Progress report of investigations of irrigation problems of Lower Moapa Valley, November 1944

PROGRESS REPORT* OF INVESTIGATIONS OF IRRIGATION PROBLEMS OF LOWER MOAPA VALLEY November, 1944 At the request of the Moapa Valley Soil Conservation District and the Muddy Valley Irrigation Company, the Soil Conservation Service has been, and is now, conducting investigations of the opportunities for the more adequate utilization of land and water resources of the Valley. Current considerations of program procedure and construction necessitates this progress report. Certain early decisions by the Muddy Valley Irrigation Company are essential to further progress in the investigations. General Problem The need for storage of excess winter water for use during the deficient summer period has long been recognized. Likewise there has been general recognition of the need for improved distribution canals which will more efficiently deliver the available water. The location and design capacity of rehabilitated or new canals is in degree dependent upon the location of storage facilities. Various studies1/ have been made of storage opportunities and the decision now rests between the White Narrows and Bowman sites, or a combination of the two. Exhaustive investigations of the White Narrows site and cost estimates have been made by the U. S. Indian Service. Initial studies have been made of the Bowman site by the Soil Conservation Service. Factors which should influence the site selection are: Comparative total volume of storage. Comparative cost of storage per acre foot. Comparative cost of operation and maintenance per acre foot. Comparative rate of sedimentation. Possible source of domestic water. Flood control aspects. Structural feasibility of both sites. It is not the purpose of this report to make these comparisons, but rather to present certain basic information about Lower Moapa Valley soil and water resources, and incidentally some preliminary information about the so-called Bowman storage site. *Prepared by Ellis L. Hatt and D. A. Williams, Soil Conservation Service 1/ Report by King and Malone, 1928. Biennial Report of State Engineer, 1940. Reports by U. S. Indian Service. Preliminary Studies by U. S. Bureau of Reclamation. #2 ? Progress Report Irrigable Lands The gross area1/ of irrigable lands in Lower Moapa Valley is approximately 4200 acres. The net area has not been tabulated but will probably not exceed 3700 acres. Water Requirements Based on the land use capability of the lands in Lower Moapa Valley it is estimated that the following crops will be grown and that their irrigation requirements will be approximately as shown: Irrigation Water Requirement It is further estimated that, due to double cropping practices, the actual acres irrigated will be approximately 82% of the crop acres irrigated and that the above mentioned crops will occupy the following percentages of the crop acres: Young alfalfa or comparable legume - 13% Mature alfalfa or pasture - 38% Grain - 25% Sorghum or corn - 12% Truck - 12% A weighted average irrigation water requirement per actual acre irrigated under such a cropping system would be 5.5 acre feet. The estimated monthly distribution of this annual irrigation requirement is shown in Schedule II attached. Water Resources The average flow2/ of Muddy River, as measured at the Home Ranch during the period May 1 to October 1, is about 38 c.f.s. The average flow during the winter months is about 43 c.f.s. These streamflow figures were used in the analysis included in this progress report. The decreed flow between the point of measurement and the source of supply is 4.56 c.f.s. in the summer and 3.21 c.f.s. in the winter while the estimated transportation loss between these points in 3.0 c.f.s. in the summer and 2 c.f.s. in the winter. The average flow, without deducting Indian rights, available at Wells Siding is 30.44 c.f.s. in the summer and 37.79 c.f.s. in the winter. l/ "Better Land Use in Moapa Valley" March, 1944 by Soil Conservation Service. 2/ Biennial Report of State Engineer, 1940. Crop Winter Summer Total Young alfalfa or comparable legumes 2.1 3.5 5.6 A.F. Mature alfalfa and pasture 2.8 3.9 6.7 A.F. Grain 1.8 0.5 2.3 A.F. Sorghum and com - 2.7 2.7 A.F. Truck 2.2 0.7 2.9 A.F. #3 ? Progress Report It has been estimated that, following a possible change in the decree for Indian rights, approximately 4 acre feet per acre (net duty-return flow considered) for 600 acres of Indian lands may be deducted from the annual quantity available to Lower Moapa Valley. The theoretical stream flow by months has been computed on the basis of the above figures, using monthly estimates for the Indian use. See Schedule I attached. Water Supply Improvement From the standpoint of the Muddy Valley Irrigation Company there are two ways to improve the supply of water available for irrigation. The first method is through the storage of unused winter water for summer use. The other method consists of revision and/or lining of the distribution system for the purpose of saving some of the water which is now lost in seepage from canals and laterals. Schedule IX attached has been prepared to show the acreages of land which can be adequately irrigated under the conditions set forth as a result of undertaking various degrees of each means of water supply improvement. Schedule II and Schedule VII provide examples of the method used in computing the results shown in Schedule IX. To obtain the acreages irrigable with distribution losses less than the 30% used