The hydrology of the Jordan tributaries (Israel): Hydrographic and isotopic investigation

Abstract

Nahal Dan, Nahal Snir and Nahal Hermon are the three principal tributaries of the Jordan River. All three are spring-fed and appear to derive their discharges from the same regional groundwater aquifer. The behaviour of this aquifer is examined by hydrograph separation and multivariate time-series analysis of discharge and rainfall records, and by investigation of 18O and tritium records. Hydrograph separation gives base-flow recession constants of 11–20 months and in addition N. Snir and N. Hermon show an interflow recession of ∼ 1 month. The dual reservoir system for these two tributaries is confirmed by time-series analysis. 18O data distinguish the different catchments for the springs and support the idea that interflow occurs in the near-surface part of the regional groundwater reservoir. Tritium data illustrate the inhomogeneity of the karstic reservoir. Assuming well-mixed conditions, the difference in behaviour between tritium records for rainfall and the tributaries is used to estimate the age distribution of water in the reservoir. At any time 50% of the storage is less than 1 yr. old and 90% is less than 3 yr. old.