River Condition Assessment
Survey Overview
A river condition assessment may be required for any projects situated within 10m of a watercourse to inform biodiversity net gain requirements. This excludes ditches and culverts which are fixed at ‘poor’ condition within the Statutory Biodiversity Metric.
Survey Methodology
A river condition assessment must be undertaken by a qualified surveyor and comprises two components – a field survey and a desk study.
A Modular River Physical or MoRPh survey is used to characterise one or more watercourse sections within the red line boundary of the development or project area, by sampling short subreaches, to capture the morphology, sediments and vegetation structure plus modifications of the river channel and margins within 10m of the bank tops within each watercourse section.
The desk study determines the type of watercourse using measurements of planform, natural confinement and valley gradient of the extended river reach enclosing the project area as well as information on the bed material of the river.
The results of both the field survey and the desk study are combined to generate a final condition class for each subreach, ranging from ‘poor’ to ‘good’. The condition will be moved down a condition class if the watercourse is considered to be over-deep. This data will then be inputted into the Statutory Biodiversity Metric to inform biodiversity net gain requirements.
Key Survey Considerations
MoRPh surveys can be undertaken at any time during low flow but are best completed in spring-early summer or late autumn, when both physical features and vegetation structure are clearly visible.
Further Information
The survey will be undertaken in accordance with the following publication:
- The MoRPh Survey Technical Reference Manual (2022).