Page 261 - Freshwater-Biology-and-Ecology-Handbook

3.2.5 HEV (Hydroecological Validation)

Hydroecological validation (HEV) is based on a graphical Specifically, HEV is used for:
comparison of ecological and hydrological data to help • reviewing and assessing EA Area drought plan
assess the ecological response at a site to river flow. A range monitoring data
of biotic indices expressed as Ecological Quality Indices • water resources investigations for river basin planning
are plotted with flow so that patterns in measured flow and (normal and heavily modified water bodies) and the legacy
the condition of the ecological community can be seen. Restoring Sustainable Abstraction (RSA) programme
(Note that EQIs are the observed value divided by the value • reviewing the Environmental Flow Indicator using the now
predicted by RIVPACS for un-impacted conditions.) HEV is defunct Catchment Abstraction Management Strategies
also used to infer the effect of other pressures, such as water (CAMS) invertebrate monitoring network
quality and fine sediment. • national drought monitoring and reporting
• water resource licensing (where existing data are
available).
HEV – Hydroecological
Validation HEV uses the following invertebrate biotic indices:
• Lotic Index for Flow Evaluation (LIFE)
Hydroecological Validation is based on a graphical • Proportion of Sediment-sensitive Invertebrates (PSI)
comparison of ecological and hydrological data to help • BMWP average score per taxon (BMWP-ASPT)
assess the ecological response at a site to river flow. • Number of BMWP-scoring taxa (BMWP-NTAXA)

The Environment Agency uses HEV to provide evidence of An EQI (O:E ratio) LIFE 10-percentile of less than the
where water resources activities, such as abstraction, might guideline threshold of 0.94 (from a data set with at least
be contributing to an ecological problem. In turn, this helps 9 samples) is used as an indicator of possible flow stress.
indicate where further investigation and possible action is In chalk streams and naturally sandy rivers, a guideline
needed to protect river ecology to ensure that water bodies threshold of 1.0 is commonly used because RIVPACS is
meet their environmental quality objectives. known to under-predict the expected condition in these
rivers. The Good/Moderate boundaries are used as guide
values for BMWP indices. These thresholds are used only
as a guide that must be supported by other evidence.

A refined version of HEV is in development.

Figure 5.14 Figure 5.15
Front cover of the Environment Agency’s Example of an HEV plot; horizontal lines are guidance thresholds
Operational Instruction for HEV

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