Sand Closure Bintan Bay

Sand Closure Bintan Bay

Huis in 't Veld, M.L.H.

Stive, M.J.F. (mentor)
Verhagen, H.J. (mentor)
Labeur, R.J. (mentor)
Van der Schrieck, G.L.M. (mentor)
Jansen, M.P.H. (mentor)
Kroon, J. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2015-02-26

In the region of the Riau Islands of Indonesia fresh water scarcity is one of the challenges the local community is facing. In order to increase the catchment of fresh water the choice is made to turn Bintan Bay, part of the Riau Islands, into a fresh water reservoir. Hereby collecting the fresh water runoff from local rivers. It is however unknown where the reservoir, and thus dam, will be positioned and whether the closure can be constructed with sand. This thesis focusses on those two topics. Based on an investigation into the hydraulic boundary conditions six alternative dam locations are defined. To weigh the alternatives a preliminary cost-benefit analysis is carried out. The outcome of the analysis is that the alternative in which the whole bay is turned into a reservoir can be considered most favourable. However, underlying assumptions and simplifications need to be verified in order to assess the effects on the outcome of the analysis. One of these assumptions is that a sand closure is constructible for all alternatives. This implies that additional effort, in terms of the required capacity of the dredgers, and sand losses are not included. To investigate these assumptions a more detailed research is carried out into the sand closure. The principle of a sand closure is fairly straightforward: the supply of sand has to be larger than the losses due to erosion in the closure gap to be able to close the dam. Since the sand losses are directly linked to the flow velocities in the closure gap a one-dimensional flow model has been created. This shows that maximum flow velocities at Bintan are higher than the limit according to a rule of thumb provided in literature. Therefore, the closure seems difficult, if not impossible. However, since a spring-neap cycle is applied a worst case scenario is simulated where also the critical closure stage is during springtide. This can be considered an overestimation of reality since it is common practise to close during neap tide. By introducing a sediment transport function and a sand input, the closure gap area is made time dependent. With this upgraded model, more realistic scenarios can be simulated where the critical closure phase is executed around neaptide. After optimizing, the maximal flow velocities showed a significant reduction while the production rate is high compared to other closures, but not unrealistic. The one-dimensional closure model has limitations in describing the flow velocities and erosion. Therefore, an additional two-dimensional model is set up in FINEL. The applied erosion function was already calibrated on the recent closures at the Maasvlakte 2, and is therefore regarded to provide more accurate results. Various simulations are conducted to recognise sensitivities and to identify the differences between the one- and two-dimensional models. The comparison shows that the original erosion function applied in the one-dimensional model indeed highly overestimates the sand losses. Because of this, new simulations are performed in the one-dimensional model with calibrations based on the MV2 closures. A comparison shows that for the identical dredger capacities the sand losses are significantly reduced. Therefore, a successful closure proves to be achievable with half of the original production capacity. Since all computations are conducted for the most favourable alternative, a final comparison is conducted with the other alternatives. This results in the conclusion that solely the sand losses will not result in another alternative to become more favourable in the cost-benefit analysis. However, dredgers that can achieve the required production capacity should be available in the area. If not, other alternatives might be cheaper to execute since these can be closed with smaller dredger capacities and thus smaller vessels.

sandclosure
sand closure
modelling
closure dam
alternative study

http://resolver.tudelft.nl/uuid:b94a0412-3f10-47d1-88ec-b1ae6002674a

Student theses

master thesis

(c) 2015 Huis in 't Veld, M.L.H.