Nahal Shahmon, a small ephemeral stream channel in the southern Negev, drains an area of about 4 km2 towards the town of Eilat into the Red Sea. Bare outcrops of magmatic and metamorphic rocks dominate the catchment. The climate is hyperarid with mean annual rainfall below 50 mm. Upon exiting the mountains, the channel is confined for about 250 m with a steep slope. This section has been used as a dirt road and was chosen for an artificial flood experiment. A reservoir was built, filled with water (550 m3) and breached artificially. At different times three artificial tracers were injected about 10 m downstream the breach (Lange et al, 1998). Approximately five seconds after the breach the flood passed the site of injection and Sulforhodamine (SRB, 400 g) was injected directly into the wave front. Uranine (UR, 400 g) was injected 45 s later and salt (NaCl, 15 kg) was injected close to peak discharge after another 50 s.
 |
Surface water samples were taken at two locations. Sampling site 1 was located about 120 m downstream the dam; had to be taken near the left bank. Sampling site 2 was located about 240 m downstream the dam; here the location of sampling was close to the right bank. The infiltrating water was sampled directly within the unsaturated zone. This was done by fluocapteurs placed about 20 cm beneath the channel surface at several locations. Within two trenches depths up to 1.5 m were reached. Fluocapteurs consist of small steel mesh bags containing approximately 10 g of adsorptive charcoal. The fluorescence tracers in the infiltrating water were adsorbed by the charcoal and kept inside the samples. After the event the fluocapteurs were recovered and analysed for the adsorbed tracers. |