Heated activity in the subsurface

Drinking water is warming up

The energy transition is upon us: the Netherlands must become ‘gasless’. This will also have an impact on the water sector. Alternative means of supplying heat, such as heating networks, will be implemented. This will certainly be necessary in our cities, where not everyone can generate their own heat. Ground excavation for the removal of gas lines, the installation of heating networks and heavier electricity cables all heighten the chances of failures in the drinking water mains. A second potential problem is that the heating networks and electricity cables release heat into the subsurface, which also warms up the drinking water. We’ve known about this so-called ‘urban heat island’ effect for some time, but it also affects the shallow subsurface, where the pipes are located. In an urban environment, where there are numerous anthropogenic heat sources, the ground is warmer than it is in a rural area. This also influences the temperature of drinking water and therefore the water quality. True, the biggest impacts of climate change will be felt many years from now, but a water distribution network has a long life-span. The replacement of water mains offers the opportunity to improve the network by, among other things, starting to take the impact of climate change into account now.

Limiting water warming

The joint research for the water companies has already contributed significantly to our understanding of the warming up of drinking water. We know that the soil temperature around the distribution pipes – those positioned about 1 metre underground, with diameters of about 60-200 mm – have a strong influence on the drinking water temperature at the tap; in fact, this influence is greater than that of the temperature at the water’s source. We know how weather conditions (air temperature, direct sunshine, wind, etc.) affect soil temperature. This also applies to the ground cover (paving stones or vegetation), to the soil type and moisture, and to the kind of external above- and underground sources. In one TKI Water Technology project, KWR, Deltares, the drinking water companies and the power utilities will be determining in the time ahead the minimum distance required between the heating pipes and electricity cables, on the one hand, and the drinking water pipes, on the other, in order to limit the warming up of the drinking water by these heat sources. In the 2018 research for the dune water companies, KWR and the dune water companies in the Randstad conurbation are studying how we can limit the influence of the weather as a source of heat – for example, by installing pipes in the shade or under grass, rather than fully exposed to the sun under paving stones.

Determining climate stress

In spite of the energy transition, the degree to which we can contain the expected climate change is unfortunately limited. We must therefore prepare ourselves for it. In the Speech from the Throne it was announced that every municipality would be required to conduct a climate stress-test  in line with the annual programme of the Delta Programme Commissioner. The model that KWR has developed for temperatures in the urban shallow subsurface is therefore also of interest to municipalities. Soil warming, subsurface climate stress, also has special implications for the ecology, groundwater level, and consequently for the foundations of buildings. Together with Sweco, KWR will be researching how we can get as detailed an understanding as possible of subsurface climate stress. This offers opportunities to tackle not only the water-on-the-street problems caused by climate change, but also for example guarantees the provision of drinking water over the long term.

Gondwana helps reach a solution

In the joint research for the drinking water companies over the last few years, we have worked on the design of the target structure: a model for an optimal organisation of the subsurface water-main network, which the drinking water companies can work towards gradually. The replacement of old mains offers a good opportunity to improve the distribution network. An optimal network performs well with regard to supply continuity, water quality and pressure, and does so under all sorts of circumstances, current and future. The design of such a network is not self-evident: optimisation software to support the design is therefore desirable. This is why KWR has created the software platform which different drinking water companies are using to develop their target structures. The software takes account of different water demand scenarios, supply security scenarios and replacement strategies. By connecting the soil temperature model and all kinds of geo-information to Gondwana, we can, when designing a network, by smartly selecting the pipe location, strive to limit as much as possible the degree to which the drinking water is warmed up. We can also use Gondwana to determine the optimal design for heating networks. It would moreover be fine if the design of heating networks and drinking water networks could take account of both networks’ position. In this way, not only do the different themes come together, but so too do the different subsurface stakeholders.