Project members: Thomas Putranto, Thomas R. Rüde

Urban areas in Indonesia are characterized by rapid urban population growth and located in the coastal cities. The demand for clean water primarily from groundwater for domestic and commercial purposes increases continually in line with population growth. In Semarang, which is located in the north of Java Island, the number of registered deep wells increased tremendously up to 1,127 wells with an official abstraction of around 35 million cubic meters per year. The study area covers urban (Semarang city) and suburban (Demak, Grobogan, and Semarang Regencies) areas with a population of about 3 million inhabitants. Groundwater exploitation via deep wells concentrates on a confined aquifer system. This study aims at simulating groundwater flow in Semarang to the actual conditions as well as future change based on the city development and predictions of climate change using a numerical modelling.

This study is focused on major improvements to the existing hydrogeological model and applied it to simulate groundwater flow under steady state and transient conditions by integrating geological, hydrogeological and hydrological data. The numerical model is generated by applying the conceptual model. The numerical model is evaluated by quantitative and qualitative methods during the calibration and validation processes. The sensitivity analyses quantify the influence of the most sensitive parameters in the numerical model. Using the calibrated transient model, the model applications simulate the groundwater flow model under different prognoses based on future city development and climate change.

As result, the steady state model simulates hydraulic heads for the year 2010. For a successful calibration of the numerical model, groundwater abstraction has to be assumed at a much higher value compared to the official numbers (around 60 compared to 35 MCM/yr) while a higher draw down of the groundwater table in the northern part occurs compared to the surrounding areas as a result of intensive groundwater abstraction. Moreover, the consequences of climate change will lead to a high potential loss of groundwater resources in the future. The best solution is achieved by decreasing abstraction rates to recharge groundwater storage and to minimize potential losses of groundwater resources in the future. This should be a critical point for the decision makers at the local government (Semarang municipality) in order to manage groundwater use in the future