by Dennis Kuijk
June 9, 2020
In my previous blog I wrote about a technically feasible project in which getting the residents involved once again created added value. The residents were actually all on the same wavelength, and that helped make the project very successful. But what happens if one person’s solution is another person’s problem? If for example you want to retain water to meet your needs in dry periods, but the retained water causes moisture problems? You will need to find a course between sufficient drought containment and the lowest possible, acceptable moisture levels. And preferably not reach a compromise that everyone has a problem with, but one that is actually effective. What we now realise is that our own climate resilience is not that great. Our choices are subject to the whims of the seasons. In the summer the drought is palpable and we want to infiltrate and retain more water. A drought period apparently helps bolster water awareness. When the days again grow longer and rainy weather raises groundwater levels, we immediately react by calling for the discharge of as much water as possible.
Urban areas in low-lying delta regions actually confront numerous different challenges caused by the changing climate. The problems of water on the street or of heat islands are generally acknowledged. But this next example illustrates the conflicting interests I described above. For instance, I see high groundwater levels and poor soil permeability leading to the growth of moulds in buildings. But, of course, drought is again the ‘silent killer’ for both agricultural, and particularly urban areas. Urban green spaces dry up, wooden pile foundations deteriorate, land subsidence accelerates, just to mention a few examples – all problems incidentally that are in fact technically quite easy to solve on their own. But the quest for a joint solution is still not that easy if two problems arise simultaneously. Active groundwater level management is a good way of managing these kinds of problems in conjunction. The key to success lies in that little word: ‘active’. It means that you can adjust the dial to minimise the negative impact of groundwater level fluctuations for all those affected.
Active Groundwater Level Management
In the old city centre of Delft many of the houses have steel foundations, that is, they are built on a steel base on the ground, without foundation piles. This causes problems when the ground settles or sinks because of peat oxidation (land subsidence). Land subsidence leads to a diminishing drainage depth under buildings and roadways. In such cases, if you lower groundwater levels further this will lead to further subsidence, and so on. In many cases a sound system design using the Active Groundwater Level Manager (in its Dutch acronym, AGAPE) is enough to prevent both groundwater flooding and low groundwater levels. Even if every groundwater level has its harmful implications, in many instances an acceptable middle course can be found. This sometimes implies that a stakeholder has to accept some damage or inconvenience, or needs to invest in some construction work. Actually, I would dare say that an approach using the AGAPE, on the basis of a transparent and thorough appraisal of the long- and short-term consequences for all the stakeholders, can produce solutions acceptable to everyone. This requires a high commitment by citizens and public authorities in a preliminary phase. And it requires that we, as engineers, do our very best in presenting and explaining all the potential factors of influence as simply and as clearly as possible. By taking an integrated approach, combined with knowledge at different scale levels, we can effectively resolve problems. Municipalities can make a big difference in this context. Providing insight into the urban groundwater, outlining the groundwater requirements and conditions, and proposing possible solutions to property owners. To my mind, the municipalities have an important task when it comes to keeping deltas liveable and habitable!