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De Rivier de Merwede, van ontrent de Steenen-hoek, Oostwaards-op tot verby het dorp van Sleeuwyk: me....

For a long time, the Merwede River formed one of the biggest problem areas in the Dutch river system. Especially after the Sint-Elisabethflood in 1421 - when the Biesbosch had the opportunity to develop gradually - the hydraulic situation became precarious. Along the undyked southern bank of the Merwede was the northern boundary of the extensive Biesbosch. This area consisted of many watercourses, so-called kills, which carried most of the Merwede water to the North Sea via the Hollands Diep. However, the Merwede itself had less and less water to swallow, which made it difficult to keep the river at the required depth.

For the harbour cities of Dordrecht, Rotterdam, Delft, Schiedam and Brielle, good navigability of the Merwede and, downstream, of the Lower Maas was of economic importance. These cities did everything in their power to guarantee shipping on both rivers by fully or partially closing off the Biesbosch. However, the problem was that the city of Gorinchem and the water boards upstream had great difficulty with a closure of the Biesbosch. After all, they benefited from a safe discharge of water and ice through an open Biesbosch. Closing off this drainage area without simultaneously reinforcing the northern river bank was unacceptable to them.

This 18th century contrast between the five Maassteden and Gorinchem forms the backdrop of this beautiful and detailed map of the Merwede between Woudrichem and Hardinxveld, made by Nicolaas Cruquius (1678-1754) in 1729-1730. At the time, there was ongoing discussion about the way in which the improvement of the Merwede's hydraulic status should be tackled. Between 1726 and 1746 the States of Holland made three frantic attempts to find a solution, each time accompanied by river engineering reports and accompanying maps. Cruquius' map was made for the second attempt in the period 1729-1734.

In February 1729, as in 1726, we were again confronted with high water levels and ice masses. A large ice dam had formed near Giessendam, closing the Merwede and thus blocking it. Because of a breach in the Waal dike, the Tielerwaard was under water and the water accumulated in front of the Lingedijk. For a moment, people feared a repetition of the events of 1726, when this dike broke. Fortunately, there was movement in the ice dam at Giessendam, which allowed large amounts of water and loose ice floes to be discharged through the channels of the Biesbosch. Several dams that had been erected here in 1727 and 1728 fell prey to the water and ice currents. However, the water level in the Merwede rapidly dropped and with that the danger of dike breaches and floods had temporarily disappeared.

The city of Gorinchem thought that the events of 1729 showed that the Biesbosch channels should not be closed without also constructing a spillway through the Land van Altena. Because the States of Holland were not convinced, they decided to submit Gorinchem's proposal to three neutral experts, among them the surveyor Nicolaas Cruquius. They had to draw up an improvement plan in a short period of time, but it would take a year before this would be written down. The report showed, among other things, that the Merwede had a very irregular depth. In addition, there were large differences in flow velocity. It appeared that as much as two thirds of the Merwede's water mass drained via the Biesbosch.

Cruquius' map provided a fine visualisation of the above-mentioned water problems. It shows that near Gorinchem, the water of the Maas, the Waal and - to a much lesser extent - the Linge gathered in a kind of basin. A little further downstream the riverbed narrowed, but here the water and ice could still spread over the outer dike marshes and pilot whales. A little further on, at De Bout, however, this was no longer possible, causing ice dams to form frequently. A good flow was further impeded by the narrowing of the river between Werkendam and Hardinxveld, the harbours of the former, the floodplain vegetation and the local tidal effects. Because of these factors, there was a lot of sedimentation and the Merwede was in danger of becoming unnavigable, was the conclusion of the researchers.

The improvement plan was based, firstly, on removing obstacles in the river's winter bed, such as shortening the harbour groynes. Secondly, the plan provided for the construction of a spillway through the Land van Altena or via the north bank of the Merwede. On completion of this spillway, the Oude Wiel, the large channel to the Biesbosch, was to be dammed up, providing an opening for shipping towards the local villages.

Cruquius' river map was an integral part of the recovery plan. The map took a long time to make, over 400 working days, partly due to the high water levels. In addition to the two-page main map, Cruquius also produced an overview map based on existing map material. Here two rectangles show the area covered by the main map. The survey map also shows the entire Merwede basin, thus placing the water issue in a broader spatial context. Some cross-sectional profiles and tidal graphs complete this context image.

The main map of Cruquius, which is presented here, shows a detailed image of the river at that time and the most important adjoining areas in terms of river engineering. Much attention is paid to hydraulic facilities such as locks, dikes, bridges and wheels. Land use is also very specifically depicted, using no fewer than five different surface symbols. These symbols, mostly referring to grassland, reed land, osiers and orchards, are not explained on the map. For this, one must consult the accompanying final report.

However, in spite of the detailed nature of the main map, only the outer boundaries of the measures proposed in the recovery plan are indicated with dotted lines. These measures are better presented on the aforementioned general map. However, it can be seen that especially the spillway area in the Land of Altena has been mapped with a higher density. This is in contrast to the projected spillway area along the north bank, which was clearly less preferred by the experts. The question is, however, whether Cruquius thought the same way. After all, by accentuating the southern spillway so heavily and plot by plot, it became immediately clear whose lands would flood if the spillway were used. Cruquius probably wanted to demonstrate that a phased closure of the Oude Wiel was the best solution, preserving as much water as possible for the Merwede.

Another striking feature of the map is the system of depth lines in the river. The map is internationally renowned for this, as it was the first time in history that such a system of depth lines was used on a printed map. Maps had been provided with a single depth line before, but Cruquius was the first to use the so-called contour line method to connect a complex of depth lines. The starting point was a series of rays, perpendicular to the shore, along which the depth was determined by means of long poles (in feet below low water). Based on this data, the system of depth lines was then drawn by interpolation. Cruquius was not entirely faultless in this. On a contour map the lines cannot branch, but they do on his map. For instance northwest of Loevestein, right above the figure '38'.

The final report with the accompanying maps was presented to the States of Holland in July 1730. However, the disputes between Gorinchem and the five Maassteden meant that a difficult compromise was only reached in September 1730. This meant that no spillway was built and also that the Oude Wiel was not dammed up. What remained of the recovery plan was merely the clearing of the riverbed, which was done only to a limited extent.

Although the main map consists of two sheets to be assembled, it is possible to consider both sheets as separate maps: they have their own titles. The map sheets were engraved by David Koster. The printed map of Cruquius was an annex to the resolution of 12 July 1730 concerning the 'Report of the professors 's-Gravesande and Wittichius, and of the surveyor Cruquius, by virtue of their inspection of the river Merwede from Gorinchem downstream, and by virtue of the means employed to prevent inundation'.