pipe, as well as increasing the size of the pumping station (MSD currently has 3 pumps with a combined pumping capacity of 14 MGD). This would be expensive and disruptive to the area during construction.
The second is to retain and hold back the excess stormwater and bleed it into the undersized flood control system at a rate it could handle.
The third is to take no action and begin having the homes and businesses (including Muncie Central) pay FEMA flood insurance.
The MSD has elected to proceed with the second option – but will utilize green infrastructure practices on parcels of property that it would acquire over time in order to capture, hold, and then release the stormwater at a rate where the existing facilities could handle it.
This can be done by purchasing clusters of homes in these areas and installing pre-engineered underground stormwater storage vaults on those lots. The curb inlets on the streets would direct the first flush of stormwater to the existing storm sewer system and would then direct the excess flow to the underground storage vaults on the acquired parcels. The system would be designed to function during the larger rain events in the future.
MSD decided to acquire property in this area when there were willing sellers and made it a priority to buy the houses in clusters and, ideally, in low spots in this area where the stormwater would naturally collect. MSD’s schedule is to acquire property in this area until mid-2018, then hire an engineer & landscape architect to design this area based on the property parcels MSD has purchased by that time. The actual stormwater project would be constructed along with the next round of Combined Sewer Overflow Long Term Control Plan (CSOLTCP) projects, due to start implementation in 2020.
This urban green infrastructure concept is being done in Indianapolis, Columbus, Cincinnati, Louisville, and many more communities as part of CSOLTCP and FEMA compliance.
About Muncie Sanitary District
The Muncie Sanitary District (MSD), created under Indiana State law in 1968 by the action of an Ordinance of the City of Muncie, Ind., provides services to the public in the areas of code enforcement, engineering, sanitation, sewer maintenance, storm water management, water pollution control and recycling. In addition to these services, the MSD maintains a statewide position of leadership in green infrastructure through its commitment to programs and initiatives that make the Muncie community a better place to live.
Muncie Sanitary District
300 N High St., Muncie, IN 47305