Hydrological assessment and management implications for the ancient Nabataean flood control system in Petra, Jordan

Evaluating the function and effectiveness of the Nabatean flash flood management system in Petra requires both insight into the nature and extent of the system as well as its hydrological information. Studies of runoff and flooding in semi-arid mountainous regions with high potential for flash floods, such as Petra, can be limited by the lack of any runoff measurements as well as low-resolution rainfall and terrain data. Wadi Hremiyyeh is a small catchment that flows into the Treasury Plaza and is responsible for much of the flooding that occurs there. Half meter spatial-resolution digital elevation model (DEM) was built for this catchment using unmanned aerial vehicles (UAV) surveying, which was useful in determining the exact sites of terraces built by the Nabataeans for flood management. Rainfall data from the nearby Wadi Musa station was supplemented with a new station installed through this project for continuous precipitation measurements at the site. New water level meters specifically designed for that purpose were installed within the main channel. Four of the ancient Nabataean and post Nabataean check dams were restored. Data collected from the 2019–2020 rainy season created an understanding of the rain-runoff conditions at the site and was utilized in constructing and calibrating hydrological models using HEC-HMS and HEC-RAS software. The function and the effectiveness of the rebuilt terraces were evaluated. The models suggest that terraces are effective at delaying the flood peak time (up to 25-minute delay for an 18 dam setup) and at reducing the actual amount of water arriving downstream (13.5% volume reduction). Similar results can be observed for lower frequency flood analysis, in which the models also show effectiveness of these interventions. Modeling of a large dam, rather than the smaller terraces and check dams, shows that such an intervention would result in a reduction of 30.5% in peak flow but a delay of the peak of merely 14 min. While Petra was the venue for this work, its techniques and suggested parameters are applicable to cases of similar arid and semi-arid mountainous regions that are subjected to flash floods.