In western Kansas, more than 95 percent of the precipitation on the land surface is evaporated from the soil or is transpired by plants. Seepage of part of the sporadic upland runoff carried by natural drains that traverse the study area and infiltration and percolation of rainfall on the cultivated area during abnormally wet years probably contributes a small amount of recharge to the ground-water reservoir. However, consumptive use of water by natural and cultivated vegetation exceeds normal rainfall during the growing season. Where the moisture deficiency was overcome by irrigation, more water became available to percolate below the root zone into the groundwater reservoir.
Official records of precipitation at Cedar Bluff Dam, Ellis, and Hays (National Weather Service) were supplemented by daily observations at five project stations equipped with wedge-shaped plastic rain gages (fig. 2). Records were kept by volunteer observers including: Mrs. S. Irwin (rain gage 1); Mr. R. Schamel (rain gage 2); Mrs. F. Dinkel (rain gage 3); Mr. J. T. Wanamaker (rain gage 4); and Mr. B. Younger (rain gage 5). Average annual precipitation is less than 23 inches (58 cm), about 75 percent of which normally occurs during the growing season April through September. Deficiencies in annual rainfall at Hays, about 8 miles (13 km) northeast of the district, in 1964, 1966, 1968, and 1970 far exceeded the recorded excess during the alternate years (table 1). Without the additions of water from irrigation , the period of study might have been characterized by a declining water table and diminished base flow in the Smoky Hill River adjacent to the district.
Table 1--Annual precipitation at stations near Cedar Bluff Irrigation District, 1963-71. [U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Data Service, Climatological data, Kansas, Annual Summaries 1963-71.]
|Year||Precipitation at indicated stations, in inches1||Departure from
normal at Hays
|Cedar Bluff Dam||Ellis||Hays|
|1 Inches X 2.54 equals centimeters.
During 1963-71 the annual precipitation at Hays generally exceeded the annual precipitation at Cedar Bluff Dam by several inches. A large part of the rainfall occurred during intense localized convective storms of short duration; therefore, recorded daily values at one station do not necessarily apply to the entire district. However, the apparent increase in precipitation from west to east was also observed at the project stations. The values for annual precipitation used in calculations for this report represent areally weighted averages of values recorded at the dam and at project stations. During 1964-71, annual rainfall ranged from about 17 to 29 inches (43 to 74 cm); the mean was about 22 inches (56 cm).
The quantity of dissolved solids in rainfall is negligible; therefore, increased rainfall normally causes dilution of ground and surface water. During periods of high runoff, calcium and bicarbonate are transported into and through the district from limestone areas to the north, and salts that have accumulated near the land surface throughout the drainage area during drier periods are flushed to the river. The quantity of accumulated salts carried from the district by storm runoff is virtually impossible to measure; therefore, no attempt has been made to describe a total salt balance for the irrigation district.
Data from previous investigations and from adjacent nonirrigated areas during this investigation indicate that the quantity and chemical quality of ground water beneath the district before irrigation varied within a relatively narrow range in response to variations in precipitation. Although the rate of application of irrigation water generally varied inversely with precipitation, the introduction into the system of large volumes of water containing significant quantities of dissolved solids caused progressive changes in the quantity and quality of the ground water that were distinct from those caused by variations in rainfall.
The quantity and rate of application of irrigation water affects the quality of related water supplies as well as the crop response in the irrigated area. For example, a rising water table, local waterlogging of soils, or acceleration of ground-water discharge may indicate excessive applications of water. Reduction of diversions would save water and reduce the volume of potentially pollutant return flow. Conversely, reduction of the quantity of applied water could cause undesirable diminution of sustained low flow in the river, degradation of ground-water quality, increased salinity in stock ponds and other impoundments receiving drainage from the district, and an unfavorable salt balance in the soil.
Deliveries and Consumptive Use
The acreage under irrigation expanded from 2,226 acres (900 ha) in 1963 to 5,897 acres (2,400 ha) in 1971. Diversions to the irrigation canal ranged from 7,146 acre-feet (8.8 hm3) in 1963 to 17,725 acre-feet (21.9 hm3) in 1968 (fig. 4 and table 2). The net input (N) of water delivered to the district is equal to the total diversion from the reservoir (D) minus waste (W) (fig. 2). Waste is water discharged from the end of the canals and laterals to maintain flow throughout the system. Presumably, the waste returns to the river virtually undiminished in quantity and unchanged in quality, but a small part is consumed by plants in the natural wasteways.
Figure 4--Acres irrigated, canal diversions, and average distribution of water per irrigated acre, 1963-71.
Table 2--Distribution and consumption of water in and adjacent to Cedar Bluff Irrigation District, 1963-71.
|D||Diversion to canal||acre-feet||7,146||12,821||12,700||14,273||11,562||17,725||11,016||15,796||13,686|
|N||Net input (D-W)||acre-feet||6,513||11,857||11,509||12,473||10,970||17,096||10,491||15,048||13,179|
|I||Deliveries to farms||acre-feet||2,475||6,145||6,955||7,909||6,546||11,676||6,522||10,767||8,935|
|Pa||Annual rainfall on
|Pe||Effective rainfall on
in irrigated area
R = C - Pe
F = R/D x 100
|Xn||Excess input, Xn = N - R||acre-feet||8,890||10,332||8,695||9,250||11,467||6,529||10,059||7,010|
|Xi||Excess farm deliveries,
Xi = I - R
|Ax||Excess water from irrigated
land,5Ax = Pa + I - C
ratio, CR = N/Xn
|En||Predicted specific conductance
of annual excess
input, En= EiN/Xn,
Ei, specific conductance of irrigation water
centimeter at 25°C
|Ex||Predicted specific conductance
of cumulative excess
input, Ex = ΣEiNn/ΣXn
centimeter at 25°C
|1Monthly water distribution records, U.S. Bureau of Reclamation (written commun.). Acres X 0.4047 equal hectares.
