ML19329E152

App 2B of AR Nuclear 1 PSAR, Surface Water Hydrology. Includes Revisions 1-18

ML19329E152
Person / Time
Site:	Arkansas Nuclear
Issue date:	11/24/1967
From:	ARKANSAS POWER & LIGHT CO.
To:
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NUDOCS 8005300754
Download: ML19329E152 (7)

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APPENDIX 2-B SURFACE WATER HYDROLOGY 1.0 PURPOSE AND SCOPE In connection with the safety aspects of the proposed nuclear power plant on Dradanelle Reservoir, near Russellville, Arkansas, certain surface water in-vestigations were made. These included the source and dependability of the cooling water supply, location and extent of lakes and reservoirs, the magni-tude of floods, and effect of possible failure of upstream dams.

2.0 WATER SUPPLY The plant site is located on a peninsula on the left bank of Dardanelle Reservoir on the Arkansas River, abcut 7 river-miles upstream frce the dam.

The downstream side of the peninsula is formed by the floeded valley of Illinois Bayou, a left bank tributary to the Arkansas River. The plant will require 1,700 efs for once-through cooling for a one-unit installation or 3,LCO cfs for two units. This water will be taken from the Illinois Eaycu embayment. The 6 discharge will flow into the reservoir south from the plant. (see Figure 2-2 in section 2) Consumptive use will be about 20 efs for the unit.

2.1 OPERATION OF DARDANELLE PESERVOIR Dardanelle Reservoir is part of the Arkansas River navigation project, pre-sently under construction. The project will provide a minimum 9 fsot navigation depth frcm the mouth of the Arkansas River at the Mississippi River to Catoosa, Oklahoma, near Tulsa, on the Verdigris River, a distance of more than 500 miles. There are 17 locks and dams in the system. Thirteen of these are simple locks and dams, providing navigation lifts of 30 feet or less.

Dardanelle, Ozark, Robert S. Kerr, and Webbers Falls Dams (in order from dcwn-stream to upstream) are higher, with lifts up to 5h feet, and include scme storage for hydropower generation.

Upstream from the head of navigation, there are seven large multi-purpose reservoirs. These reservoirs control the flow frcm about lh0,000 square miles of drainag'e area with about 12,000,000 acre-feet of stcrage of which about 6,000,000 acre-feet are reserved for flood control.

Dardanelle Reservoir is 258 miles upstream from the mouth. A navigation lift of 54 feet raises shipping to the top of the power pool at elevation 336 feet.

The minimum navigation pool elevation is 336 feet, providing a normal two feet of storage in the reservoir for power generation Power generation is en the basis of mean daily inflow equaling mean daily outflow, within the 336-338 feet limits.

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jgllh 2-B-1 - '

7-11,68 Supplement No. 6  ;

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2.2 HISTORICAL' RECORDS OF FLOW Daily streamfl'ow records for the period January 1923, to September 1957, col-lected.at the,Dardanelle gaging station just below the dam, have been adjusted by the Corps of Engineers.to reproduce flows as they would have been regulated by the complete' system of dams upstream. The maximum regulated daily discharge during this 35 year period was L80,000 cfs, while the minimum was 400 cfs.

2.3. LOW TLOW It is possible- for the inflow to the reservoir to be zero undervery exceptional circumstances, but these conditions would exist for only a few hours, during which time there would be more.than enough water in storage in the reservoir to supply the comsumptive use of the plant.

3.0 LAKES AND RESERVOIRS IN VICINITY Lakes and reservoirs with a surface area of 100 acres or more within a 50 mile radius of- the site, and det' ails on ownership, location, use, and size of these bodies of ' water are shown in Figure 2-11. No drinking water supplies are taken from the Arkansas River between Dardanelle Reservoir and the mouth at the Mississippi River.

h.0 FLOODS The highest flood experienced at the Dardanelle Dam site occured in 19h3, with a peak flow of 683.000 cfs. Dardanelle Dam is designed to hold a water level no higher than 338 feet to a discharge of about 900,000 cfs. At higher

' discharges, the reservoir level would rise. The levels along the river chan-  !

nel in this area are generally designed for flows of 830,000 cfs.

