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Rapid urban development and population growth in Palm Beach County, Florida, have been accompanied with the need for additional freshwater withdrawals from the surficial aquifer system. To maintain water quality, County officials protect capture areas and determine zones of transport of municipal supply wells. A multistep process was used to help automate the delineation of wellhead protection areas. A modular ground-water flow model (MODFLOW) Telescopic Mesh Refinement program (MODTMR) was used to construct an embedded flow model and combined with particle tracking to delineate zones of transport to supply wells; model output was coupled with a geographic information system. An embedded flow MODFLOW model was constructed using input and output file data from a preexisting three-dimensional, calibrated model of the surficial aquifer system. Three graphical user interfaces for use with the geographic information software, ArcView, were developed to enhance the telescopic mesh refinement process. These interfaces include AvMODTMR for use with MODTMR; AvHDRD to build MODFLOW river and drain input files from dynamically segmented linear (canals) data sets; and AvWELL Refiner, an interface designed to examine and convert well coverage spatial data layers to a MODFLOW Well package input file. MODPATH (the U.S. Geological Survey particle-tracking postprocessing program) and MODTOOLS (the set of U.S. Geological Survey computer programs to translate MODFLOW and MODPATH output to a geographic information system) were used to map zones of transport. A steady-state, five-layer model of the Boca Raton area was created using the telescopic mesh refinement process and calibrated to average conditions during January 1989 to June 1990. A sensitivity analysis of various model parameters indicates that the model is most sensitive to changes in recharge rates, hydraulic conductivity for layer 1, and leakance for layers 3 and 4 (Biscayne aquifer). Recharge (58 percent); river (canal) leakance (29 percent); and inflow through the northern, western, and southern prescribed flux model boundaries (10 percent) represent the major inflow components. Principal outflow components in the Boca Raton well field area include well discharge (56 percent), river (canal) leakance (27 percent), and water that discharges along the coast (10 percent). A particle-tracking analysis using MODPATH was conducted to better understand well-field ground-water flow patterns and time of travel. MODTOOLS was used to construct zones-of-transport spatial data for municipal supply wells. Porosity estimates were uniformly increased to study the effect of porosity on zones of transport. Where porosity was increased, the size of the zones of transport were shown to decrease.
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The study area lies on the northern flank of theEast Maui Volcano (Haleakala) and covers about129 square miles between the drainage basins ofMaliko Gulch to the west and Makapipi Stream tothe east. About 989 million gallons per day of rain-fall and 176 million gallons per day of fog dripreaches the study area and about 529million gal-lons per day enters the ground-water system asrecharge. Average annual ground-water with-drawal from wells totals only about 3 million gal-lons per day; proposed (as of 1998) additionalwithdrawals total about 18 million gallons per day.Additionally, tunnels and ditches of an extensiveirrigation network directly intercept at least 10 mil-lion gallons per day of ground water.The total amount of average annual stream-flow in gaged stream subbasins upstream of 1,300feet altitude is about 255 million gallons per dayand the total amount of average annual base flow isabout 62 million gallons per day. Six major sur-face-water diversion systems in the study area havediverted an average of 163 million gallons per dayof streamflow (including nearly all base flow ofdiverted streams) for irrigation and domestic sup-ply in central Maui during 1925–97.Fresh ground water is found in two mainforms. West of Keanae Valley, ground-water flowappears to be dominated by a variably saturatedsystem. A saturated zone in the uppermost rockunit, the Kula Volcanics, is separated from a fresh-water lens near sea level by an unsaturated zone inthe underlying Honomanu Basalt. East of KeanaeValley, the ground-water system appears to befully saturated above sea level to altitudes greaterthan 2,000 feet. The total average annual streamflow of gagedstreams west of Keanae Valley is about 140 milliongallons per day at 1,200 feet to 1,300 feet altitude.It is not possible to estimate the total averageannual streamflow at the coast. All of the base flowmeasured in the study area west of Keanae Valleyrepresents ground-water discharge from the high-elevation saturated zone. Total average dailyground-water discharge from the high-elevationsaturated zone upstream of 1,200 feet altitude isgreater than 38 million gallons per day, all of whichis eventually removed from the streams by surface-water diversion systems. Perennial streamflow hasbeen measured at altitudes greater than 3,000 feetin several of the streams. Discharge from the high-elevation saturated zone is persistent even duringperiods of little rainfall. The total average annual streamflow of the gaged streams east of Keanae Valley is about 109million gallons per day at about 1,300 feet altitude. It is not possible to estimate the total average annual streamflow at the coast nor at higher altitudes. All of the base flow measured east of Keanae Valley represents ground-water discharge from the vertically extensive freshwater-lens system. Total average daily ground-water discharge to gaged streams upstream of 1,200 feet altitude is about 27million gallons per day. About 19 million gallons per day of ground water discharges through the Kula and Hana Volcanics between about 500 feet and 1,300 feet altitude in the gaged stream sub-basins. About 13 million gallons per day of this discharge is in Hanawi Stream. The total ground-water discharge above 500 feet altitude in this part of the study area is greater than 56 million gallons per day.
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To determine the reasons for the unusually low runoff in the Concho River basin during the period 1962-68, the physical developments and climatic changes in the basin were identified and related to changes in the regimen of streamflow. Land use, brush infestation, and land-treatment practices have not caused significant changes in the rainfall-runoff relationship. The use of surface water for irrigation has increased very little during the past 70 years, and although the use of ground water for irrigation has greatly increased in the past 25 years, springflow has not been significantly diminished. The base flow of the streams is materially reduced by surface-water irrigation diversions. Diversions for municipal and industrial use have increased rapidly, but these diversions affect only the streamflow downstream from San Angelo. Statistical analyses showed the annual rainfall to be highly variable, with little serial correlation. Records of rainfall during the period 1943-68 are significantly different in character from previous long-term records. The frequency of monthly rainfall equal to or greater than 2.0 inches during the period 1943-68, and especially during the period 1962-68, was significantly less than the long-term averages. Analyses of annual runoff data, adjusted for depletions, show large variations in annual runoff. Coefficients of variation ranged from 0.8 to 1.4, and first-order serial correlations ranged from 0.01 to 0.28. The estimated recurrence interval of the 1962-68 drought is about 200 years. The analyses of rainfall-intensity and runoff data indicate that the basic cause for the relatively low runoff during the period 1962-68 was the lack of high-intensity, long-duration storms rather than any physical changes or agricultural practices in the watershed
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