Related Rule
Netherlands
Practice Relating to Rule 42. Works and Installations Containing Dangerous Forces
The Military Manual (1993) of the Netherlands restates the content of Article 56 of the 1977 Additional Protocol I and specifies:
The normal function of a dyke is to hold back water or to be prepared for that function. When a dyke is used only to this effect it cannot lose its function, even if it carries a road and has a traffic function and even if that road is occasionally used for military traffic. Protection only ceases if the last two conditions are also fulfilled: significant support for military operations and no other means to terminate such support [than attack]. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. V-9/V-10, § 8.
The manual further states that “attacking … dams, dykes and nuclear power plants” in violation of IHL constitutes a grave breach. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. IX-5.
With respect to non-international armed conflicts in particular, the manual restates the content of Article 15 of the 1977 Additional Protocol II. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. XI-7, § 6.
The Military Handbook (1995) of the Netherlands states: “In principle, dams, dykes and nuclear power plants (works and installations containing dangerous forces) must not be made the object of attack.” 
Netherlands, Handboek Militair, Ministerie van Defensie, 1995, p. 7-44.
The Military Manual (2005) of the Netherlands states:
Section 6 - Dams, dikes and nuclear power plants
0537. Premise
The premise is that dams, dikes and electric power stations cannot be the target of attack. Even if such objects are, in themselves, military objectives, they cannot be attacked if this would cause a release of dangerous forces and thus heavy loss of life among the civilian population. Such a prohibition applies to attacks on other military objectives which are located on or near dams, dikes and power stations.
0538. In certain circumstances, the protection of these objects from attack is ended. For dams, weirs and dikes, this occurs if they are used:
- other than for their normal purpose; and
- in regular, considerable and direct support of military operations; and
- if the attacks are the only way of ending this support.
Power stations lose their protection if:
- they supply electricity in regular, considerable and direct support of military operations; and
- if the attacks are the only way of ending that support.
A dike’s usual purpose is to hold back water or be ready to do so. If a dike serves exclusively for this purpose, it cannot lose its protection; nor can this happen even if the dike carries a road and thereby also fulfils a transport function, even when that road is used incidentally by military traffic. The protection ceases only if the latter two conditions are met: considerable importance in support of military operations; and no other way of ending that support.
An example which can be quoted from the Second World War is the Allied attack on Walcheren in 1944. The Allied forces experienced major logistical problems while fighting their way through France, Belgium and the Netherlands in the autumn 1944 offensive. The difficulties could be solved only by using the port facilities of Antwerp. To do this, it was necessary to control not only southern Flanders, but also the area to the north of the West Scheldt. This included the Walcheren peninsula, where the Germans had erected powerful defences. These installations were designed specifically to deny access to the West Scheldt. From 3 to 17 October 1944, air attacks were directed at the dikes at Westkappelle, Veere and Flushing and as a result, large tracts of Walcheren were flooded. From late November 1944, the Allies were able to use the port of Antwerp. Viewed together, in present-day legal terms, the air onslaught was not an unlawful attack on the Walcheren dike system because it sought to gain access to the West Scheldt on behalf of the Allied operations in north-western Europe. 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, §§ 0537–0538 and 0540.
Under the International Crimes Act (2003) of the Netherlands, it is a crime, during an international armed conflict, to commit
the following acts, when they are committed intentionally and in violation of the relevant provisions of Additional Protocol (I) and cause death or serious injury to body or health: … launching an attack against works or installations containing dangerous forces, in the knowledge that such an attack will cause excessive loss of life, injury to civilians or damage to civilian objects. 
Netherlands, International Crimes Act, 2003, Article 5(2)(c)(iii).
The Military Manual (1993) of the Netherlands restates the content of Article 56(5) of the 1977 Additional Protocol I. 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. V-10, § 8.
The Military Manual (2005) of the Netherlands states:
The parties to a conflict must try to avoid locating military objectives near dams, weirs, dikes and power stations. Defensive installations built near such objects are permitted if their sole purpose is to defend the objects, and the armaments are limited to weapons suitable only for the defence of such objects. 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, § 0539.
The Report on the Practice of the Netherlands notes that no internal legislation has been adopted to implement the required separation between military structures and protected works and installations. 
Report on the Practice of the Netherlands, 1997, Chapter 1.9.