Standards Development

Scope

This document provides guidance on the collation of the measurements required for the management of siltation at river structures. These include structures used by water supply utilities, other major water abstractors, HEP producers, and for flow measurement by environmental protection agencies.

The document is also intended for use when a redundant structure is being removed, or when modifications to a structure are being made to facilitate fish migration or for river restoration. This is to ensure that the impacts of these changes are adequately monitored and recorded.

The document covers the provision of routine measurements, and the checks and requirements that need to be made by the operator so that specific basic information is collated and made readily available. This information is used to inform decision-making by environment management agencies that authorise flushing, sediment clearance or sedimentation removal. This is to ensure minimal environmental impacts, and to compliance with existing environmental legislation.

Purpose

Worldwide, over half the water utilised by mankind is abstracted from rivers and streams. These are indispensable sources of water for public consumption, industry, agriculture and HEP. However, sedimentation, the product of land and river erosion, reduces the efficiency and effectiveness of man-made structures by which rivers and water abstractions are managed and controlled. Consideration also has to be given to fish passage and the impact of sedimentation on fish passes installed at control structures.

The removal of this sedimentation from around these structures is the usual way to rectify this loss of efficiency, but this causes numerous problems. These include:-

• The disruption of the natural channel-bed sediment feeding process. The optimum frequency of sediment removal must therefore be determined;

• The minimisation of impact on natural habitat around the structure;

• The minimisation of impact on water quality below the structure during sediment removal;

• The determination of the biological and chemical nature of sediment that has built up in, around or behind the structure.

The consequence of this situation is that when an operator such as a water utility or private individual, seeks permission from the local river protection or management agency to remove sediment, lengthy delays are sometimes experienced. These delays usually occur whilst adequate information is collected and all aspects of the agency’s requirements are met. This can result in a significant loss of operational value, system yield and data accuracy.

The proposal is to establish a specification that prescribes the requisite information and measurements of sedimentation that need to be available for operational river structures so that informed and timely decisions can be made regarding the need for and impact of the sediment. This will include recommendations for the routine compilation of such measurements and other information to inform the decision-making process. The specification will be expressed in generic terms with the facility for local interpretation.

This specification will help inform decision making by environmental protection, river management and other concerned agencies so that flushing of structures or clearance of intakes can be permitted in such a way as to minimise the environmental impacts. Similarly, the specification will be used by these agencies if redundant structures are being removed. This will help minimise the impact on the riverine environment.