Open verdedigingswerk, Inundatiekanaal Utrecht

English translation

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Description

Cluster 401. Inlet and check sluice.

NEW HOLLAND WATER LINE

Introduction

BRIDGE WITH INLET AND CHECK SLUICE AT LUNET IV as an example of a barrier constructed in the 1930s to control inundation and fort ditch water levels. The raising or removal / destruction of bridges has been a proven means of warding off intruders since ancient times. Not only did this hinder or delay passage or crossing over a watercourse, a dry or wet ditch or a terrain depression, but an attacker also had to provide the means to possibly overcome the barrier. Wooden bridges were relatively quick to destroy, if necessary by setting them on fire. Stone bridges required a larger and more time-consuming intervention, although a explosive charge could sometimes quickly achieve the desired effect. The same applied to concrete bridges, such as this one, which formed part of the path / road along the east side of the inundation canal. However, in the case of a bridge with a dual function as an inlet and/or check sluice, destruction was hardly an option and this structure therefore had to be defended. It stands to reason that this bridge could (among other things) be defended by means of a barricade. The defence system of the New Holland Water Line was primarily based on the controlled flooding of (large) terrain areas. Controlled inundation required an ingenious system of water works, such as sluices, weirs and canals, with which the necessary water level could be set and maintained quickly and within narrow limits. Many different types of sluices were used, depending on where they functioned in the system. Sometimes existing navigation, drainage or check sluices were used, but many new ones were also built or existing ones were (significantly) adapted. Inlet sluices were used or constructed to allow water to flow into areas to be inundated. This function could be realised via different types of sluices, provided the water level in the area to be inundated was lower than on the supply side. Check sluices were especially used to maintain a (once set) water level: after water inlet, a more or less permanent closure was made to prevent backflow. At relatively high water on the supply side (thus from the outer water), inlet took place, followed by closure - usually by means of double schotbalk, with a clay packing between them. In a considerable number of cases, such systems were also used to bring fort ditch water levels up to level and maintain them, or to separate ditch water from outer water. The ditch system and the supply canal of Lunets I through IV on the Houtense Vlakte could thus be maintained at level after feeding from the inundation canal, or from the Kromme Rijn. The work was constructed in the late 1930s as part of the adaptation of the New Holland Water Line during the construction of the current Waterlinieweg and thus formed part of a series of comparable and related structures between Fort De Bilt and the Four Lunets with civilian and military functions.

The bridge and barrier were adapted at a later time by widening and partial closure of the openings. The width of the bridge was presumably increased by the addition of a footpath with balustrade on the west side. Both openings were (presumably at the same time as the widening of the bridge) closed off on the west side with concrete plates, in which iron sluice gates were incorporated.

Description

BRIDGE WITH INLET AND CHECK SLUICE AT LUNET IV, executed in reinforced concrete and consisting of an approximately 10 m long plate structure, 6 m wide in total, between two approximately 4.50 m projecting, also concrete abutments of 9 m width. The originally possibly only approximately 4 m wide bridge deck is bounded on both sides by concrete parapets, provided with an iron railing. The inlet and barrier are executed in the form of two parallel openings separated by a semicircular-ended concrete pier projecting on both sides of the bridge. Outside the concrete plates as barrier, recesses are incorporated in the abutments for the possible lowering of beams.

Valuation

The BRIDGE WITH INLET AND CHECK SLUICE AT LUNET IV is of general importance because of:

* Cultural-historical values as part of the New Holland Water Line as designed by C.R.T. Kraijenhoff and initially constructed from 1815 by him, Jan Blanken and major-engineer Willem Offerhaus, and subsequently strengthened and improved by others over approximately 125 years.

* Architectural-historical values, in particular as an expression of military-strategic architecture, which is based on: a. the inundation and access defence system (19th century), b. the race with increasingly powerful offensive weapons (19th and 20th centuries), c. the system of 'living' field fortification in depth (20th century).

This concerns a component from the period 1935-1940, namely an expression of historical water engineering related to military-strategic architecture, serving as a military and civilian bank connection and water work.

* Ensemble value and situational values as part of the New Holland Water Line. Also because of the functional and physical coherence with the other components of the complex and with a number of related structures dating from the same period that were constructed due to traffic infrastructure developments.

* The component is representative (characteristic) because it is, in conjunction with nearby structures, a good example of the application of this type of bridge and barrier in a military situation.

* The component is reasonably well preserved because it has remained recognisable in form and situation, but through functional adaptations has nevertheless also lost part of its distinctive military character.