2 Canal and lateral.
3 1966-69, average of rain gages; 1963-65, 1970, 1.3 X rainfall at Cedar Bluff Dam; 1971, average of rainfall at dam and rain gage No. 5. Inches X 2.54 equals centimeters.
4 The part of monthly rainfall during growing season that was equal to or less than consumptive use for each crop.
5 Excess rainfall (Pa - Pe) + excess irrigation water (I-R) = Pa + I - C.
Net input (N) consists of deliveries to farms (1) and losses (L) from the canal and laterals by seepage and evaporation. Evaporative losses from the canal appear to be negligible. Evaporation and transpiration of part of the irrigation water leaves the remainder more highly concentrated. Only slight changes were observed in the specific conductance and concentrations of the ions along the canal during hot weather of the irrigation season; therefore, losses are attributed mainly to seepage.
To estimate the quantity of excess water available for recharge, the average consumptive use (C) of water in the irrigated area was calculated by a slight modification of the method of Blaney and Criddle (1950). The method is based on the tested premise that the consumptive use of water by any crop is determined by temperature, available water, length of the growing season, and of daylight. Monthly consumptive use of water by each crop can be expressed as
U = K f
where U is the monthly consumptive use; K is an experimentally determined coefficient for each crop based on tank and plot studies, and f is the product of the monthly mean temperature and the percent daylight hours that occur in that month. Acreage devoted to each crop was obtained from the annual crop summaries issued by the U.S. Bureau of Reclamation; monthly mean temperatures and date of the first and last frost were obtained from records of the National Weather Service for Hays; the percent daylight hours, definition of the growing season, and crop coefficients applicable to Kansas were taken from Hanson and Meyer (1953). The average consumptive use for the irrigated acreage is shown in table 2 and in figure 4.
The irrigation requirement (R) is defined as consumptive use (C) minus the effective rainfall. The effective rainfall for each year is the cumulative monthly effective rainfall for all crops during the growing season. As used in table 2, the monthly effective rainfall for any crop was the rainfall equal to or less than the consumptive use. If all rainfall during the growing season had been included as effective precipitation, the irrigation requirement would have been negative for several months when heavy rainfall during one or two days exceeded the monthly consumptive use. Calculations are based on the assumption that adequate irrigation water was applied to ensure optimum growth during the growing season; therefore, most of the heavy rainfall would run off the moist soil. Observations during and after heavy convective storms support this assumption, although some of the runoff from the irrigated land undoubtedly infiltrated the soil in adjacent nonirrigated land.
Farm deliveries (1) exceeded the irrigation requirements (R) during 1963-71; therefore, adequate water evidently was available for leaching and recharge in the irrigated area during the growing season. Available recharge from the irrigated land probably is more nearly equal to the excess rainfall for the entire year plus the excess farm deliveries. The excess water from irrigated land (Ax) that is available for recharge is calculated in table 2 from annual rainfall on irrigated land (Pa) plus farm deliveries (1) minus consumptive use (C).
If losses from the canal and laterals (L) represent seepage to the ground-water reservoir, the quantity of water available for recharge as a result of all deliveries of water to the irrigation district would be equal to the net input (N) minus the irrigation requirement (R). The difference is defined as excess input (Xn) in table 2. Thus, concentration of the ions in the infiltrated water depends largely upon the chemical quality of the irrigation water.
The concentrations of dissolved solids in the irrigation water from Cedar Bluff Canal generally increased progressively from year to year (table 3). The specific conductance, in micromhos per centimeter at 25°C, increased from about 800 in 1964 to 980 in 1971. For the purposes of this report, waters are described in terms of the most abundant anion and cation, in me/l (milliequivalents per liter). The percent composition of the calcium-sulfate type water remained relatively constant except for a progressive increase in sulfate and a concomitant decrease in bicarbonate. Bicarbonate and sulfate comprised about 93 percent of the anions. Sulfate and dissolved solids were higher than maximum concentrations recommended for drinking water by the Kansas State Board of Health (1973). Low concentrations of nitrogen and phosphorus indicate that eutrophication of the reservoir is not an immediate problem although the water has a distinct greenish cast during the late summer. The paucity of these nutrients may be responsible for a less than desirable rate of propagation and development of some game fish in the reservoir.
Table 3--Average composition of irrigation water from the Cedar Bluff Canal, 1963-71.
|Concentration, in milligrams per liter|
|Concentration, in milliequivalents per liter|
|Percent total anions and cations|
|* Samples at the gage on the Smoky Hill River at Cedar Bluff Dam.|
According to the classification of the U.S. Department of Agriculture (1954, p. 81), which is based on the specific conductance and sodium-adsorption ratio of the irrigation water (table 3), the water has a low sodium (alkali) hazard and a medium to high salinity hazard for irrigation. According to another classification (Jacobs and Whitney, 1968, p. 17) based on specific conductance and percent soluble sodium, the sodium and salinity hazard for field crops in medium textured soil is low. A moderate amount of leaching is required to prevent accumulation of salt in the soil.
Kansas Geological Survey, Geohydrology
Placed on web Nov. 2012; originally published 1975.
Comments to email@example.com
The URL for this page is http://www.kgs.ku.edu/Publications/Bulletins/CQS1/05_dist.html