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Garrison. It was also important to the economics of the project, the entire Missouri River plan, and the region that maximum power head be provided at Garrison.
On the other hand, it was also essential that the Garrison pool not be so high as to adversely affect the city of Williston and the railroad, or the irrigation districts if local interests desire that they be saved.
The final height of Garrison Reservoir, with the elevation 1,850 maximum normal operating pool (which was recommended in, and authorized on the basis of, House Document 475 and Senate Document 247, 78th Congress) was selected on the basis :
(1) That the 1,850 pool would provide adequate control of the flow and sediment from the Yellowstone River, would provide reasonably for the Diversion from the Missouri River, and would provide the maximum practical power head at Garrison.
(2) That with this height of pool there was no question but that adequate protection could be provided for the city of Williston, the railroad, and other improvements in the area including the irrigation districts units.
(3) That the cost of providing the protection would be amply justified by the additional benefits of having the reservoir at the 1,850 level rather than at the lower level (about elevation 1,830) at which protection works would not be required in this area.
With respect to the third point above, I wish to emphasize that although it might be substantially less expensive to negotiate a settlement for inundation of the irrigation districts' lands, there has never been any question about the fact that the additional benefits of the higher reservoir are more than ample to justify the additional project costs required to pay for protection of these irrigated lands.
I know there has been quite a bit of discussion in past year about authorization of the 1,850 pool, and also its economic justification. I will refer you to the following testimony in previous years hearings which specifically establishes the authority for the 1,850 pool and the overall justification of the authorized level:
Senate subcommittee hearings, civil functions appropriation bill, 1950 (H. R. 3734) pages $55 and 1679–1684.
Senate subcommittee hearings, civil functions appropriation bill, 1954 (H. R. 5376 pages 307–309.
The Department of Interior, by letter dated June 1, 1953 has advised that the Bureau of Reclamation feels Garrison Reservoir should be operated at a maximum normal operating pool elevation of 1,850; and that this will be most advantageous to accommodate the Diversion into North Dakota.
HEIGHT OF PROTECTION REQUIRED The fact that Garrison Reservoir is being built for maximum normal operating pool at elevation 1.8.50 does not mean that water always will be at that level. The reservoir level will rise and fall continually, to fulfill the rather complex detail operating requirements of the entire main stem system. The integrated operation of all the Missouri River main stem reservoirs has been carefully worked out by our own expert hydraulic engineers in the Corps, with the collaboration and advice of engineers of the Bureau of Reclamation, Federal Power Commission, United States Public Health Service and other interested Federal agencies, and in consultation with representatives of the interested States. I have here a chart (attached) to illustrate the initial filling of the Garrison Reservoir as taken from the detailed studies, assuming years of about average river flow from 1954 through 1990. Water levels shown are at the dam. With subnormal flow, of course, the filling rate would be slower. High flow or major flood years simiwhich shows the way reservoir levels would fluctuate by 1970 for all the difwill note that for most of the years the level at the dam varies between elevations 1,838 and 1,845, with a rise to about elevation 1,850 every 5 to 10 years, on
Now, water levels at the head of the pool may be a few feet higher than at the dam when there are high river inflows, because of so-called backwater effects. Backwater pileup above flat-reservoir pool level occurs in the headwater reach of any reservoir as the river slope flattens and the velocity of flow decelerates. The first step in selecting protective grades in the Williston reach of the reservoir, therefore, has involved a hydraulic determination of the maximum levels
to which water might rise at various points along the river for the various combination of pool level and river inflow which might reasonably be expected. This step our hydraulic engineers have accomplished with precision.
In addition to a slight rise in water level along the headwater reach of Garrison Reservoir which may be caused by backwater effects, it appears that some of the sediment carried into the backwater area by the river may settle out in the river channel, and cause some additional slight rise in water levels. This process is called “aggradation.” Aggradation can happen under any conditions which cause lessening of the sediment-carrying capacity of a silt-laden river. It can happen below a dam, above a reservoir, or in a river reach which becomes overgrown densely with trees and brush. We have carefully reviewed experiences on other rivers, but can find no instance of troublesome aggradation for conditions similar to those at the head of Garrison Reservior. However, our analyses indicate that there may be an additional rise, above ordinary backwater, of a few feet in the first few decades of project operation. To insure the adequacy of the protection works proposed, we have added an allowance of 5 feet for additional rise in water level which might result from aggradation.
