Using artificial tracers to study water losses of ephemeral floods in small arid streams

Tracer techniques were used to study infiltration losses into a dry wadi bed. In order not to be fully dependent on rarely occurring natural flood events, an artificial flash flood was studied in a small arid stream channel, Nahal Shahmon, Israel. A reservoir was built, filled with water (550 m³) and breached artificially. Three different artificial tracers were injected at different times during the flood. At two locations downstream surface water samples were taken. The water moving within the alluvium was also sampled with the help of fluocapteurs distributed at different locations within the alluvial body. The fluocapteurs enabled the different pathways of the two dye tracers downstream to be identified and the maximum depth of infiltration to be approximated. This sampling technique is promising for future studies in arid rivers, since fluocapteurs can stay for a long time without any maintenance. Towards the end of flow, exfiltration from the channel alluvium was observed. The interplay between surface and exfiltrating water is described by a simple model.