Hydrological modelling and the sustainable development of the Hadejia-Nguru Wetlands, Nigeria

Abstract

The Hadejia-Nguru Wetlands produce agricultural, fishing and fuelwood benefits of upto 1277 Naira ha⁻¹ (N1 = US$22, October 1994), over five times the productivity of formal irrigation schemes. The wetlands play a vital role in aquifer recharge. The key is the annual wet season flooding of over 2000 km² in the 1960s and around 1500 km² in the 1970s. A water balance model, utilizing monthly hydrological and meteorological data simulates flood extent and groundwater storage within the wetlands. The model was operated between 1964 and 1987 and was calibrated using observed flood extents ranging from 50 to 3265 km². Subsequently elements were added for dams and irrigation schemes. Results indicate that full implementation of all the schemes constructed or planned would cause flooding to be less than 375 km²for 60% of the time and groundwater storage to fall by over 5500 10⁶ m³. It is possible to define an operating regime for the basin's hydraulic structures which could provide artificial floods and enable a distribution of water between formal irrigation, small scale irrigators, the wetlands and downstream users. This regime would provide assured flooding, of around 1000 km² each year, and a reduced loss of groundwater storage. Such a sustainable development scheme could offset decades of piecemeal development and bring a philosophy which emphasizes water use throughout the basin not just in irrigation in the upper reaches.