1. Fluid flow processes in the Beppu geothermal system, Japan;Allis;Geothermics,1989
2. Thermal groundwater system of downtown Beppu as inferred from two chemical components;Kikkawa;Reports of Oita Prefecture Hot Spring Research Society,1951
3. On the water leakage between two-layered aquifers illustrated from the observations in the Beppu hot springs;Kikkawa;Japanese Journal of Limnology,1960
4. Bromine and iodine contents of hot spring water under seawater contamination in Beppu;Kikkawa;Reports of Oita Prefecture Hot Spring Research Society,,1964
5. Sea water contamination in the southern hydrothermal area of Beppu;Kikkawa;Reports of Oita Prefecture Hot Spring Research Society,1977