in the examples, the water thus saved was considered as being delivered to additional acres at the established duty of 5.5 acre feet per acre. Little definite information is available relative to the actual water losses resulting from the use of the present irrigation distribution system. Likewise experimental results are required for accurate establishment of the rates of loss which might be expected from unlined canals located in the soils of Lower Moapa Valley. Data on losses from canals lined with selected available native materials is another unknown at this time. Rates of water loss used in Schedule IX are purely estimates. Referring to Schedule IX attention is directed to the fact that a small increase in the amount of storage results in considerable increase in the irrigable area up to a certain point, whereupon the rate of acreage increase becomes much less. It is almost certain also, that under the existing physical conditions that a relatively small amount of storage can be secured at a lower cost per acre foot than a relatively large quantity can. It is also worth noting that improvements in the distribution system are shown as increasing the irrigable acreage in a more spectacular manner than the construction of very large storage reservoirs. The final selection of a water supply improvement program should be based upon a thorough consideration of the total soil and water resources of the lower valley. The unit cost (per acre) of total development should be compared to the unit costs (per acre) of various degrees of development. Various phases of development should likewise be evaluated and scheduled with due consideration for comparative benefits per dollar of annual cost. #3a ? Progress Report SCHEDULE I Computation of Net Stream Flow At Wells Siding Dam By Months Month 1/ Stream Flow at Gage Acre Feet Deductions Between Gage & Wells Siding Net Stream Flow at Wells Siding Acre Feet 1/ Decreed right Between Gage & Wells Siding Not including Indian Acre Feet 2/ Estimated Indian requirement 1/ Estimated Transportation Loss between Gage & Wells Siding Acre Feet % total Ac. Ft. October 2643 197 7 168 123 2155 November 2558 191 5 121 119 2127 December S642 197 3 72 123 2250 January 264S 197 3 72 123 2250 February 2386 178 4 98 110 2000 March 2643 197 8 193 123 2130 April 2558 191 10 240 119 2008 May 2336 280 11 264 184 1608 June 2261 271 11 263 179 1548 July 2335 280 14 335 184 1536 August 2335 280 14 335 184 1536 September 2261 271 10 239 179 1572 Total 29600 2730 100 2400 1750 22720 1/ From Biennial Report of Nevada State Engineer, 1940 2/ Based on estimated monthly distribution of annual net duty of 4 acre feet per acre, for 600 acres. The actual monthly amount will depend upon storage and irrigation practices pursued on the Moapa Indian Reservation. SCHEDULE II A Comparison By Months Between Stream Flow At Wells Siding Dam and Total Water Requirements For the Irrigation of 1504 Acres4/ Month 1/ Stream Flow At Wells Siding Dam Acre Feet 2/ Total Requirements Amounts Available For Storage Acre Feet Amounts to be Withdrawn From Storage Acre Feet % Total Unit Ac. Ft./Ac Monthly Total Acre Feet October 2155 8 0, .629 945 1210 November 2127 5 0, .393 591 1536 December 2250 3 0, .236 354 1896 January 2250 3 0. .236 354 1896 February 2000 5 0, .393 591 1409 March 2130 10 0, .785 1181 949 April 2008 12 0, 943 1418 590 May 1608 10 0. .785 1181 427 June 1548 10 0, .786 1182 366 July 1536 13 1, ,021 1536 - August 1536 13 1. .021 1536 -- September 1572 8 0. .629 945 627 Totals 22780 100 7, .857 11814 10906 1/ From Schedule I 2/ Total requirement consists of an estimated annual duty of 5.5 acre feet per acre required at the farm headgate plus a 30% allowance for losses in the project's distribution system. 4/ Maximum acreage irrigable without storage. SCHEDULE VII A Comparison By Months Between Stream Flow At Wells Siding Dam and Total Water Requirements For the Irrigation of 2700 Acres 1/ Stream Flow At Wells 2/ Total Requirements Amounts Available Amounts to be Withdrawn Month Siding Dam Acre Feet % Total Unit Ac. Ft/Ac. Monthly Total Acre Feet For Storage Acre Feet From Storage Acre Feet October 2155 8 0.629 1697 458 November 2127 5 0.393 1061 1066 December 2250 3 0.236 636 1614 January 2250 3 0.236 636 1614 February 2000 5 0.393 1061 939 March 2130 10 0.785 2121 9 April 2008 12 0.943 2545 537 May 1608 10 0.785 2122 514 June 1548 10 0.786 2122 574 July 1536 13 1.021 2758 1222 August 1536 13 1.021 2758 1222 September 1572 8 0.629 1697 125 Totals 22720 100 7.857 21214 5700 4194 3/ 1/ From Schedule I 2/ Total requirement consists of an estimated annual duty of 5.5 acre feet per acre required at the farm headgate plus a 30% allowance for distribution losses. 