Fisheries Impact Assessment
Many developments, including water abstraction for hydropower generation, can affect fish populations. These include affects on fish passage (both upstream and downstream), changes in migration patterns, alterations in habitat quality and quantity, morphological changes to the river corridor and physical damage to individual fish.
A typical impact assessment for a hydropower installation would evaluate the sensitivity of the site in terms of species present, habitat quality and type, and the potential impact on migration patterns. Appropriate mitigation may take the form of improved fish passage and a minimum residual flow. Sites vary significantly in terms of sensitivity and it is not possible to apply a generic abstraction regime to all sites. For more sensitive sites, a fisheries assessment is essential to achieve the right balance and hence efficient use of the resource, while ensuring the maintenance and protection of the ecology of the rivers.
Other components of a fisheries study include:
- Spawning and juvenile habitat availability and quality
- Fish population surveys, including electro fishing
- Eel surveys using specialist eel traps
- Macro invertebrate studies
- Assessment of fish migration/fish passage issues
- Redd surveys
- PHABSIM studies
A key consideration within any impact assessment is the existing quality of habitat present at a site. A balanced set of recommendations can only be made on the back of such data. Such an assessment would quantity the extent of spawning and juvenile habitat that would be impacted by a proposed development and suggest mitigation as appropriate.
Electro-fishing surveys are carried out to quantify and determine the demographic structure of fish populations. This helps to identify the sensitivity of the river and the degree to which a proposed scheme might impact the fisheries ecology.
Assessment of Barriers to Migration
Alterations in flow regime can potentially make existing barriers to migration worse than under natural flow conditions. If existing barriers are present at a site, it is crucial to understand how changes in flow may alter the ability of fish to circumnavigate a barrier. Standalone assessments of barriers can also be made, including catchment wide assessments, in order to plan targeted improvements for increasing the ease with which fish are able to migrate upstream in a river.
Physical Habitat Improvement
A huge amount of work around the UK is currently being undertaken to improve the physical habitat of the aquatic environment, both freshwater and marine. This includes improvements to the habitat quality in rivers and lakes. We have had extensive involvement in projects aimed at improving the physical habitat in these environments. Our work has focussed on projects investigating and designing improvements to fish passage at existing barriers to migration in river catchments, including (in addition to formal fish pass design): barrier removal (partial and total), bypass channel creation and low-cost easements.
We have also designed physical habitat improvements that include the creation of new spawning areas, calculations of appropriate flow regimes in off-channel habitat features and the design of artificial man-made channels to replicate 'natural' habitat features.
A PHABSIM (Physical Habitat Stimulation) study is a useful tool for assessing the impact of abstraction and altered flow regimes on a derogated stretch of river. A full study is usually only considered for large schemes where there is a significant potential impact. A cut down PHABSIM (see reports) is cost effective and relevant for smaller schemes.
Redd surveys are conducted to establish the importance of an area for migratory salmonid spawning. This provides a specific level of detail of relevance to proposed hydropower developments on river containing salmonids. Redd surveys are conducted during the spawning season (typically November - February) and species identification can be made from observation of the redds.
River Dove Hydro Electric Scheme
PHABSIM Analysis and Report
Date: August 2008DOWNLOAD
Castleford Mill Hydro Power Proposal
River Aire -Fisheries Assessment
Date: October 2009DOWNLOAD