China embraces flood management modelling
Two major projects using computer modelling software to manage potential flooding in China have been undertaken by DHI Water & Environment of Denmark. Jacob Høst-Madsen, head of the river and flood management department at DHI, explains how controlling and river water levels will avoid flooding of the Yangtze and the Songhua river basins.
>Decision Support System controls Three Gorges Dam
The construction of the Three Gorges Dam on the Yangtze River in China is well on the way to completion. Twelve of the planned 32 hydropower units are now in operation, and all other structures have been completed, including the 67 spillway gates at three different levels, the ship locks and the sediment and debris gates.
An inflow forecasting system for the dam has now been developed by DHI in cooperation with the Yangtze River Commission. The main purpose of the system is to provide decision support for the operation of the dam, so that the power production can be maintained while ensuring sufficient storage to control river water levels downstream and avoid flooding.
DHI was selected to develop this inflow-forecasting system having developed many similar systems over nearly 25 years. The first inflow-forecasting system was established for the Maithon dam in India in the early 1980s. Since then, DHI has installed flow-forecasting systems in more than 20 countries worldwide.
The systems are applied by authorities and dam owners for flood forecasting and warning as well as for management of reservoirs and other structures. The software has continuously been developed to meet the demands of the various users and stand today as state-of-the-art in flow forecasting and warning.
The inflow forecasting system for the Three Gorges Dam is linked to a network of real-time rainfall and river stations, providing data every 15 minutes to a central database. It uses the MIKE 11 hydrological and hydrodynamic modelling system to calculate catchment runoff and river flow, and a data assimilation facility is applied to ensure that conditions are identical in the models and nature at the time of forecast. This ensures a high accuracy of the forecasting even when some of the real-time data are missing.
All the dam structures have been included in the model and can be operated as defined by the user or automatically, to meet given target water levels. This is done in a pre-defined sequence.
First, the specified target power is generated using the required number of power units, considering the water levels upstream and downstream of the dam, the turbine characteristics and more. Secondly, the ship locks and sediment and debris gates are simulated in accordance with the actual and planned use.
Finally, the spillway operation is performed as defined by the user or automatically, depending on the selected control mode. In automatic mode, the gates are operated to keep water levels within given limits.
This forecasting process is controlled by the real-time decision support system MIKE FLOOD WATCH, which runs automatically at regular intervals. It imports the required real-time data, performs the forecast calculations, and issues the forecasts and recommended gate operations.
The level of the reservoir will be raised by the end of 2006 and again in 2009, once the dam and all power units have been completed. This will provide a significant flood retention volume, which can be freed whenever the forecasting system predicts a major inflow event. In this way, the dam can be applied to avoid or at least reduce the floods, which for centuries have been a threat to the huge population along the Yangtze River.
Flood forecasting will save lives in Songhua
The Songhua River basin covers an area of 557,000km2 and serves a population of 53.5 million people. The river basin is frequently exposed to severe flooding with recent major events in 1991, 1994, 1998 and 2003. The flooding has a great impact on industry, infrastructure, the environment and, of course, the population. The major provincial capitals of Harbin and Jilin are often hit severely by the floods and the oilfields near Qiqihar are regularly threatened too.
DHI Water & Environment of Denmark together with Mott MacDonald (UK) and the Institute of Water Resources and Hydropower Research in China have been awarded a major contract by the Songliao Water Resources Commission (SWRC) to develop a state-of-the-art flood management system for the Songhua River Basin. The project is funded under a loan from the Asian Development Bank and is implemented during the period 2004-2007.
This technology transfer project ultimately aims to develop the necessary expertise and technology at SWRC to actively and effectively manage floods. A comprehensive Flood Management Decision Support System (FMDSS) is being developed and implemented in close partnership with the client.
The project includes a very comprehensive local and overseas training component where the local flood management engineering staff is trained in state-of-the-art modelling and decision-support technologies.
The FMDSS will provide easy access to all relevant flood information including historical and real-time data, modelling results, damage assessment information, scenario analysis, reservoir management and optimisation and information selected for dissemination of flood warnings. The FMDSS includes very powerful state-of-the-art GIS tools in order to manage the very comprehensive data quantities and still enable a very user-friendly environment.
The Songhua River Basin requires a very flexible and robust modelling system. The size of the catchment and diverse river, flood plain and reservoir characteristics call for an integrated one-dimensional and two-dimensional modelling system.
The need for high forecast accuracy requires the application of an advanced data assimilation tool. This tool will utilise the analysis of measured data and simulated modelling results in order to decrease forecast uncertainty.
Many structures and major reservoirs require computational engines that are robust, fast and suitable for real-time systems. To satisfy user-needs, the modelling system must be able to run automatically with provision of forecast results, for example, every 30 minutes every day of the year. Therefore, automatic and intelligent data quality-assurance facilities will be provided.
At the core of the FMDSS will be the MIKE 11 modelling system developed by DHI Water & Environment. MIKE 11 is a professional engineering software tool for the integrated simulation of hydrology, hydraulics, water quality and sediment transport in estuaries, rivers, irrigation systems and other inland waters.
MIKE 11 provides an integrated approach for the analysis, design, planning, and forecasting all aspect of flood dynamics. It is the most widely used tool for the modelling of dynamic processes in open and closed channels, rivers and flood plains with thousands of users worldwide. It is delivered with auto-calibration tools in order to assist the local flood management engineers in setting up the very comprehensive modelling for the entire basin.
The flooding problems in the Songhua River Basin are, in many locations, of a two dimensional nature. To provide a sound modelling basis in these areas, the MIKE FLOOD modelling system is applied. MIKE FLOOD is a dynamically linked one-dimensional and two-dimensional flood modelling package combining MIKE 11 with the fully two-dimensional modelling programme MIKE 21. These programmes facilitate one-dimensional and two-dimensional modelling in the Songhua River Basin in a very flexible way and fully integrated into the comprehensive FM DSS system.
Real-time flood forecasting will include forecasting of water levels at many locations, including the Jilin and Harbin cities. The forecasting system will also include the operation of major reservoirs in the catchment such as the Baishen, Fengman and Ni’erji reservoirs. One of the objectives will be to provide decision-support and optimisation-guidance to the reservoir management staff in order to minimise flooding problems and possibly increase power production.
As a real-time forecasting tool, the MIKE FLOOD WATCH system will be applied. This modelling system will control all required tasks to deliver fast, reliable, high accuracy forecasts. MIKE FLOOD WATCH is installed in more than 20 countries and is designed for automatic performance with tailor-made user interfaces depending on client needs.
The FMDSS will include scenario management facilities and modelling results will be interacting with damage assessment procedures and calculation facilities. The objective is to provide the decision makers with potential scenarios and consequences of future decisions they may consider.
Holistic flood management where a large number of influencing factors may be evaluated and measured against each other well before they are implemented will not only preserve property, but also has the potential to save lives.
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