Making a case for sedimentation29 June 2012
According to the International Sediment Initiative (ISI), sedimentation issues are often ignored because the scale of the problem can seem too overwhelming. Recent research by ISI is working towards creating a holistic approach to the remediation and conservation of surface waters, with the management of dams and reservoirs playing a key part. Suzanne Pritchard takes a closer look at ISI’s recent interim case study report.
The time is ripe for policy makers to understand the implications of planning and management decisions for the environment. This statement, made by the International Sediment Initiative (ISI), headlines the organisation’s recent report on sedimentation in large river basins.
“Water managers today face many complex technical and environmental challenges in relation to sediment management,” ISI acknowledges. The changing nature of sediment issues due to increasing human populations; the construction of more dams and weirs; plus recognition of the importance of sediment in the transportation of river contaminants means that different approaches to sediment management are required in river systems.
“Water availability is commonly the key concern for policy makers,” ISI says, “with water quality and sediment control issues often receiving less attention in water management policies and programmes. Sediment issues are often ignored due to a lack of information or understanding on behalf of policy makers who drive the water management process, or because the scale of the problem seems too overwhelming to be tackled in a meaningful way by regional water managers.”
To help remedy the situation ISI issued its report called Sediment Issues and Sediment Management in Large River Basins (an interim case study synthesis report) in 2011. Drawing on international experience in sediment measurement and management, its aim was to provide river managers with:
• An overview of sediment issues.
• Methods for collection of sediment data.
• Management strategies to help overcome any issues in catchments under their control.
Case studies have been produced for the Nile, Mississippi (US), Rhine and Volga river basins. Plus the Chinese Yellow, Haihe and Liaohe river basins, with the purpose of:
• Increasing awareness of erosion and sedimentation issues.
• Increasing understanding of erosion and sediment transport processes under different conditions.
• Improving the sustainable management of soil and sediment resources, by providing examples of monitoring and data processing techniques, technical procedures, and methodologies for the analysis of environmental, social and economic impacts.
• Assisting in the provision of better advice for policy development and implementation and evaluation of management practices.
Key issues relating to sediment management have been explored through the above case studies and ultimately recommendations for developing management strategies have been extracted from these experiences.
ISI believes that the case studies in its interim report provide a useful first step towards the global sharing of knowledge and experiences essential for best practice sediment control and management. ‘The hope is,’ the report states, ‘that these case studies will encourage further information exchange and sharing of data, and promote international dialogue on sediment control issues.
The case studies
Haihe and Liaohe rivers in China
Both the Haihe and Liaohe river basins are located in northern China. The Haihe river basin has an area of 263,400km2. The management plan for this river basin underwent expert review in June 2010 with the intention of making improvements and transforming this area into a third growth spot after the Yangtze and Pearl river deltas.
The report cites dam construction as the reason for trapping sediment and decreasing discharge. The basin has a mean annual sediment load of 0.15B tonnes in the lower area and a mean annual yield/basin area (km2) of 569.4 tonnes.
Incorporating two river systems, the Liaohe river basin has a total area of 220,000km2 which covers 15 cities, 56 counties and a population of approximately 35M. This highly urbanised area has been facing challenges to meet growing water supply demands and water authorities have been calling for ecological restoration.
Since construction of dams on the river the average annual run off has decreased from 5.67Bm3 (pre dams) to 2.89Bm3 (post dams). In addition the mean annual sediment load in the lower basin has fallen by 27.76M tonnes after dam construction. Again dam construction is blamed for trapping sediment apart from in the flood season when it is released from the reservoir.
Yellow river basin in China
The Yellow river is the second longest river in China at a length of 5464km. Often referred to as the cradle of Chinese civilisation, the river basin covers an area of 742,443km2. It accounts for 7% the country’s total area and has a decreasing sediment discharge. Land is still accumulating at the river mouth and a low flow to the ocean has been caused by large reservoirs trapping sediment. Estimates suggest that from 1919-60 the mean annual sediment load in the lower basin was 1.63B tonnes. From 1952-2000 this had declined to 0.8392B tonnes.
Mississippi river basin in the US
Draining the plains between the Appalachian and Rocky Mountains, the US’ Mississippi river basin is the third largest drainage basin in the world. It is the source of many river systems including the county’s two longest (the Mississippi and Missouri rivers).
The basin is home to more than 3000 reservoirs which are mainly used for flood storage and water supply, plus there are over 2580km of levees. It has a mean annual sediment yield/basin area (km2) of 64.01 tonnes. Recent measurements suggest that the annual suspended sediment load in the basin has declined by 50% since the main period of reservoir construction.
The Nile river basin
The Nile river basin covers an area of 3.1M km2 equivalent to 10% of Africa (incorporating Egypt, Burundi, Democratic Republic of Congo, Eritrea, Ethiopia, Kenya, Rwanda, Sudan, Tanzania and Uganda).
The area includes sections of the worlds’ five poorest countries but the dams in the basin contribute significantly to socio-economic development, providing hydropower, flood control and irrigation water storage. Effective water management in this region is considered a problem due to a lack of skilled manpower, poor management of water resources, traditional irrigation methods, and a lack of effective monitoring and evaluation. The Nile river basin is expected to be water scarce by 2025.
Egypt’s Aswan dam is found to be guilty of trapping sediment upstream with a mean annual sediment load at the dam estimated at 160M tonnes. The vast quantities of trapped sediment result in problems downstream of the dam. These include:
• An increased use of chemical fertilisers to replace nutrients once carried in sediment deposited during floods.
