Quantifying future water environment using numerical simulations: a scenario-based approach for sustainable groundwater management plan in Medan, Indonesia

Abstract

River water was the backbone for socioeconomic development in Medan city of Indonesia. However, because of the rapid global changes, the status of most of the river systems is very critical from the environmental, aesthetic, and commercial usage points of view. Considering frequent flooding event combined with water quality deterioration, it is very hard to realize concept of sustainable water development in perspective. Accordingly, this chapter studies the case of Deli River in Medan and focuses on assessing the current status as well as predicting the future (2030) situation using different scenarios while considering key drivers of global changes (e.g., climate change and population growth) with their mitigation measures. All these aspects have been studied considering an existing master plan of the Deli River. Extent for both water quality deterioration and flood inundation was evaluated using Water Evaluation and Planning (WEAP) and Flo-2D/HEC-HMS model, respectively, using two scenarios: business as usual (BAU) and scenario with measures. Result shows that there will be significant increase of flood inundation despite increased flood diversion. The flood inundation is expected to increase in 2030, especially inundation of 3–4.5 m depth in the central and northern part of Medan, and in the south along the Deli River. For water quality component, it was observed that current status of water quality throughout the river is very poor when compared with local guideline for class 2 (biochemical oxygen demand (BOD) <5 mg/L; Escherichia coli <1000 CFU/100 mL). In addition, it is even worse in the case of downstream locations of the river because of the cumulative effects of waste disposal and excess of untreated waste coming from upstream. From the result of BAU scenario, effects of both climate change and population changes are prominent in water quality status. Furthermore, this situation is expected to deteriorate further in 2030 when compared to current situation, due to climate change and population changes. For example, our results suggest that BOD and E. coli will be further deteriorating by 54.2% and 12.4%, respectively, on average. The previous result suggests that current management policies and near future water resource management plan are not enough to check the pollution level within the desirable limit and reduce the frequency of extreme weather events. These call for a transdisciplinary research in more holistic way for doing it sustainably.