TY - JOUR AU - Birkhead, AL AU - Brown, CA AU - Joubert, AR AU - Singh, A AU - Tlou, T PY - 2018/10/31 Y2 - 2024/03/28 TI - The Pongola Floodplain, South Africa – Part 1: Two-dimensional hydrodynamic modelling in support of an environmental flows assessment JF - Water SA JA - WSA VL - 44 IS - 4 October SE - Research paper DO - 10.4314/wsa.v44i4.21 UR - https://watersa.net/article/view/6680 SP - AB - <p>The Pongola Floodplain in the Makhathini Flats is an area of low topographic relief between the 1973-commissioned Jozini Dam,&nbsp;and the Usuthu River which borders Mozambique. The floodplain system is characterised by a complex mosaic of meandering&nbsp;river channels, levees, and floodplains interspersed with pans (or depressions) and wetlands. The landmark 1982 study of the floodplain, <em>Man and the Pongolo Floodplain</em>, suggested a pattern of flows to ‘maintain the floodplain’ based on socio-ecological&nbsp;criteria. Since 1998, however, annual releases have been primarily targeted at the needs of recession agriculture and inundation&nbsp;of the floodplain in the Ndumu Reserve. No releases have been specifcally aimed at maintaining the floodplain ecosystem&nbsp;and the services it delivers to support the livelihoods of local communities. In 2013, the Department of Water and Sanitation&nbsp;commissioned an Ecological Reserve study of the Usuthu/Mhlatuze Water Management Area, which incorporates the Pongola&nbsp;Floodplain. This paper describes two-dimensional hydrodynamic modelling using RMA2 to inform this flow assessment. Four&nbsp;computational Pongola Floodplain models have been developed since 1979, including cell-based, one- and two-dimensional&nbsp;approaches. The RMA2 model is based on existing topographical, hydrological and hydraulic information, and was calibrated&nbsp;and verifed for the period 2008 to 2010 using water-level data from the local hydrometric monitoring network. Generally, good&nbsp;replications have been achieved in terms of peaks, rising and recession limbs, recession of ponded pan water-levels, and low-flow river stages. The RMA2 modelling represents an advancement of previous hydrodynamic studies of the floodplain and&nbsp;contributes to an improved understanding of its hydraulic behaviour. Model application was for the 15-year period 1990 to 2004,&nbsp;and simulations included naturalised, present management (2014), and 7 potential dam operational scenarios. The results were&nbsp;post-processed for analyses in the DRIFT DSS, described in the companion paper.</p> ER -