To obtain the greatest assurance that the Williston problem is correctly solved, we have employed the world's outstanding experts in this field. The allowances provided for aggradation, in the design of the proposed protection works, have their indorsement.
To sum up, the height of protection works proposed is based on the levels to which water would rise under the backwater conditions which would result from the most severe reservoir levels and river intlows reasonably expected. To these levels a 5-foot allowance for possible aggradation and the normal structural freeboard of 3 feet for the Williston levees, and 2 feet for the irrigation unit levees (in accordance with normal Corps practice for urban and agricultural levee systems), have been added to obtain the top of levee grades. Levees built to these grades will provide very adequate protection from any adrerse affects of the Garrison Reservoir.
DESCRIPTION OF PROTECTIVE WORKS FOR WILLISTON
You have been furnished copies of our report and detailed drawings of definite construction plans for the protective works which would be required for Williston and the irrigation district units. Since these are quite detailed in nature, I will summarize their main provisions for you.
The low area along the river in front of Williston is an open, largely unoccupied flat ranging in elevation from about 1,810 at the river to 1,845 at the foot of the railroad fill.
A rolled earth fill levee 814 miles long will protect this area and the Great Northern Railway from flooding. As shown on the map, the levee is at most points a half mile from the present limits of residential or commercial areas of the city.
On the east side of town, the levee follows Little Muddy Creek to its mouth at the Missouri River. From that point it runs westward through an undeveloped area made up of river-bottom sloughs, then parallels the Great Northern railroad upstream to the Lewis and Clark Highway Bridge.
The average height of the levee will be slightly less than 20 feet above the lowlands south of Williston. The top of the levee is generally at about the same level as the Great Northern railroad tracks. The lowest point of the tracks, at the station in Williston, is 4 feet lower than the top of levee. The greater part of the city of Williston lies well above the top of the levee and maximum reservoir levels. In reality, the levee projects the low-lying outskirts, and the railroad yards, rather than the city itself.
Foundations soils for the levee have been checked by drill holes along its entire length. The foundation is very similar to the soils on which hundreds of miles of levee have been built on the lower Missouri and the Mississippi Rivers. The levee itself is designed and will be built with all the essential features which have been developed and tested by years of experience on the Mississippi, and more recently on the lower Missouri.
At the few points where the levee will be subjected to direct attack by the river, the levee slope will be protected by rock riprap. A gravel surfaced patrol road on its crown and another at the landside toe will provide easy access for maintenance, operation, and frequent inspection of the levee.
Vertical drains at the landslide toe of the levee will be provided to prevent the buildup of underground water pressure which sometimes have caused sand boils behind levees.
The protection would not be complete without provisions for disposal of runoff from rains or snowmelt, and provisions for insuring continuous discharge from the sanitary sewer system of the city.
Williston is situated on a crest of high ground which divides the surface runoff into one part which flows into Muddy Creek, and another which flows into the sloughs immediately adjacent to the city on the south. From these sloughs the surface water ultimately finds its way to the river.
During low stages of the reservoir, surface water will pass by gravity flow through gated culverts into Muddy Creek or the river. At peak reservoir stages, the runoff will be handled by two pumping plants-one for the Muddy Creek watershed, one for the area which drains into the river bottom.
The Muddy Creek pumping station will have a capacity of 5,000 gallons per minute. For short periods of time the rate of surface runoff will exceed the capacity of the pumps. This temporary excess of water will be stored within the banks of this (refer to map) loop of Muddy Creek, which will be cut off from the present course of the creek by the levee. This temporary ponding permits a substantial savings in pumping station costs.
Storm runoff from the south and west part of Williston, and from Sand Creek to the west, will continue to flow into the river-bottom sloughs exactly as at present. From these sloughs the water will either flow by gravity, or will be pumped over the levee, depending on river stages. A pumping plant with a capacity of 75,000 gallons per minute will be provided for this drainage area. The plant makes use of the existing ponding areas to absorb the difference between peak runoff rates and the steady capacity of the pumps. These existing ponds have sufficient storage capacity within their banks for storms which can be expected to occur year in and year out. During an exceptionally severe rain or snowmelt period, the ponds would for a short period overflow into adjacent lowlands, but without damage to any improvements in the area.
A third pumping plant, located at the present sewer outlet, will be provided to insure continuous disposal of sanitary sewage. In accordance with standard practice, this plant will handle an average flow of 100 gallons per day per capita, with a peak rate of more than three times the average rate. Two electrically driven pumps with a combined capacity of 2,300 gallons per minute will be installed. In addition, a standby gasoline-engine-driven pump will provide the same total capacity for emergency use. The station will be designed to permit future installation of additional pumps to take care of the city's future growth.
