Questions and Answers

Listed below are answers to some questions we have been asked about this flood control plan

1. Is regulation of the reservoir necessary in order to protect homes and businesses north of downtown Jackson?

No. The flood control lake will do this alone. Without any improved reservoir discharge regulation the 1979 flood levels would be lowered over nine feet.

2. What makes the flood control lake so effective?

The flood control lake corrects for a very large blockage to flow created when bridges and levees were added to the flood plain in downtown Jackson. About five feet of the flooding north of downtown Jackson is due to the back up of water against these structures. This additional five feet of man made flooding gives the flood control lake a lot to work with.

3. Why is the flood control lake so much more effective in providing protection to north Jackson homes and businesses than businesses in downtown Jackson?

This is because the homes and businesses north of downtown Jackson were built at the base of the hills in areas that were above the valid 100 year flood level originally. Many structures along Town Creek were built in flood prone areas that historically flooded.

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4. What effect did the reservoir have on flooding during the 1979 flood?

Loss of flood plain capacity (about 10 billion cubic feet) was offset by holding five billion cubic feet in the reservoir during the period when greatest flow occurred.

5. Can the reservoir do more to prevent flooding downstream?

Yes. By lowering its level to 292 feet during the early stages of major flood events.

6. Why is the reservoir not doing this at this time?

The lower lake must be built first. The lower lake enables the reservoir to discharge at high rates without backing water up into northeast Jackson homes.

7. Would this lowering be done on a frequent basis?

No. Lowering to this level would not occur more than once every 25 years.

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8. What would happen in the other 24 years?

The reservoir would be kept at 296 feet even in flood prone months. Two or three times each year its level will drop to 295 feet and rise to 296 over a period of two days. It will not deviate from this procedure unless a 25 year flood rain is on the ground.

9. Would it be difficult to know when to lower the reservoir to this level?

No. A river the size of the Pearl requires over a day for the rain event to occur and several days for the flood to develop. Modern monitoring systems would transmit rainfall data in time to make accurate judgments about the size of a given flood. The size of a given flood is not critical, just that it be over a 25 year rainfall measured on the ground.

10. Is it critical that the rain measurements and reservoir inflow predictions be accurately measured?

No. Taking the reservoir down to 292 feet once every 25 years will take 1-1/2 feet off of any flood event whether it be a 25 year flood or a 200 year flood.

11. Is it critical to accurately fill the reservoir during a major flood so that it becomes full concurrent with the crest of the flood.

No. Relatively large changes in discharge rates made in order to adjust to inflow will have relatively little effect on a downstream flood plain that is full of water. The crest of the flood would be the product of the long term average discharge. The long term average discharge is the product of how low the reservoir is taken down to and how high it is filled up.

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12. Does using the reservoir to take one foot off of major flood qualify it as a flood control lake?

Yes. Its possible to use the reservoir holding capacity (8 billion cubic feet) to more than offset the loss of holding capacity in the original flood plain (10 billion cubic feet) by coordinating the time that the capacity is used to the period when the flood rates are greatest.

13a. What effect will the comprehensive plan have on flooding in Byram?

1979 flood levels would be lowered about 10 inches.

13b.  What effect will the comprehensive plan have on flooding in Richland?

1979 flood levels would be lowered about 11 inches

13c.  What effect will the comprehensive plan have on flooding in the Lynch creek area?

1979 flood levels would be lowered about four feet

13d.  What effect will the comprehensive plan have on flooding in the Town Creek Area?

The 1979 flood levels would be lowered about five feet

13e.  What effect will the comprehensive plan have on flooding in the Lakeland area?

The 1979 flood levels would be lowered about 10 feet.

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14. How will we know what structures in these areas would not be protected from a 200 year probability such as the 1979 flood?

By surveying and documentation

15. What will be done about these structures not protected from a 200 year flood?

Additional protection will be provided when warranted.

16. Can the lake plan be made to give 200 year protection to 100 percent of the structures in the Jackson downtown area and in the Richland area?

Yes, by extending the flood control lake south to just above Byram, eight feet less flooding would occur during a 200 year flood such as the 1979 flood in downtown Jackson and three and one-half feet less flooding would occur in Richland. This would eliminate all flooding in the metropolitan area in another 1970 flood.

17. Would Richland be expected to pay for part of this flood control plan?

We shouldn’t think so. The benefit to Richland in this plan is less than one foot with the smaller lake plan . If the lake were extended south of Richland or if levees are added to the plan in order to increase the protection in Richland from a 100 year flood to a 200 year flood, we should think that Richland would be expected to pay a part of that.

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18. What level of protection will the present comprehensive plan provide to 100% of the structures from Byram to the reservoir?

The plan will provide protection from a 100 year flood.

19. How do the costs of the flood control lake plan compare to the Shoccoe dam plan?

The 1984 cost for Shoccoe was estimated to be 85 million dollars. The 1997 cost for the flood control lake is 80 million.

20. How do the flood control benefits compare?

Both plans provide benefits by reducing flood levels as follows:

21. Does the Shoccoe dam create any growth potential to offset its cost?

No, it causes additional flooding on 50,000 acres north of the reservoir.

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22. Does the flood control lake require the relocation of many homes and businesses?

No. The lake will effect practically none because it only occupies the river bottomland and lowers flood levels everywhere. For example, where the levee plan would increase flood levels at Lakeland and provides for the total acquisition of some 30 commercial buildings in this area, the flood lake would lower 1979 flood levels 11 feet. This would completely eliminate flooding in this area.

23. Does the proposed levee project create growth potential in lands protected by the levees.

No. The undeveloped land protected by the levees would be needed for ponding reserves. Restrictions would be placed on any growth in these areas. The land between the levees would be unusable for almost any purpose (see land above and below Hwy 80 and I-55 bridges) and all land above the new levee system would be condemned for the reason that extra flooding would occur there after the new levees are constructed.

24. What growth potential would result from construction of the flood control lake?

All of the flatwood portion in the metropolitan area of the flood plain (10,000 acres) would become developable land. The 600-acre island would create a new waterfront addition to downtown.

25. Will the cost of the project result in additional taxes?

No. This project will replace current plans for flood control and traffic improvements, which add, up to more tax burden and do not solve the whole problem.

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