Master of Science thesis “Bypass - Itajaí-Açu”

Master of Science thesis “Bypass - Itajaí-Açu”

Wijs, J.W.L.

Winterwerp, J.C. (mentor)
Wang, Z.B. (mentor)
Van Overeem, J. (mentor)
Perk, L.M. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2013-10-03

The city of Itajaí is located in the province of Santa Catharina in Brazil. The people of Itajaí have been coping with flood risk for the past decades. During normal conditions the Itajaí-Açu River is a rather calm river that is used for navigation and the harbour area. Recovering from the past two floods in 2008 and 2011 have cost more than over several hundreds of millions of dollars. Next to flood risk the Itajaí area is also prone to erosion problems during high discharges. Next to these extreme events sedimentation and salt intrusion occur as a daily issue. A proposed solution is implementing a bypass to divert water from the river straight to sea. This thesis describes the impact on the main processes when this implementation is done. Research During the research phase 4 aspects are investigated: Flood risk, erosion, sedimentation and salt intrusion. This is done with Delft3D to investigate the different processes and to be able to look at the effect that these processes have on each other in the current and future situation. For flood risk it was found that a bypass that connects just upstream of Itajaí to the Itajaí-Açu has a very strong effect. It can lower the water levels during extreme events significantly by diverting a large portion through the bypass. For erosion it was found that flow velocities decrease significantly as well. However the good results regarding erosion will have a negative effect on the sedimentation issues which will be discussed later on. Flow diversion is a straightforward solution for erosion as it lowers flow velocities in the current branch. This only has effect downstream of the bifurcation point. For sedimentation it is found that the bypass cripples the tidal flow as the tidal prism only slightly increases due to lowered resistance in the downstream section (bypass and current branch). The capacity of the downstream section is a much larger increase compared to the current branch only than the increase of the tidal prism. Hence the tidal flow diminishes in the downstream section. As tide is the main mobilizer of sediment severe accretion will occur. For salt intrusion the low flow velocities will allow deeper intrusion. Also a landward forcing by density difference between fresh and salt water will force salt water to flow upstream in the current branch. Conclusions The bypass is a good solution if it can be closed during day to day conditions to prevent sedimentation and increased salt intrusion. It only needs to be opened during extreme events. However the total result in that scenario is a strong improvement compared to the financial and human losses that occur once or twice a decade in the current situation.

Coastal
Bypass
Itajai
Brazil
flood risk
sedimentation
erosion
salt intrusion
salinization

http://resolver.tudelft.nl/uuid:4d328efe-2189-4b33-a901-589658df4227

Student theses

master thesis

(c) 2013 Wijs, J.W.L.