Estimating Hydraulic Properties of Volcanic Aquifers Using Constant‐Rate and Variable‐Rate Aquifer Tests¹

Abstract

In recent years the ground‐water demand of the population of the island of Maui, Hawaii, has significantly increased. To ensure prudent management of the ground‐water resources, an improved understanding of ground‐water flow systems is needed. At present, large‐scale estimations of aquifer properties are lacking for Maui. Seven analytical methods using constant‐rate and variable‐rate withdrawals for single wells provide an estimate of hydraulic conductivity and transmissivity for 103 wells in central Maui. Methods based on constant‐rate tests, although not widely used on Maui, offer reasonable estimates. Step‐drawdown tests, which are more abundantly used than other tests, provide similar estimates as constant‐rate tests. A numerical model validates the suitability of analytical solutions for step‐drawdown tests and additionally provides an estimate of storage parameters. The results show that hydraulic conductivity is log‐normally distributed and that for dike‐free volcanic rocks it ranges over several orders of magnitude from 1 to 2,500 m/d. The arithmetic mean, geometric mean, and median values of hydraulic conductivity are respectively 520, 280, and 370 m/d for basalt and 80, 50, and 30 m/d for sediment. A geostatistical approach using ordinary kriging yields a prediction of hydraulic conductivity on a larger scale. Overall, the results are in agreement with values published for other Hawaiian islands.

Noble gases and coupled heat/fluid flow modeling for evaluating hydrogeologic conditions of volcanic island aquifers

“…These structures are generally less permeable than the basalts they intrude. Saturated hydraulic conductivity values reported for dike complexes of Oahu were as much as four orders of magnitude lower than for dike-free zones (Hunt, 1996;Rotzoll et al, 2007). Ingebritsen and Scholl (1993) reported much lower hydraulic conductivity for deeply buried (>1 km) basalts of the Kilauea volcanic rift zone on Hawaii compared to surficial basalt flows, attributed to either pervasive intrusion of less-permeable dikes and (or) hydrothermal alteration.…”

Estimating hydraulic properties of coastal aquifers using wave setup

“…(4) and (5) using the corresponding setup periods for the SWELL subset and those identified in the spectral analysis. The results are listed in Table 2 and compared with results for the same study area using aquifer tests (Rotzoll et al, 2007), a specific-capacity relationship , and tides . Hydraulic diffusivity estimated from the decomposed setup signal yields identical results for g S and g V , with an effective diffusivity of 2.3 · 10 7 m 2 /d.…”

“…Aquifer tests Rotzoll et al (2007) 310 Specific capacity 423 Ocean tides 1.6 · 10 7 350 2.9 · 10 7 655 2.3 · 10 7 500 a Estimated from diffusivity using S of 0.04 and b of 1.8 km. b D* -arithmetic mean of D amp and D pha .…”

“…A reasonable aquifer depth is 1800 m below mean sea level, which coincides with a seismic velocity unconformity detected on Oahu (Furumoto et al, 1970). Rotzoll et al (2007) analyzed 238 aquifer tests and estimated a mean hydraulic conductivity of 310 m/d for the Honomanu/Kula basalts. Using an empirical relationship between hydraulic conductivity and specific-capacity, Rotzoll and El-Kadi (2008) estimated a mean hydraulic conductivity of 423 m/d for 218 wells in Maui's dike-free flank lavas.…”

“…A simple numerical groundwater flow model was used to evaluate the accuracy of the estimated hydraulic parameters. The results were compared with aquifer parameters estimated for the same study area using aquifer tests (Rotzoll et al, 2007), specific-capacity (Rotzoll and ElKadi, 2008), and tides .…”