Water management problems in a karst flood-prone endorheic basin

In this note, a case history of improper water management in an endorheic karst basin is described with specific reference to the effect of treated wastewater on the functioning of drainage receptors. The basin is the Asso Torrent basin (Apulia region, Italy), crossed by a dendritic channel system, tributary of a set of swallow holes. The discharge into the channels of effluents deriving from sewage treatment plants (STPs) was designed about 30 years ago to increase recharge for the main regional groundwater system, a deep karstic limestone aquifer subjected to seawater intrusion. However, during this time, number and magnitude of the flood events have increased, with repeated damages to urban and rural areas. Floods depend on several causes, whose identification has required hydrological-geomorphological study, the evaluation of runoff, and the assessment of the contaminant load of the STP effluents. The results of the runoff model suggest the inability to drain storm events even in absence of clogging phenomena. Four out of five STPs are undersized and, especially in summer, discharge larger amounts of suspended solids and nutrients, thus increasing the clogging of the swallow holes. In addition, increasing of intense rain events has exacerbated the problem. As a whole, such issues confirm the necessity to skip the old water paradigms based on the assumption of stationarity of the hydrologic variables (i.e., rainfall and rain intensity) and the building of centralized water infrastructures. Examining the site-specific issues, insights are gained that may help avoid unpleasant environmental consequences in similar hydro-geomorphological settings.