WRRC Technical Reports

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    WRRCTR No.41 Electrodialysis for Desalting Hawaiian Brackish Ground Water: A Field Study
    (Water Resources Research Center, University of Hawaii at Manoa, 1970-07) Lau, L. Stephen ; Chou, James C.S.
    A field study was made to evaluate the applicability and problems of desalting brackish ground water from basaltic and reef limestone aquifers in Honolulu, Hawaii with the electrodialysis process. The three-week study indicated that the brackish water at both sites was upgraded to potable quality and the rejection of ionized salts was above 80 percent. No pretreatment was necessary. Both the average production and rejection rates were about 420 gpd. An economic evaluation was not determinable from the short-term results.
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    WRRCTR No.42 Instantaneous Unit Hydrograph Analysis of Hawaiian Small Watersheds
    (Water Resources Research Center, University of Hawaii at Manoa, 1970-08) Wang, Ru-Yih ; Wu, I-Pai ; Lau, L. Stephen
    The analysis of about 240 flood hydrographs of 29 small watersheds on the island of Oahu, Hawaii, shows some unique hydrologic characteristics. A typical Hawaiian small watershed has a small area, flash peak, short time to peak, and small recession constant. Most of the hydrographs have the typical shape of a steep triangle. Based on statistical analysis of the observed flood hydrographs, a linear relationship has been found between peak discharge and the volume of runoff for each watershed. Because of the similar shape of the semi-dimensionless hydrographs, a unit-hydrograph with uncertain duration can be developed for each small watershed. The duration of such unit hydrographs can be determined by using the S-hydrograph technique with the equilibrium discharge as a criterion and the trial-and-error method utilizing a digital computer. The durations of the unit hydrograph, or the effective rainfall durations for Hawaiian small watersheds, were found to range from 5 minutes ot one hour. A good correlation has been found to exist between effective rainfall duration and the watershed area. Such a short duration unit hydrograph can be used to develop an instantaneous unit hydrograph by using Nash's conceptual model and the method of moments, assuming the effective rainfall is uniformly distributed with respect to time and space. The instantaneous unit hydrgraph for each watershed can then be solved by a computer. The two instantaneous unit hydrograph parameters, Gamma function argument, N, and reservoir storage constant, K, were found to correlate with areas of small watersheds. The instantaneous unit hydrograph of a given ungaged area can be determined by knowing the area of the watershed. The flood hydrograph with a given duration can also be solved by applying the incomplete Gamma function. The superposition characteristics of a linear model can be applied for hydrograph analysis of Hawaiian small watersheds. Hence, the design discharge with certain recurrence years for different engineering purposes can be directly multiplied with the design runoff, which may be obtained with the reference of the rainfall depth-frequency-duration charts and soil conditions for certain areas. A hydrograph study using an instantaneous unit hydrograph provides a good approach for hydrologic research since the short duration of effective rainfall is close to the duration caused by an instantaneous burst of rainfall. The study also synthesizes the parametric hydrograph which simplifies hydrograph analysis.
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    WRRCTR No.44 Identification of Irrigation Return Water in the Sub-surface, Phase III: Kahuku, Oahu and Kahului and Lahaina, Maui
    (Water Resources Research Center, University of Hawaii at Manoa, 1970-12) Tenorio, Pedro A. ; Young, Reginald H.F. ; Burbank, Nathan C Jr. ; Lau, L. Stephen
    This study continued the joint research effort undertaken by the Water Resources Research Center and the Honolulu Board of Water Supply in 1967 to investigate the physical and chemical characteristics of irrigation return water. Initial work concentrated on the Pearl Harbor-Waipahu area of Oahu. The phases reported herein included both Kahuku Plantation on Oahu and the sugar cane cultivation areas of central and West Maui (Pioneer Mill Co. and Hawaiian Commercail and Sugar Co.). Composite well, spring, and stream samples were taken and analyzed in the laboratory for the following constituents: bicarbonate, calcium, magnesium, phosphate, silica, boron, chloride, nitrate, sodium, potassium, bromide, flouride, sulfate, and total hardness. On the basis of increased index constituents over uncontaminated ground-water sources used to identify the presence of irrigation return water, it is evident, as previously concluded by Visher and Mink (1964), such irrigation return water, is definitely present in the basal water bodies underlying the three study areas. Considerable increases in the nitrate and sulfate indices, especially, and in the bicarbonate and silica indices, as shown by various methods of interpretation of water quality data obtained over a period of approximately two years or exceeding one complete cycle of plainting and harvesting of sugarcane, verify the strong influence of irrigation agricultural practices in altering the overall quality of the basal water sources in the three areas. The basal water quality of the HC&S aquifer is most affected regionally, as well as locally, by the prevailing agricultural practices. The deterioration of the water is dues in part to fertilization and to a greater exten to heavy pumping and recycling of the basal water. Water quality in the Pioneer Mill area parallels that of HC&S, although on a regional basis, the basal water quality, unlike that of the Pioneer Mill area, is not as deteriorated. Local effects of pumping are also especially noticeable in the Pioneer Mill area. Ground-water quality in the Kahuku area shows the obvious presence of irrigation return water indices, but, unlike the two plantations on Maui, the magnitude of the increases relative to uncontaminated water sources is considerably smaller. The effect of fertilization on Kahuku may be considered to be a principal factor in the regional distribution of index constituents with a relatively uniform nitrate distribution throughout. Local effects of pumping are quite pronounced and influence overall increases of indices, indicating that where heavy pumping takes place for irrigation, the increase in index constituents are correspondingly greater.
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    WRRCTR No. 45 Density Logs from Underground Gravity Surveys in Hawaii
    (Water Resources Research Center, University of Hawaii at Manoa, 1971-02) Huber, Richie D. ; Adams, William M.
    The gravity method has been applied in three wells in Hawaii to estimate density and porosity logs. The wells are the Schofield shaft on the island of Oahu, the Kihei #3 shaft on the island of Maui and the Pahala shaft on the island of Hawaii. The method determines the "averaged" density and porosity values for Hawaiian rocks. On Oahu, the density at depth is 2.4 gm/cc and the corresponding porosity is 18 percent. For Maui, the density averages about 2.4 gm/cc and porosity at 17 percent. The Hawaii shaft shows a lower density of 2.0 gm/cc with a correspondingly higher porosity of 27 percent. All these values are based on a grain density of 2.9 gm/cc.
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    WRRCTR No. 4 Development of Deep Monitoring Stations in the Pearl Harbor Ground Water Area, Oahu
    (Water Resources Research Center, University of Hawaii at Manoa, 1967-03) Cox, Doak C. ; Lao, Chester
    Two deep wells, one at Puuloa and the other at Ewa Beach in the Pearl Harbor area were drilled through the thick sedimentary gap into Koolau basalt, and have been readied for multiple-zone recording of water levels and water quality. Plastic pipes were lowered into the wells to selected depths determined by core composition and electric well logs. Gravel and beach sand were used selectively to backfill the wells. Thirteen sampling tubes were installed in the Puuloa well, and seven sampling points were placed in the main well at Ewa Beach. A shallow auxiliary well was also drilled at Ewa Beach. Evidence from preliminary development of the deep aquifer at Ewa Beach indicates the possible existence of a thin layer of fresher water floating on water of nearly seawater composition. Water levels are being monitored in this aquifer and show a tidal efficiency of approximately 15 percent. The smaller sampling tubes are being developed at both sites.
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