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Sluice Gate options

Delta Water Management

IntroductionSince both security and infrastructure are of public concern, they are the main destination of public funds. However, as they can conflict with other interests and concerns of the general public, policymakers have to be alert that many more criteria are taken into account. This example is based on a decision to make changes to the Delta water management. The disastrous flood in 1953 was the reason the Government of the Netherlands embarked on a huge scale sea-defence scheme to defend the country from future flooding. These are named the Delta works they form a chain of impressive pieces of infrastructure that together defend the country from the sea. The dam in the Haringvliet has sluices that, since 1970, were only opened to allow the out-flow of excess fresh river water. These Delta Works had many positive effects on the freshwater ground table, on the water supply of towns and villages and on the inland water transport between the ports of Rotterdam and Antwerp which was not hindered anymore by tidal fluctuations. However. it also caused negative effects, particularly on the environment, by hindering the in-out migration of fish and ruining the rich estuary brackish water eco-system. The absence of tides also meant that large quantities of polluted river silt was deposited in the Haringvliet. In the 1990’s the concept of water management changed. This resulted in 2000 in a report “MER Beheer Watervliet sluizen, over de grens van zout naar zoet.” This report, which unfortunately is only in Dutch, can be down loaded here on the left. The data of the table on page 16 of this report are used to model the decision structure and to check its conclusion. These data have been entered in an Excel workbook, into a decision structure and then linked to the sheets where weighing of the mentioned goals and objectives is possible.

Goals and objectivesThe two goals of the water mangement are "Recover" partial recovery of the estuary ecosystem and "Sustain" a sustainable use of the waters for human activities. The first goal "Recover" is divided into three objectives: 'Process' the reintroduction of tidal function in the estuary; 'Features' re-establishment of the hydromorph and salt dynamics and 'Kinds' the return of estuarial flora and fauna. The goal "Sustain" is divided sector wise into Agriculture, Water supply, Fishery, Tourism, Shipping, and Other. It shows the estimates of investment cost that could occur in the five sectors for each sluice gate scenario. At the results level of "Recover" the results per each objective are for 'Process': Tide in Estuarial mouth, Tidal wave in Haringvliet, Tidal wave in Bieschbosch and Tide Disturbance days/year; 'Features': Number of estuarial ecotypes behind (In) the gates, Number of estuarial ecotypes before (Out) the gates, Area of silt ecotypes inside, Area of inter tidal area In and Area of inter tidal area Out; and 'Kinds': Macro-fauna, Fish, Birds, Vegetation types and spread fresh/brackish/salt.

More informationAll the data are entered in an Excel workbook. This workbook contains three groups of sheets: One group with the data on the 5 different sluice management alternatives; a second group of sheets in which weighting is possible at all the four levels, first for Sustain and Recover and then at all other levels and a third group that shows the ranking of the five alternatives. The contents of the excel workbook sheets is shown in the PDF file here on the left. The last pages of the PDF file show examples on how the changing in weights has an effect on the priority ranking of the fields to be demined. To open this PDF file, click on the button at the left. A click on the "Movie ON" buton shows in a movie the Exel sheets and the effects of weighting. The Excel file also can be obtained. A click on the button opens a secured "PayPal" site where after having paid €10 for the file with Paypal or a credit card, it will be possible in a "Click2Pay" site to download the file.

In ConclusionThree different weightings result in a another ranking of gate management options. The Ajar option seems to be a good middle of the road choice when both "Recover" and "Sustainability" are equal in weight. When most weight is given to "Recover", the sluice option "Ajar" ranks first. However, when most weight is put on "Sustainability", the "Storm-gate” option comes first. In 2000, the government decided for the “Ajar” option. The effect of this decision had, as could be expected, a negative effect on sustainability of the five sectors particularly of agriculture and the supply of potable water, and especially for those enterprises with water intakes near the sluices. More studies were needed on the effects of the "Ajar" option on the environment and also on the costs in order to avoid the negative effects. Not all parties from the other sectors were convinced on the benefits of the "Ajar" option. In 2010, a newly elected government, placing more emphasis on economics than on environment, agreed initially to review the "Ajar" decision. However, under pressure from the environmental sector and from the binding international EU agreements to keep one of the main entry points open, for allowing migrating fish to move in and out the Rhine-Meuse river basins, the Government accepted in June 2011 the Ajar option.It is suggested that a process in which different groups of experts, including representatives from science and relevant sectors, together contribute in collaboration, giving appropriate attention to weighting the many aspects that are involved in such decision, that this might have more easily resulted in broader support. It shows that in such a case, with the help of an Excel workbook application, the data and findings could be easily modelled and the ranking of the options be set out in a clearer, more flexible and transparent way.

AlternativesThis report examines the effect of five sluice management options and shows five alternatives:

No change in management.The gates are open forthy percent of the time even during high tide wich creates a salt water tongue in the rivermouth.Ninety-five percent of the time open results in recovery of the brackish water culture and of tidal fluctuations.Open most of the time and only closed during storm tides.The gates are slightly opened.

1. Null 2. Brokengate3. Tamed Gate4. StormGates 5. Ajar

The decision structureThe figure shows the decision structure with its four levels. This is the 'Head' part of the choosing. The report presents, in many tables, estimates for each of the five sluice management options. Based on this information, it concludes that the "Ajar" option is the priority choice. The report gives no attention to the weights of the different goals and objectives that are used in this decision. That is the 'Guts' part of the choice

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