In the project Heritage uncovered; Tow barge canals in a water management context, the future value of tow barge canals for climate adaptation has been studied. The project focused on the area between the cities Leiden, The Hague, Delft, Rotterdam and Gouda, with a surface area of km2, and the tow barge canals the Vliet, the Schie, the Gouwe and the Old Rhine. Until 900 CE the areas was mostly peat swamp. Since then, it has been drained for agriculture. This has resulted in economic growth and the development of cities in the 13th Century. A side effect of drainage was land subsidence. In addition, peat was mined to supply the cities with fuel. To limit waterlogging, large drainage canals were dug, such as the Vliet and the Schie. In the 17th Century, many of these were modified to function as tow barge canals connecting the major cities.
It is expected that the water management challenges in the area will increase as a result of climate change. According to the climate scenarios for 2100 of the Royal Meteorological Institute, both heavy rainstorms and periods without any rainfall will become more common. On top of this, there are plans to build many new houses.
To prevent an increase in flood and drought problems, more temporary water storage can be created, but no less than 34 mln m3 of additional storage would be needed. 7.5 mln m3 additional storage can be created in the different polders, primarily to cope with peak rainfall events, while east of the town of Zoetermeer a new lake with 26.5 mln m3 of temporary storage can be created to supply water in drought periods, called the Bent lake (Bentmeer). Assuming 2 m difference between the highest and the lowest water level, the Bent lake would need to have a surface area of 13.3 km2. It can offer excellent opportunities for recreation and nature.
To transport water in and out of the Bent lake, a connection to the Rotte river in the south and the Old Rhine (Oude Rijn) in the north has to be made. This would restore an old shipping route. For the connection to the Old Rhine three options have been explored and for one of these a spatial plan has been made. In this option the Bent lake is connected to the existing Benthuizer canal (Benthuizervaart) and the Benthuizer canal is connected via a new canal to the existing Hoogeveense canal (Hoogeveense vaart), (see figures 15 and 16). Along parts of the new canal futuristic “green” appartements will be built with a view either on the canal or over the surrounding polders. To limit height differences for boating, the new canal will be constructed above the level of the polder. The new apartment buildings along the canal will also be built at a higher level, which will make them less vulnerable to flooding (see figure 1).
In all options the old tow barge canals are essential for transporting water to and from the Bent lake and discharging excess water onto the main rivers and the North Sea. In addition, they are a good entry point for telling the history of the landscape and reflecting on possible futures. It is proposed to construct a tow path along the new canal and make a replica of an original tow barge. This barge will be called the “Climate Barge” (Klimaatschuit) and can be used as a floating exhibition space and a location for future discussions.
The proposals in this report have not yet been developed in detail and the future is still very uncertain. Yet, we cannot wait until there is certainty. If sooner or later large-scale temporary water storage in this part of the country will be needed, space for this has to be reserved quite soon. The costs will be high, but the costs of inaction will be high too. And it offers new opportunities.