Optimised long-term decision-making
Mike is a 45-year-old harbour manager working at an agency responsible for the waterside infrastructure of an international overseas port. He is responsible for securing accessibility of the port to the sea and for monitoring the operational water depth maintenance for maritime vessels. This is important as if the harbour, or parts of it, are not accessible by larger ships, in the long-term the harbour could lose its strategic importance in relation to other overseas ports.
The challenge for Mike
As the port is located in the delta of a large river, this makes it particularly prone to impacts from the interaction of offshore tidal effects and inland hydrological conditions. Sediments that are pushed upstream by tidal pumping during high tides and sediments that originate from the upper reaches of the river pose a major threat for providing sufficient water depths for maritime vessels. Therefore, sediments have to be constantly removed from the bed of the port and the fairway through dredging. In case of high flows from inland rivers, a large portion of the sediments are transported naturally towards the sea. In case of low flows from rivers upstream, more sediments enter Mikes’ area of responsibility due to tidal effects occurring downstream.
There are many restrictions regarding the permitted time frame of dredging, dredging volumes, issues of natural conservation and required technical resources of the special ships (hopper dredgers), which means the task of dredging requires several months of planning in advance.
The agency Mike is working for has three options to handle the sediments:
- relocating the sediment from the harbour downstream to a stretch of river where the sediment will be transported naturally to sea by the river current.
- transporting the dredged sediments directly to the open sea, which permanently removes the sediments from the tidal river;
- handling the sediment ashore in case of significant pollution;
The first option is seen as most ideal, two involves much more time and costs and option three is the most expensive one and not practicable for large volumes. Option one isn’t available during the summer months due to reasons of natural conservation.
Therefore, due to the strong dependence of the sediment dredging processes on the inland river flow, Mike requires forecast information on different time scales in order to optimise the sediment management.
For short-term planning, Mike uses an 8-day forecast available via the river information service. However, for his long-term planning he has to solely rely on the climatology of the observed flows in the past occurring at the same time of the year. This climatological information does not include highly relevant information on extreme flow conditions, which can lead to serious bottlenecks in the decision-making and planning. For example, Mike has seen situations in the past where most of the sediments relocated downstream were promptly transported back to the harbour by the tide, due to extreme low flows in the inland river. If Mike had known some months in advance that an extreme low flow situation in the inland river was possible, he would have chosen another sediment management option. Likewise, information about occurrences of higher flow is of great importance as in this case most of the sediments are transported to the sea through natural means and do not have to be removed with (expensive) technical measures.
Solving the challenge with IMPREX
Within IMPREX, monthly to seasonal pre-operational forecast products required for optimal long-term decision-making in this sector are developed, including in-depth knowledge about the skill of the forecasts. Using IMPREX results, a skilful monthly forecast is developed to support long-term planning of sediment management of the harbour. An in-depth analysis of IMPREX’s retrospective forecasts showed that the skill of these IMPREX products is better than that achieved with climatological information, which Mike had been previously relying upon.
Applying these new IMPREX forecasts operationally would assist Mike to make better decisions in the long-term, help his agency save money and reduce the dredging process’s impact on nature.