UNESCO-ISI: Expert meeting on global river sediment data

Many social challenges which are related to the Sustainable Development Goals (SDGs) are intrinsically linked to the sediment topic and therefore require a sound data basis and understanding of sediment erosion, transport and deposition. The compilation of a global suspended sediment database could provide valuable information to solves sediment related challenges in the context of i) climate change, ii) the global water and carbon cycles, iii)  human pressure on river systems (including eutrophication and pollution) and iv) freshwater ecosystem restoration.

To discuss the added value of a global suspended sediment database the International Centre for Water Resources and Global Change (ICWRGC, Germany), the German Federal Institute of Hydrology (BfG) and UNESCO ISI, supported by the International Research and Training Centre on Erosion and Sedimentation (IRTCES, China), organized an expert meeting on global sediment flux data, which took place online on 25^th of May and 10^th of June 2021. 24 people from 8 countries participated in the expert meeting, including scientists and members of governmental and non-governmental organizations (inter alia from several universities as well as FAO Land and Water Division, UNEP GEMS/Water, European Commission’s Joint Research Centre, UNESCO category 2 centres, GEO Aquawatch, International Commission on the Hydrology of the Rhine). The meeting aimed to bring together users (scientist, environmental managers, remote sensing community) and providers of global sediment data from various international organizations to discuss i) the current quality and availability of global sediment data, and ii) what would be required from the scientific and management perspective.

Therefore, the participants discussed the state of the art on global river sediment dataset during the first day of the meeting based on the following questions:

·         Which global databases with (suspended/bedload) sediment data are available?

·         In which countries are (suspended/bedload) sediment monitoring data (e.g. national monitoring programs) available?

·         Where are major white spots (data gaps) on the globe, where good quality sediment data are lacking?

·         How are in-situ observations connected to satellite Earth observations?

·         What are the spatial and temporal scales (resolution and extent) of available sediment data?

·         What are quality ensured sediment data?

The relevance and the demand for a global sediment database was discussed on the second day of the meeting. Therefore, the participants aimed to answer the following questions:

·         What are the scientific demands on a global database?

·         What are the demands on (global) sediment data from a sediment management perspective?

·         What are the benefits of a global sediment database?

·         Which information (meta data / parameters) should be included in a global sediment database?

·         How to deal with uncertainties when upscaling to load calculations?

The presentations from various participants indicated that substantial efforts have been made by various groups to compile global sediments loads. These groups were facing similar problems arising i) from the scatter global distributions of available data and ii) the variable quality of the data and the variable length of sediment load records. These issues are demanding for a joined initiative at the global scale. It was argued by the participants that a major obstacle to such an initiative is the harmonization of the available data. To reduce the complexity of the topic the workshop attendees decided to concentrate on suspended sediments only, however recognizing the importance of bed load and sand transport. Currently, the comparability of suspended sediment loads between various river systems is in many cases limited by variable measurement techniques, variable spatial integration of the cross-section of the river and variable sampling intervals that can lead to strongly different load estimates given the strong accentuation of suspended sediment transport during short-term floods. Issues related to the divergent load estimated require i) global standards on measuring and processing riverine sediment fluxes (and how best to share data with quality check / uncertainty indication), ii) metadata standards (including the definition of minimum metadata requirements) to evaluate data quality, and iii) data formatting standards, to ease data exchange and reduce barriers to provide and use suspended sediment data.

To successfully proceed towards a global suspended sediment database an official mandate for a long-term maintenance of the database is required. The participants collectively agreed that a joined initiative under the umbrella of an international organization is beneficial to improve the excess and value of a global suspended sediment dataset. It was suggested by the experts of the meeting that a strong involvement of professional international organizations (such as FAO, WMO, UNEP, or UNESCO-IHP) will increase the acceptance of many countries to support the initiative and provide suspended sediment data, which are the heart of this initiative. Such a global dataset has many use cases in the scientific context, supports management in the context of agricultural systems, rivers, freshwater environments, reservoirs, coastal regions and water resources in general. The workshop participants work now on a technical brief to summarize the workshop outcomes.

The organizers thank the experts, who participated the meeting for their great support and builds on the results of the expert meeting to evaluate further steps to successfully implement a global suspended sediment database.

Contacts:

Thomas Hoffmann (Federal Institute of Hydrology, Koblenz, Germany): thomas.hoffmann@bafg.de

Renee van Dongen (ICWRGC, Koblenz, Germany): vandongen@bafg.de

Stephan Dietrich (ICWRGC, Koblenz, Germany): dietrich@bafg.de

(by ICWRGC and BfG)