Old Delft Water Walk
We turn right after 150 meters to the Kolk and then the Geerweg. Here you are at the first weir in the Kantoorgracht canal. You also see a blue gauge with white numbers and the NAP (Dutch Ordnance Datum) level in red. The sensors in the two metal cylinders measure the water level before and after the weir. This information is used to automatically open or close the weir.
This weir is one of eight weirs that protect the eastern part of Delft’s city centre from flooding. This part of the city is very low-lying (see Land Subsidence). At some places, the quay is only about 10 cm above the canal water, such as along the Rietveld (stop 11) and Vlamingstraat (stop 12). Heavy rain showers caused significant flooding there. To minimize such annoyance, the “Afsluitbare Binnenstad” (Çlosable Inner City’ – the historic city can be closed off) was introduced. This concept consists of eight controlled flood barriers that can be closed depending on the weather forecast. If the water level in the closed-off city centre does become too high, the pump at the Duyvelsgat pumping station (stop 8; weir 2 in map below) is activated. Moreover, if more than 40 mm of rain is predicted within 24 hours, the water level in the Afsluitbare Binnenstad is lowered by 20 cm creating a buffer to accommodate for the heavy rainfall.
Six so-called valve weirs have been installed in the Kantoorgracht (weirs 1 & 2), the Voldersgracht (weir 5), the Oude Langedijk (weir 6), the Oosteinde (weir 7), and the Achterom (weir 8). A sliding gate has been installed at the end of the Rietveld (weir 3) and the Vlamingstraat (weir 4).
The eight weirs to close off part of the historic city at high water.
