Morphodynamics of estuarine navigation channel

The port of Kandla, which is situated in the north west of India and is subject to a large tidal variation of about 5 metres, is preparing a major expansion plan. The capacity of the harbour will be increased in two ways. Firstly the construction of several berths and jetties will allow more ships to be handled on a yearly basis. Secondly deepening of the harbour and its approaches will allow ships with a larger draught to call upon the port. It is this deepening that causes concern. The Kandla Port Trust (KPT) and the Central Water and Power Research Station (CWPRS) have calculated the amounts of cubic metres that will have to be dredged in order to raise the permissible draught from 10.7 to 14 metres. Especially the maintenance dredging posts a problem. KPT and CWPRS have calculated that between 90 and 111 million m3 have to be dredged annually to maintain the required depths. This is an increase by a factor 20 from the present 5 million m3. The costs that accompany this huge increase of dredging exceeds the extra generated income by large. As no details are known about the calculation methods of both KPT and CWPRS and the expected dredging amounts seem unrealistically high, a goal of this study is to simulate the future situation and determine the dredging amounts that will arise. A second goal is to determine the effects of training walls on the sedimentation in the approach channel, where the largest increase in maintenance dredging is expected. A process-based software package, Delft3D, developed by WLI Delft Hydraulics will be used to simulate the reality. The set up and calibration of the model has led to mixed results. In Kandla Creek, where the port is situated, the flow velocities calculated by the model resemble the measured data quite good. In the area around the approach channel (Sogal Channel), the flow velocities are too low in comparison with reality. This has consequences for the morphodynamics in the region. The morphological development in Kandla Creek shows better results than the morphological activity in the shallower vicinity of the approach channel, where little to no morphological change has occurred. The simulation of the future situation has led to the calculation of a significantly lower increase in maintenance dredging than found by KPT and CWPRS. Even though assumptions have been made the increase amounted to a more realistic magnitude of a factor 3. The costs that accompany this increase are significantly smaller than the extra income generated by the expansion. Implementing training walls to divert or contract the flow in order to decrease sedimentation by means of natural flushing of Sogal Channel will not be necessary from an economical point of view. The simulation of a few training wall layouts however has been done to obtain insight in the morphological development of the approach channel. The first concept consists of a wall in line with the main flow direction. The idea is to guide the flow more into the main channel creating more natural flushing and stabilising the channel in its present position. The effect of this proposal however is negligible, as the main flow isn't deflected enough. The flow velocity in the bend of the channel is increased only marginally, especially in the creek outfall. The extra erosion in that area isn't beneficial as the depth is large enough already. In order for this concept to be more effective a larger portion of the flow (both ebb and flood) needs to be directed into the channel and therefore the training wall has to be less in line with the existing flow direction. The model has to be adjusted to create a different alignment of the wall. The other two concepts block a part of the flow and only allow water to flow through the channel. This is done by implementing training walls perpendicular to the flow direction. The first of these concepts consists of a staggered wall, which does not block the flow completely. Water is able to flow through the wall, albeit that the flow is severely hindered. The second layout blocks the flow completely and all of the water is directed through the channel. Both concepts have a favourable effect on the morphological development of the bend in the channel, which becomes subject to erosion. The problem however is shifted towards other parts of the approach channel, which become subject to sedimentation. The effect is roughly twice -as large in case of total blockage than in case of the staggered training wall. The impact of these proposals is very severe. The rate of morphological change is very high as the present hydrodynamic situation is gravely affected. It is not clear what the effect will be in the long run. The results of the simulations have to be interpreted cautiously. In the process of modelling assumptions have been made. A few of these assumptions had to be made due to a shortage of data, while others have been made in order to simplify the problem so that it could be dealt within the scope of this study. The quantitative results cannot serve as a basis on which conclusions are formulated. A qualitative analysis however is possible, which can be found in this report. The overall conclusion of this study is that the best way to enlarge and maintain the maximum permissible draught is to increase dredging. The extra costs of the increase in maintenance dredging weighs up to the extra-generated income. Furthermore the impact of the different training walls is too severe and the uncertainties that accompany this impact in the long run are too plentiful.Hydraulic EngineeringCivil Engineering and Geoscience