A policy brief recently released by the AfriWatSan team at the Université Cheikh Anta Diop of Dakar provides new information on the hydrological impacts of extreme rainfalls.
Indeed, new observations recorded in the AfriWatSan urban monitoring facility in the Thiaroye and Keur Massar suburb of Dakar show how extreme rainfalls flush faecal pollutants from septic tanks into shallow groundwater.
High-frequency observations of groundwater levels and daily rainfall over the last 4 years highlight the importance of heavy rainfalls in generating groundwater recharge indicated by sharp rises in water tables to heavy rainfall events.
New evidence from the AfriWatSan urban observatory in the Thiaroye/Keur Massar suburb of Dakar shows how extreme rainfalls events lead to episodic flushing of faecal pollutants from septic tanks to the underlying shallow groundwater flowing in the Quaternary sands of the Cap-Vert peninsula. Previous research has traced the source of nitrate in shallow groundwater to faecal sources, recharge to heavy rainfalls, and demonstrated a statistically significant association between the density of septic tanks and nitrate concentrations shallow in groundwater.
The observations presented in the attached brief provide for the first time direct, definitive evidence of how extreme, heavy rainfalls transport faecal pollutants from septic tanks to shallow groundwater.