4.1 b%XIMUM PROEAELE FLOOD The Corps of Engineers has computad the maximum probable flood flow at Dar-danelle Dam as 1,500,000 cfs. At this flow the water level at Dardanelle Dam l

would be 353 feet. The upper end of Dardanelle Reservoir is at Ozark Dam, H about 51 miles upstream. During maximum probable flood conditions, the level of Dardanelle Reservoir at the downstream side of Ozark Dam would be 389.5 feet. No profile for this condition is available, but it is reasonable to assume a straight-line variation. On this basis, the maximum probable flood level-at the plant site is 358 feet.

4.2 FAILURE OF UPSTREAM DAMS The seven storage reservoirs in the headwaters of the Arkansas River are from about 180 to nearly 300 miles upstream from the site. Water from Eufala and Tenkiller Reservoirs must pass through five other impoundments to reach the site; from Keystone and Ft. Gibson, six: from Oolagah and barkham Ferry, seven; and from Fensacola, eight.-In the extremely unlikely event of total failure of one of these dams, the flood wave would be so attenuated by valley and reservoir surcharge storage as to be negligible by the time it reached the plant site.

'It-is considered, therefore, that failure of one of these dams would not con-stitute a hazard to the plant.

()5$Eh b 2-B-2' 2-8-68 Amendment No. 1

The failura of Ozcrk D;m, tha next dam upstream from Dardanelle , presents at maximum power pool level of 372 feet and Dardane gation pool level of 336 feet, there would be a head of 36 feet The following assumptions were made:

1. Ozark Dam fails completely and instantaneously.

2. The flood wave released is 36 feet high.

3. The channel between Ozark Dam and the plant site is of uniform cross-section identical with the section just downstream from the dam .

h. There is no overflow from the channel.

5. No gate changes are made at Dardanelle Dam.

Using these assumptions, the hydrograph of the reservoir level at the site was computed. The maximum rise was about 6.6 feet (reservoir level , 3L2.6 ft) about 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> after the failure of the dam.

All of the assumptions in this analysis are co. servative . Complete and instantaneous dam failures is essentially impossible

. The head above Ozark Dam would be less than 36 feet by the amount of slopee sur- in th face of the 51 miles length of Dardanelle Reservoir

. The cross-section

( than that directly below Ozark. '2here would o er be sufficien open the gates at Dardanelle Dam and lower the reservoir level .

These actual conditions all differ from the assumptions in such a way as to lower the flood level at the site, so that the computed level rep-resents a theoretical maximum value and the true level ably lower.

er- would be c The of standard Ozark Dam wasproject 600,000flood used by the Corps of Engineerse in th design Under these conditions, cfs the and head for Dardanelle Dam it Dam across Ozark was 625 would 000be . cfsonly 5 0 feet.5.0As only feetfailure high, noof Ozark further studyDam at this was made. time would wave release a flood For the maximum probable flood, the head differential at Ozark would be resulting from an Ozark failure tions as for the previous study, except as follows:

was investigated, g

p-using

1. The flood wave released is 11.5 feet high.

2. Locks and Dams 13 and 14 are completely submerged soarge that surch will contribute to the flood. storage upstream to Robert S. Kerr Dam (86.5 0252 M

2-B-3 2-8-68 Amendment No.1 '

This computation indicated a maximum theoretical rise in the water level

at the site of 6.8 feet 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> after the Ozark failure. As in the l

previous case, however, the complete and instantaneous failure of the

! dam is so unlikely as to be practically impossible. All levees would be

overtopped and an additonal estimated 50 square miles would be flooded, providing a great amount of extra valley storage. .It has been estimated l- that the actual rise at the plant site resulting from failure of Ozark Dam would be about 3 feet. Therefore, the failure of Ozark Dam during a maximum probable flood would result in a maximum 361 foot water level.

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02s3 2-B-4 2 4 -68 Amendmai9 TR%.JL