Technical Memorandum Report No. 72
Macrodispersivity of Selected Hawaii Basaltic Aquifers
L. Stephen Lau and Ben E. Ishii
Longitudinal dispersivity was evaluated in terms of local transverse dispersivity for the permeable, thin layered Hawaiian basaltic aquifers on the basis of Gelhar’s macrodispersion theories and photo logs and electrical resistivity logs for several wells on Oahu, Hawaii. Transverse dispersivity was evaluated on the basis of salinity-depth curves of thick, freshwater lenses on Oahu and an assumed flow pattern parallel to the freshwater-saltwater interface. The longitudinal dispersivity values based on electrical resistivity logs involved less subjectivity and are more reliable than those based on photo logs. The longitudinal dispersivity values are on the order of magnitude of tens to hundreds of feet, whereas the transverse dispersivity values are on the order of tenths of feet. Geographic variation appeared to be considerable among the evaluated longitudinal dispersivity values but limited for transverse dispersivity values. Vertical variation of hydraulic conductivity in Hawaii layered basalt followed the log-normal distribution. Further, the correlation length of this space series was shown to linearly related to the average layer thickness.