Gera River Health Index — how it’s computed
Published · Data: EA WFD Cycle 3 (2022 (Cycle 3 assessment)) · OGL v3.0
Summary
The Gera River Health Index (GRHI) is a transparent 0–100 composite computed from real Environment Agency WFD Cycle 3 (2022) classification data. Per water body: GRHI = 0.6 × ecological_score + 0.4 × physico-chemical_score, where High=100, Good=75, Moderate=50, Poor=25, Bad=0. If physico-chemical data is unavailable for a water body, the GRHI is 100% ecological. Management catchment GRHI = simple mean of constituent water-body GRHIs. No number is estimated, adjusted or fabricated. Source: EA Catchment Data Explorer bulk CSV, OGL v3.0.
1. Source data
All classification data is downloaded from the Environment Agency’s Catchment Data Explorer (England/classifications.csv). The file contains 1,393,216 rows spanning all WFD classification items, water body types and assessment cycles.
The GRHI uses data from Cycle 3, 2022 — the current operational cycle. It covers 4,043 surface water bodies (rivers, lakes, canals, coastal and transitional waters) across England.
2. Classification items used
- Ecological status (Classification Item = “Ecological”) — the primary WFD status for surface water bodies, reflecting biological quality elements (fish, invertebrates, macrophytes, phytobenthos, phytoplankton) and hydrology. Weight: 60%.
- Physico-chemical quality elements (Classification Item = “Physico-chemical quality elements”) — covers dissolved oxygen, pH, temperature, ammonia, phosphate, BOD and salinity. Weight: 40%. Where unavailable for a water body, the GRHI defaults to 100% ecological.
3. Status-to-score mapping
| WFD Status | Score (0–100) | Meaning |
|---|---|---|
| High | 100 | Pristine / near-natural ecological state |
| Good | 75 | Minor human impact — WFD target threshold |
| Moderate | 50 | Moderate human impact |
| Poor | 25 | Significant human impact |
| Bad | 0 | Severely altered |
4. GRHI formula
Per water body:
GRHIwb = round(0.6 × eco_score + 0.4 × pc_score)
If pc_score is not available:
GRHIwb = eco_score
Per management catchment:
GRHIcatchment = mean(GRHIwb for all water bodies in catchment)
5. National context
- England average GRHI: 54/100
- Water bodies at Ecological Good or High: 14%
- Total assessed surface water bodies: 4,043
- Management catchments ranked: 105
- Assessment year: 2022 (Cycle 3 assessment)
6. Licence & attribution
Source classifications are published by the Environment Agency under the Open Government Licence v3.0. Gera computes only the GRHI composite; all underlying WFD classifications are reproduced verbatim.
Contains public sector information licensed under the Open Government Licence v3.0.