The city of Williston will be reimbursed for the cost of a new water supply intake to replace the existing intake which will periodically be flooded. Funds for this purpose will be sufficient for locating the new intake on the Lewis and Clark bridge, where the river course is stable. The funds will also provide for a new raw water supply line from the bridge location to the city's existing water treatment plant.
In short, the plan provides complete protection against flooding by Garrison Reservoir for the developed lowland areas of Williston, and completely protects the railroad which serves the city. It also assures continued operation of the city's storm and sanitary sewer system without any alteration of these facilities within the city itself. The total estimated cost of the proposed protective works for Williston and the railroad is $4,320,000.
DESCRIPTION OF PROTECTIVE WORKS FOR LEWIS AND CLARK UNIT The Lewis and Clark Irrigation District, across the river and upstream from Williston (see map) will be protected by a rolled earth fill levee about 9 miles in length. The area generally ranges between elevation 1,840 at the downstream end and 1,850 at the upstream end. Incidentally, the levee will protect United States Highway No. 85, which crosses the river at the Lewis and Clark bridge about 5 miles upstream from Williston, and a parallel trunk gasline.
Irrigated lands in the district lie at an elevation of 1,850 feet, which is also the maximum level which will be reached normally by the Garrison Reservoir. To protect this area and its irrigation system against seasonal backwater and the effects of aggradation, the levee will be built to an average height of about 15 feet. Details of its design and construction, with one important exception, will be the same as provided for the Williston levee.
The exception is a ground water control system. Although the reservoir and river will be at or about the ground level for only a few days each year, irrigated areas near the river would become water-logged by underground seepage if no
measures were taken to control ground water levels. In irrigated areas, the water table must be kept a minimum of 5 feet below the surface to be sure that crops will not be harmed by waterlogging.
There are several ways in which ground water control can be accomplished. For example, in Holland the Dutch have for many years used systems of ditches and tile drains to intercept ground water as it rises toward the surface from deep sand beds under the cultivated fields. Another method is to intercept the underground water as it seeps horizontally under the levee. For this purpose, a system of deep wells, each equipped with a pump, is located along the levee surrounding the area.
Both types of groundwater control systems have been considered for the Lewis and Clark unit. Comparative studies show the deep well system to be better suited to the underground conditions in this area, which have been explored by many drill holes along the levee line. This type of control system has the additional advantage that it may be installed and operated with no interference whatever to agriculture within the area. Another very great advantage lies in the fact that the system consists of small and wholly independent units, which can and will be installed only as actual need develops. For the Lewis and Clark anit, the estimated final installation will consist of 105 pumped wells, spaced from 400 to 600 feet apart, and having individual capacities from 1,000 to 2,000 gallons per minute. Flow from the wells will be pumped over the levee to the tiver, or if desired by the farmers, it may be used for irrigation.
The Lewis and Clark levee, being closer to the river than the Williston levee, will require proportionately more bank protection. At the upper end of the unit, a stretch of nearly 2 miles of river bank is already protected by riprap. This protection will be repaired and strengthened. New bank protection will be built in the vicinity of the Lewis and Clark bridge.
As in the case of Williston, a pumping plant will be provided to handle surface drainage of the area during those periods when natural gravity flow is not possible. An old channel of the river forms a natural drain and a low area in which peak flows may be ponded temporarily. At the downstream end of this drain, a pumping plant with a capacity of 16,000 gallons per minute will be built. During the growing season, this pumping capacity can keep the temporarily ponded Fater at a level 10 feet below the average ground level of the area, with no damage to crops. In the snowmelt season, the runoff may be greater than during the growing season. In the improbable event that maximum snowmelt runoff should coincide with a high reservoir elevation, the ponded water might rise temporarily about 3 feet higher than during the growing season.
The total estimated construction cost for protection of the Lewis and Clark mit is $3,540,000.
DESCRIPTION OF PROTECTIVE WORKS FOR BUFORD-TRENTON UNIT
The Buford-Trenton Irrigation District lies on the left bank of the Missouri between the Lewis and Clark bridge and the mouth of the Yellowstone River. The bends of the Missouri divide the district into four units. Of these, only the East Bottom will be affected by backwater from peak reservoir levels, or by the results of aggradation which mạy occur within the predictable future. General elevations in this unit vary between 1,850 and 1,860. Protection of the East Bottom will be accomplished by construction of 10 miles of levee of the same type already described. As shown by the map, the levee begins at a point 1 mile Upstream from the Lewis and Clark bridge, follows the left bank of the river apstream to a point near the town of Trenton, then doubles back along a tributary known as Pointed Wood Creek, ending at the point where this creek enters the flood plain.
