U. S. ARMY CORPS OF ENGINEERS

1997 ROSS BARNETT RESERVOIR OPERATIONAL ANALYSIS

The Corps’ analysis defines operating parameters for the reservoir and concludes with the following statement:

"The construction of the proposed Jackson Metro Area levees would allow significant improvement (by the reservoir) to both the current bank caving operation results and the optimized results. By allowing a higher pool level to be held year round, significant improvement would be gained, especially in the critical bank caving months of April and May. Model results show that this alternative in conjunction with the above improvements to reservoir operation would result in higher wintertime reservoir pool levels, flood protection for the City of Jackson, decreased river stages downstream of Jackson, and significant improvements to rates of fall at the Jackson gauge."

Our study does not arrive at the same conclusions; we believe that:

1. Levees across Jackson’s major creeks will not provide flood protection to lowest lying structures and streets in downtown Jackson (page 59 – 66).
2. Conditions, created by the new downstream levees, will require that wintertime pool levels be lowered in the reservoir (pages 59 - 66).
3. Reservoir operation in conjunction with the proposed new levees will not lower river stages downstream of Jackson (pages 59 and 60).
4. A high reservoir pool does not improve bank caving procedures. A low pool does (page 90 - 94).

We also believe that progress toward finding the best solution to Jackson’s flooding problems can only be made when contradictions, such as the above, are resolved. We have sent this analysis to the U. S. Army Corps of Engineers for their consideration.

LEVEES EFFECT ON RESERVOIR PRERELEASE

It is obvious, from reservoir spillway operating logs of the 1983 and 1979 floods, that, should levees be constructed across Jackson’s major creeks, effective prerelease of the reservoir would not be possible. Actually, re-enactment of the 1983 flood, reveals that (with levees opposite Lynch and Town Creek) flooding of streets, homes and businesses would have occurred anyway (see pages 59 - 66).

This happens because discharge from the reservoir elevates water levels between the levees. The tributaries flowing into the Pearl, such as those in downtown Jackson, must rise to river levels in order to flow through the levees. Water flowing in Town Creek, which has insignificant ponding reserve, must rise to whatever level exists between the levees at any given time in order to flow out. This means that, when levels within the levees are higher than structures along Town Creek (and when flow remains in the creek and watershed) these structures will flood.

By way of example we modeled the 1983 and 1979 flood assuming that the proposed levees had been built. This modeling revealed that river elevations must be kept low during the period when rain is falling and creeks are running out. Experience with both the 1983 and 1979 floods shows that, during this critical period, release from the reservoir will need to be constrained in order to lower levels between the levees. This will require filling not lowering the reservoir.

You cannot prerelease the reservoir while there is an ongoing rain event in Jackson. In addition, flood history confirms that (at such time as the creeks have run out) reservoir inflow will be to great to allow effective prerelease (such as happened in 1979). Therefore, when the flood crest enters the reservoir (two to three days later) higher-than-ever discharge rates will be required to prevent over filling of the reservoir. This will increase downstream flood levels.

During the period after water has run out of Jackson’s major creeks (six to eight hours after rain ends) levees may protect Jackson. This is providing that no subsequent rain occurs (as did not in 1979) or, flooding may occur anyway (from subsequent rain as happened in 1983).

With levees opposite Jackson’s creeks, higher flood levels will occur downstream of Jackson due to two sources: increased discharge rate due to depleted capacity in the reservoir and increased flow rate resulting from loss of capacity in the north Jackson floodplain. Extension of levees north and south of Jackson will exacerbate this problem.

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RE-ENACTMENT 1983 FLOOD WITH LEVEES AT

LYNCH AND TOWN CREEKS

Rainfall is based upon the average of rain measured in Jackson and at the reservoir. Outside levee ponding (37.35 gauge) 271.05 feet (see next two pages) is estimated in downtown Jackson. Damage levels in the downtown Jackson area estimated as follows:

EFFECT OF LEVEES ON TOWN AND LYNCH CREEKS

1983 FLOOD

Rainfall calculated as the average of measurements at Jackson and at the Reservoir. Watershed (the total of both creeks, 24 square miles (660 million square feet) ponding area at 260.0’: 48 acres; ponding area at 270’: 262 acres: Watershed runoff 75% in 6 hours, 100% in 12 hours

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PREVENTING FLOODING IN LYNCH AND TOWN CREEKS

About 40 commercial buildings, such as workshops and warehouses on South President and mechanic shops on Rankin Street, have been constructed at such low elevations that they have historically flooded every ten years. For many it was a business choice to build these structures so low. (A mechanic may prefer to place his tools up and hose down his shop rather than have his customers negotiate a drive ramp.) Many people do not build commercial buildings above the 100 year flood level. For Example: Lakeland Drive was topped by the 1979 flood, yet since this flood occurred, Schlotzky’s Deli and adjoining strip malls have been built, at levels 3 feet low to this highway. This was done by choice; these business owners did not want their customers climbing eight sets of stairs for 15 generations in order to prevent one occurrence of flood damage, which could be repaired with soap, water and a new coat of paint.

