Rainfall fed inundation in greenhouse dominated polders: Research of water system assessments

Rainfall fed inundation in greenhouse dominated polders: Research of water system assessments

Albers, B.C.

Van de Giesen, N.C. (mentor)

Civil Engineering and Geosciences

Watermanagement

Water Resources

2011-07-18

Since the end of the last century, polders in the Netherlands have suffered from inundation due to heavy rainfall. Inundation occurrences in 1998 have led to large economic losses, especially in polders with a fast rainfall runoff process due to the high percentage of land occupied by greenhouses. This thesis focuses on water system assessments, conducted in greenhouse dominated polders. The water system assessment is divided in a technical analysis (using a hydrodynamic model) and an analysis on the cooperation between the different parties involved in water management. The inundation of 1998 had a large impact in the area managed by the water board of Delfland. As a reaction to the inundation, policies were created containing storage capacity standards for the open water of polders. Based on these standards the project ABCDelfland (Afvoer- en Bergings Capaciteit Delfland, in English: Drainage and Storage Capacity Delfland) was started, in which water systems of main canals and polders were assessed. The polder assessment was aimed at reviewing if the new standards were met. In the assessment the water board focused on the water system under its own control. The focus of that study was not on how to solve the inundation problem, but on how the open water system could comply with the standards. The solutions which were identified to make the water system meet the standards were financially not feasible. It was found that a better representation of the water system was needed to develop new solutions. Cooperation between the parties involved in water management would be needed to make this happen. This study was conducted to improve the assessment methods of rainfall fed inundation in greenhouse dominated polders. It uses the Oranjepolder (located in the management area of the water board of Delfland) as a case study, since inundation has occurred several times in this polder and is well documented and parties are engaged in finding new innovative solutions for the problem. In this assessment a form of participatory modeling was applied. Input for a new hydrodynamic model was given by all parties involved in the management of water in the Oranjepolder. The water board of Delfland is responsible for the management of the open water, the sewer systems are managed by the municipality of Westland and horticulturists influence the runoff to open water by the storage of water in basins. By sharing information and experiences during workshops, this research has been made possible. Through the cooperation of these parties, the important elements of the water system and the key to future solutions are identified. A hydrodynamic model of the Oranjepolder with a high level of detail is achieved. All important hydrologic processes are included. The hydrology of greenhouses is included on an individual level, resulting in a runoff to open water which represents the actual situation. Secondly, the channel flow model contains all channels and water structures located in the polder. This makes it possible to review inundation at every channel. Thirdly, the sewer system of the village Maasdijk is included in the model. Water flowing out of manholes and the interaction between the sewer and open water system are made visible. Finally, the aspect of overland flow is included. By taking all these hydrologic processes into account, predictions with a high level of precision can be made. The high level of detail and the high precision of the model lead to better insight in the factors that influence inundation. Testing the model with real rainfall data resulted in the identification of multiple inundation locations, which were also reported in reality. Due to this high predictive value it was possible to devise precise measures to prevent future inundation. These measures are not confined to the open water system but also concern the sewer system and the hydrology of greenhouses. It is expected that the total cost and amount of land needed, will be substantially lower than in previous assessments and that all stakeholders will support the implementation of measures.

greenhouses
polders
inundation
hydrodynamic model
participatory modeling

http://resolver.tudelft.nl/uuid:d2ade54e-5a27-4f71-8141-2f0bffe0a8b2

2011-07-21

Student theses

master thesis

(c) 2011 Albers, B.C.