Evaluation of depression storage in an arid rocky basin using stable isotopes of oxygen and hydrogen

The relationship between the isotopic composition of rainfall and runoff in an arid, bare rock basin is utilized to evaluate the volume of the surface depression storage. The sequential isotopic distribution was measured at about 2 mm in rainfall fractions and in six minute fractions of the corresponding runoff. Two types of storms were identified: (a) rainstorms with a constant isotopic composition along each rain spell and (b) rainstorms with a variable isotopic distribution. A mixing cell model is proposed to assess the percentage of area occupied by temporary depression storage. The isotopic composition of the runoff at the outlet of the basin is assumed to be controlled by the isotopic input of rainfall mixed with the surface detention storage and depression storage. The latter reflects the isotopic composition prevailing in the previous rain spell. Two models are suggested for the two aforementioned rainstorm types. In this paper, only the first model is presented. This model provides the average area and depth of the depression storage from which the average detention volume is computed.