• Erosion of farmland on the river banks.
• Erosion of the coastline and degradation of the Nile Delta (including the fertility of ecosystems in the region).
• A decline in Mediterranean fishing due to a reduction in nutrients from upstream.
• Seawater intrusion in the northern portion of the delta.
The Nile basin is facing significant challenges in terms of sediment management and control. However, ISI says, management of sediment in Egypt is complicated by the presence of the Aswan High Dam which ‘traps virtually all the sediment that was previously transported downstream’. Possible solutions include artificial downstream supply of bedload via dredging and pumping, along with engineering solutions to allow passage of the finer sediment through the dam. In the longer term land management practices and afforestation should help reduce sediment loads.
Important progress to date has seen the establishment of the Nile Basin Initiative where nine of the ten Nile river countries have come together to focus on key actions to improve water management in the region.
Rhine river basin
Travelling through nine countries – Switzerland, Austria, Germany, France, Luxembourg, the Netherlands, Belgium, Italy and Lichtenstein – the Rhine river basin covers an area of 185,000km2. Again reservoirs are trapping sediment here which is estimated at 7.3M tonnes for the mean annual sediment load (Germany accounts for 2.75M tonnes of this).
Volga river basin in Russia
Covering 10% of Russia’s total land area, this river basin’s reservoirs provide a reliable source of water and hydropower for the region. However, there are serious concerns about the safety of drinking water. Around 42M tonnes of toxic waste are generated in the basin each year and estimates suggest that only 3% of the Volga river’s water is safe for consumption.
Again sediment discharge is decreasing. Pre-dam construction the mean annual sediment load in the lower basin was 26M tonnes. It is now estimated at 8M tonnes.
Although the impact of sediment has been under research for many years now, with many management options proposed for dealing it, ISI says as yet there are few true success stories. However, one example it does mention is in the Yellow river basin located in China.
Since the mid 1950s the Yellow River Conservancy Commission has implemented widespread land management changes in the basin, particularly focusing on the Loess Plateau region. Changes, including major dam construction, afforestation, terracing, construction of check dams and conversion of crop land on slopes into grazing land, led to a project successful in reducing sediment loads transported by the Yellow River.
Consensus on a well-defined procedure for dealing with sediment problems remains elusive, ISI states, because applying an approach suitable to one area may not always be of benefit to another. A key component of sediment control and management is adapting methods to suit the conditions present in different geographical locations. Indeed, sediment still poses a great technical challenge to engineers around the world.
A one-size-fits-all approach would not be an appropriate solution for managing sediment in international river basins. With this in mind, ISI’s following interim report recommendations are intended as a guide for river basin managers:
• Recommendation 1: Sediment management (quantity and quality) should become a part of all river basin management plans.
• Recommendation 2: Encourage soil conservation initiatives, particularly on steep agricultural land. A reduction in erosion usually corresponds to a much smaller reduction in sedimentation.
• Recommendation 3: There is a need to work with international agencies such as ISI in developing a commonly accepted international protocol for measuring erosion, sediment transport and sedimentation in river systems. The reports studied in producing this synthesis report demonstrate that different river basins can employ very different monitoring and data collection techniques and procedures.
• Recommendation 4: It is important that efforts should be made to involve the community in sediment control and management. This will provide them with sufficient information on how they can improve river health and contribute to sediment management.
• Recommendation 5: Sediment management must be based on a sound understanding of the sediment dynamics of the river basin involved. There is a need to clearly define the sediment budget or balance of a river system and collate available data to identify knowledge gaps and further enhance understanding of sediment issues on a global scale.
• Recommendation 6: Sediment management plans should be periodically reviewed to ensure that they are in line with international best-practice.
• Recommendation 7: The potential downstream impacts of any river structure and sediment management strategy must be considered. The sedimentation of reservoirs built on sediment-laden rivers is a serious problem. It should be seriously considered in the planning and design of such reservoirs
• Recommendation 8: There is a need for investment in capacity building to ensure that water management personnel understand and engage with sediment issues effectively.
• Recommendation 9: Further investment in sediment research must be encouraged, particularly in developing countries. To justify the additional cost of a sediment control or storage recovery strategy, an evaluation of the economic impact of sedimentation on agricultural irrigation schemes and reservoirs is needed.
• Recommendation 10: There is a need to increase institutional cooperation and collaboration with international partners to share research and experiences.
• Recommendation 11: The ISI network should include representatives from all regions of the world (with perhaps one representative who is a key expert in sediment from each of the major sediment-laden river systems of the world).
• Recommendation 12: The precautionary principle should be applied in sediment management.
The good news, ISI believes, is that countries around the world have begun to take sedimentation issues seriously. Furthermore information on success stories is slowly becoming available. It has generally been considered too difficult to determine a future outlook for sediment issues on a global scale. However ISI is encouraging policy makers, scientists and river managers around the world to share information and enter into an ongoing dialogue on sediment issues.
Established in 2001, ISI is a global initiative to assess erosion and sediment transport to marine, lake or reservoir environments. It is aiming for a holistic approach for the remediation and conservation of surface waters, ensuring a close link to science with policy and management needs.
|ISI final report update|
In December 2011 ISI representatives met to consider preparation of the final synthesis report for the case studies. The next steps were discussed, along with the possibility of developing an ISI database to catalogue the important figures from each case study report.