The abandoned Roman/Early Islamic city of Resafa in the Syrian desert steppe was supplied with drinking water by an elaborate floodwater harvesting system. This paper investigates its construction, reliability and chronology. Previous excavations showed that the system consisted of a dam that blocked a wadi adjoining the enclosed city and channeled retained floodwater to large subsurface cisterns. Aerial photos from the early 20th century suggest that additionally embankments were part of the system. Physical evidence of such constructions is largely lacking nowadays.
The reliability analysis of the floodwater system is conducted by applying a curve-number-based rainfall-runoff model driven by current satellite rainfall estimates. Flow pattern analysis is used to assess the probable effects of the assumed embankments on flood behavior by applying the hydraulic module of the Caesar-Lisflood model.
We show that the system would be reliable under present conditions and probably also functioned when the system was in operation. Furthermore, it is shown that the floodwater harvesting system most likely consisted of a several hundred meter long embankment system.