ANSWER TO U.S. CORPS OF ENGINEERS
CONCERN NUMBER 8

Extensive development of the flood plain could conflict with Executive Order 11988. Corps policy emphasizes formulation of projects which reduce flood damages to existing development and do not promote development of flood plains and natural areas.

 

    The flood control lake will occupy only river bottomland. Under the existing levee plan, trees will be eliminated between the levees. As seen from the I-20 bridge all vegetation between the levees south of the cutoff channel have been deadened with herbicides. This has created an unattractive and unhealthy situation in a densely populated metropolitan area. Replacing this with a lake should be more environmentally friendly.

     The land outside the new levees would eventually be developed just as it has been developed outside the present levees at Flowood and the fairgrounds. Pressure to develop these areas had been so intense that riverbottom land outside the levees that had been originally dedicated for ponding reserve has since been developed. The YMCA and Residence Inn are built in this original reserve. These structures are almost 10 feet lower than the fairgrounds land creating a need for pumping that would not have been necessary under the original corps plans. This type activity (as in Issaquena County on the Mississippi Levee System) is a continuing problem with all levee systems.

     This project would create about 9,000 acres of developable land out of the flatwood portion of the floodplain north of Jackson. 7,500 acres of this newly developable land is not a natural area. This land on the east side of the Pearl is presently used as a clear cut pine timber plantation. The 1,500 acres on the west side of the Pearl River is adjacent to the northeast Jackson neighborhoods that flooded in 1979 and 1983. This land has blocked drainage caused by sewer mains, sewer lagoons, electric transmission lines, and riversand deposits, there has always been a mosquito and drainage problem in these areas.

     Any true loss of natural area could be mitigated with the creation of better natural resources on land in more suitable areas.

RETENTION VS. CONVEYANCE

     There has evolved, in recent times, a strong school of thought which teaches that flooding can be controlled by the retention of water in green areas and wetlands within floodplains. Believe in this concept has lead to harsh restrictions by government upon how citizens may use property. However, to our knowledge, no attempt has been made to define, through formulation, the exact quantitative amount of benefit that wetlands and green areas provide. If proof of benefits had been required, this is what would have been discovered:

     Wetland and green areas which are situated in vast, flat deltas reduce the level of flooding in bayous and rivers that extend below them by retaining water. When situated in the fast flowing upland river floodplains such as the Pearl in Jackson, wetland and green areas do not flooding in the same manner.

     Water retained within these floodplains, at ground levels, actually has no effect upon the high magnitude floods which cause harm to people. This is because the reaction that results from water's retention or detention in these floodplain green areas cannot be timed to coincide with the higher magnitude floods, which occurs later. The reaction happens too early and seperates itself from the flood that follows by moving away downstream. For this reason, the reaction to ground wetlands and green areas in Jackson's floodplain, does not accumulate to any later benefit. Water retained in the initial stage of runoff does not lower the higher stage, damaging floods, that occur at a later time. Only water retained at higher stages affects the magnitude of a damaging flood. For this reason, on the Pearl, only structures that elevate water to and above the maximum flood heights (such as the Ross Barnett Reservoir) can affect the ultimate level of such floods.

     However, water retention can be used to reduce high magnitude flood levels when the retained water is situated to have its effect concurrent with the high stage. But the actual, formulated benefit that water retention provides is disproportionately small when compared to its cost in labor and resouces. For this reason, retention methods can rarely be justified. On the other hand, when conveyance is improved by construction of ditches and canals, benefit is disproportionately large when compared to cost.

     For example: The U.S. Army Corps of Engineers had proposed building a dam above the Barnett Reservoir at Shoccoe. This retention project would cause 51,000 acres of rural land to be inundated with water during flood events. The project would also utilize the ability of the reservoir to retain water by filling it to its maximum safe level. This would add 38,000 acres. Yet the loss of this 89,000 acres of rural resource to flood control by retention would only provide Jackson with a benefit of reduced flooding amounting to 2000 acres in another 1979 flood event. Flood levels would be reduced 6.6 feet at Lakeland, leaving numerous homes and businesses in North Jackson still flooded.

     By comparison, for less expense, the conveyance of water through the Jackson Metropolitan area could be improved by dredging a canal and, in order to prevent regrowth of trees, making the canal into a lake. This would remove 11 feet of flooding from Northeast Jackson and 4 feet from the Town Creek area. This would end 98% of all flooding in another 1979 flood. In addition, 10,000 acres of land, which previously flooded, would become available for development and, through industrious use of the dredging material, a valuable island would be created.

     The use of retention to control floodin by preserving green areas and wetlands has become very popular and coincides with contemporary society's appreciation for the natural environment. The use of retention, however, if formulated, seldom has any effect on damage causing floods, and retention projects that do have any effect, most often, extract a net loss from the total hunam resource. For this reason, flooding has been, and always will be, primarily controlled by improving the land's ability to convey water by the construction and maintenance of canals and ditches.

The picture below was taken from the I-20 bridge looking northward toward the Highway 80 bridge. The upper right corner of the picture shows the river channel flowing under the Highway 80 bridge. Notice the downtown skyscrapers in the upper left portion of the picture. Natural sand levees formed adjacent to the river channel prevent the flow of water back into the river. This creates the pockets of stagnant water seen in the central portion of the photograph. Mosquitoes breeding in these stagnant pools of water, which extended throughout the entire populated metropolitan area, have contributed to the city’s health problems including several outbreaks of encephalitis over the past decades. It is very difficult to drain these wet pockets because, during flood, the redistribution of sand blocks the drainage again.

The levee plan called for spending an additional 9.8 million dollars to make a recreation area out of this type land with facilities such as inline skating trails. The reader can see how difficult it would be to maintain facilities such as these on land such as this between the proposed new levees.

The photograph below was taken from the Highway 80 bridge looking north toward the downtown skyline. The river channel flows thru the central portion of the picture. Just to the right of the river channel the reader can see a high natural sand levee that follows the edge of the river channel. Just to the right of the natural sand levee, the reader can see the trapped stagnant water on the Rankin County side of the river. The flood control plan would replace this area with a lake almost one-half mile wide.