The flood control lakes, by themselves, will remove 3-1/2 feet of flooding in another 1979 flood. Reservoir inflow projections (that we plan to use for better regulation of the reservoir) have been perfected to the point that extra benefit can be considered a given. The reservoir will provide an extra 1-1/4 feet of flood benefit. The combined benefits of the plan will take 4-3/4 feet of flooding out of Town Creek area in another 1979 flood with the lakes in place, (Town Creek’s lowest most structures will have one foot more protection than business owners are willing to provide for themselves when they build today on Lakeland Drive).

This plan will protect all of these lower-most structures from a 60 year flood such as occurred in 1983 (a six fold improvement). Less than ten structures will flood in a 100 year event (see map at back of folder). In another Easter flood (a 350 year event), these extremely low structures will receive about two feet of water (instead of the nearly eight feet that they received in 1979). This amounts to approximately 85 very low structures shown on the 1979 (350 year) map in the back folder of this report. Out of approximately 2000 structures that received water during the 1979 flood, these 80 structures represent most of the structures in the entire metropolitan area that would flood in another 350 year event with the two-lake plan in place.

The fact that the plan does not protect 100% of the downtown structures from a 350 year flood provides the U. S. Army Corps of Engineers with its primary criticism of the lake plan’s technical features. The Corps believes that levees will protect 100% of downtown Jackson, but this is not so. Flooding would have occurred, even with levees in place, in 1983 (see page 17).

We will present this plan to business owners on Lynch and Town Creek to determine their opinion as to the adequacy of the flood reduction provided by the flood control lake plan.

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PREVENTING FLOODING DOWNSTREAM OF JACKSON

Homes and businesses in both north Jackson and Richland were built above the 100 year flood. Yet, in 1979, a 350 year flood placed two feet of water in Richland yards and eight feet in north Jackson yards. The extra six feet of flooding in north Jackson resulted from backup of water caused by levees and also by tree growth between the levees. To a lessor extent, increased flooding was caused by bridges, railroads, sewer lagoons and sanitary landfills that had been placed in the floodplain after homes had been built.

The 200 homes that flooded in Richland received a foot or less water in a flood that will occur once every 15 generations. Most of these homes, which will not last 350 years, are safe from 100 year floods. As north Jackson citizens, who have also suffered flood losses, we know better than to minimize the losses suffered by other people and would never force our opinions upon them. But we believe we can help.

Our plan - lakes through Jackson - will create an ability for the reservoir to prerelease five billion cubic feet of water in advance of major flooding without flooding anything. This will have the effect of lowering flood levels in a similar 1979 flood by up to 0.9 feet in Richland and in communities farther downstream. This would leave very few homes exposed to flooding. If Richland would prefer to spend the 9 million allocated by the Corps for levees, we believe that north Jackson should support them. However, it may be that, with the improved reservoir regulation, only 60 homes would flood. This would work out to be 150,000 dollars per home to prevent flooding once every 350 years.

This plan is not intended to replace or interfere with any plans which downstream communities may have at this time or in the future to advance their own plans for flood control. We will ask members of the downstream communities to give us their support for this plan based upon its intended purpose to reduce flooding in their communities.

TREE CLEARING WITHIN THE LEVEES

The current levees system is not supposed to work with trees. FEMA maps calculate flow between our present levees using short brush friction factors. The levee board attempted to remove some of the trees and was shut down by the U. S. Army Corps of Engineers for disturbing wetlands. New levees, proposed by the U. S. Army Corps of Engineers call for extensive clearing of trees. Experience has proven that these areas grown back in even tighter, more flow restrictive form. The Levee Board, which has had 30 years experience with these problems has recommended consideration of the lake plan to the U. S. Army Corps of Engineers. (See letter enclosed).

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WETLANDS – HARDWOODS
LEVEES

LAKES (4500 ACRES)

INCREASE FLOODING IN OTHER AREAS

Levees

NOTE: Does not include acreage required for ponding, retention outside levee

Lakes

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