3/ Approximately 1500 acre feet available annually for all losses in connection with storage. If 200 acre feet is allowed for loss in transportation from Wells Siding to point of storage and 200 acre feet is allowed for evaporation and seepage loss from the reservoir while it is filling, then approximately 5300 acre feet of storage capacity is indicated as necessary for ultimate development of all the Muddy Valley Irrigation Company's water resources. SCHEDULE IX Total Acreage Which Can Be Adequately Irrigated Condition of Distribution System No Storage .600 A. F. Storage 1/ .1200 A. F. Storage 2/ .2800 A. F. Storage 3/ .4100 A.F. Storage 4/ .5300 A.F. Storage 5/ 1. As is: (30% allowance for distribution losses) 1505 1750 2000 2275 2500 2700 11. Revised unlined Ditch (15% allowance for distribution losses) 1825 2125 2430 2760 3033 3280 III. Revised - lined Main Canals only. (6% allowance for distribution losses) 2020 2350 2685 3055 3335 3625 IV. Revised - all canals lined. (3% allowances for distribution losses) 2085 2425 2770 3150 3465 3740 l/ 100 acre feet ia allowed for annual reservoir loss. 160 acre feet is allowed for annual reservoir loss. 3/ 670 acre feet is allowed for annual reservoir loss. 940 acre feet is allowed for annual reservoir loss. 5/ 1500 acre feet is allowed for annual reservoir loss. 5300 acre feet is storage capacity indicated as necessary for utilization of all lower valley water resources. Storage Possibilities of Bowman Reservoir A survey now in progress has found the present capacity of this reservoir to be 1380 acre feet. It appears that a volume of between 2500 and 3000 acre feet could be stored in Bowman Reservoir and adjacent basins by raising the existing dam and spillway approximately ten (10) feet. Figures from the current incomplete surveys indicate that more than 4000 acre feet could be stored at this site by raising the water level twenty (20) feet above the existing spillway elevation The present capacity can be attained with no additional construction. Adjustment in a right-of-way easement is required in order to legalize a change in use of the reservoir. The existing outlet structure (a 12" diameter corrugated metal pipe) is rather small, but its replacement is hardly justified unless a larger capacity reservoir is contemplated. A ten (10) foot raise in the maximum Bowman Reservoir water surface would involve: 1. The placing of approximately 80,000 cubic yards of fill. 2. The construction of a higher overflow addition to the existing Bowman spillway. 3. The construction of a new low gradient channel from Wells Siding Diversion to the reservoir. The installation of automatic release gates five feet high in the primary spillway of the Wells Siding diversion dam. 5. The installation of the necessary facilities for the prevention and/or correction of the seepage problem below Bowman Dam. 6. The provision of additional outlet capacity at Bowman Reservoir. Referring to Schedule IX it is seen that a development of this size would provide year around water for from 2200 to 3100 acres of land depending upon amount of water lost through canal seepage. Increases in Bowman Reservoir's maximum water surface in excess of approximately ten (10) feet will require items of construction corresponding to each of the six listed above, plus a more radical alteration or replacement of the Muddy River diversion structure and a relocation or raising of some of the Union Pacific railroad grade. It is obvious that the use of this reservoir at its present capacity would be decidedly advantageous and could be attained at practically no cost. The proximity of this site to the lend to be irrigated is favorable from the standpoint of operation and maintenance. The off-stream location of the site is favorable from the standpoint of reduced siltation. Bowman Reservoir would serve as a possible source of domestic water close to the point of use. The value of Bowman Reservoir for flood protection is minor, when floods of the magnitude of the 1938 one are considered. As stated elsewhere in this report, additional information is needed on the cost and engineering feasibility of each of the construction items mentioned Above, before any final evaluation can be made of Bowman Reservoir's storage potentialities. Conclusions to Date 1. There is ample winter water available for storage which, when used to supplement summer flow, would provide a full years supply for 2700 to 3740 Acres of land depending upon the condition of the irrigation distribution system. 2. There are approximately 3700 acres of desirable irrigable land in Lower Moapa Valley. 3. The possibilities of storing water in the Bowman reservoir at a reasonable cost warrant giving due consideration to this site. Further studies of engineering feasibility and cost are required for a comparison with other available storage sites. 4. Immediate construction of a permanent character on the distribution system should be based on a general plan of development with due consideration to all storage opportunities. 5. The present storage capacity of Bowman Reservoir should be utilized for irrigation purposes as a means of supplementing and regulating low and fluctuating summer flows. Recommendations 1. It is recommended that no further work of a permanent character be done on the east side canal now under construction between Wells Siding and the Bowman Reservoir until a decision has been reached by the Muddy Valley Irrigation Company on the future use of the Bowman reservoir for the storage of irrigation water. 2. It is recommended that the East Side canal below Bowman Reservoir be so located and rehabilitated that it can be used for water from this reservoir. 3. It is recommended that no canal lining be undertaken at this time except where the need, location and capacity are definitely known. 4. It is recommended that surveys, now in progress by the Soil Conservation Service, be limited at this time to: a. Completion of horizontal and vertical controls essential to the determination of canal locations. b. Preparation of a general plan for the distribution system based on the possible use of Bowman reservoir. Such a plan should not eliminate the possibility of some ultimate storage at White Narrows. c. Detailed location and plans of construction for work of immediate concern under the A.A.A. program.