Ground-water control will be accomplished by a system of deep wells such as is proposed for the Lewis and Clark unit. The well system will be added as need for it develops, and may reach an estimated total of 94 wells.
At several locations in the Buford-Trenton district, parts of the present irrigation-canal system are so near the river that the canal is actively threatened by erosion of the riverbanks. Some sections of the system have been destroyed by bank eutting, and have been reconstructed. In areas where the present canals are too close to the river, they will be relocated in a more secure position back of the new levee. For increased security, rock protection will be placed on the riterbank in two areas where bank cutting has been active. One of these areas is at the east side of the unit, where more than 2 miles of the bank will be ripFapped. The other area, about 14 miles long, is on the south side.
In addition to the necessary relocations of the irrigation canal, the protection system includes a siphon at the point where the main canal crosses Painted Wood Creek, and a gated inlet structure to carry the canal through the levee into the protected area.
The principal surface-drainage problem of the East Bottom unit will be taken care of by a diversion channel for Painted Wood Creek, and the parallel levee already mentioned which will prevent this creek from discharging into the protected area. Surface runoff originating within th area itself will flow through existing drainage ditches to a gated culvert and pumping plant at the east side of the area. The plant will have a capacity of 15,000 gallons per minute, which is sufficient to keep temporary ponding below levels at which crop damage would occur.
The total estimated construction cost of the protective works for the East Bottom unit of the Lewis and Clark Irrigation District amounts to $4,630,000.
POSSIBLE FUTURE MODIFICATION
As I have already told you, it appears that there will be some tendency for aggradation by silting in the backwater reach at the head of Garrison Reservoir. We do not expect this will affect water elevations in the Williston vicinity, beyond what our proposed plans provide for, for a very long time. However, since we must consider potentialities of eventual trouble, the works are designed with a view of possible enlargement. In normal consideration of a project such as this, I would have reported on the works described and ended my testimony at that point. The problem at Williston has, however, been the subject of such controversy and exaggerated claims of engineering impossibility that I feel compelled to describe the consideration we have given to adverse potentials. We already have definite programs for continued study of the river by outstanding hydraulic and river-sediment specialists, plans for further analyses of the situation including possible hydraulic model studies, and a specific program of periodic surveys to collect actual data, as the reservoir is filled, on any actual tendencies toward aggradation which may show up. Also, we know that if any serious trending tendencies toward aggradation do show up, we can counteract any adverse effects by measures such as channel training, periodic channel dredg. ing (which was successful in handling a problem on the Colorado River), and control of river-bottoms vegetation. We propose to utilize any or all of these measures, as they may be appropriate, if they are required.
For conservatism in appraising the complete adequacy of protection which can be provided in the Williston vicinity, we have also prepared an estimate of an upper limit of water levels which might occur at the head of Garrison Reservoir for a so-called condition of “possible advanced aggradation" which we think may be possible as an extreme, but really consider quite unlikely. These water levels developed for "possible future aggradation" are used on the basis of grades for a possible future plan of levees which might ultimately be necessary. You will note that our expert consultants believe, as we in the corps do, that the allowances in these estimates are adequate for any future period which it is reasonable to consider at this time.
The protective systems for Williston, Lewis and Clark, and the Buford-Trenton area, which I have already described, have been designed and will be built in such a way that the height of the levees can be increased if the necessity should ever arise.
Sufficient base width will be provided to allow for raising the levees without relocation or major reconstruction of the interior drainage or ground water control facilities.
The disposition of river sediments outside the levees will partially block the entrance of underground seepage water into the area, offsetting the increased flow which would otherwise occur because of higher river levels. Consequently no increase in the number of wells is probable, although they would be operated for longer periods each year.
If it should become necessary to raise the levees originally built, the system would at the same time be extended upstream. Such an extension would consist of levees, ground water control systems, and pomping plants to dispose of surface runoff, all of the same type to be used for the basic protective works. At this time, the question as to how far upstream the system might be extended is purely hypothetical. But in order to be sure that such an extension is feasible if it should be required, we have gone all the way and have laid out a protective system for the entire Buford-Trenton district.