Indices

Indices

This page displays calculated scores and indices for:

• Habitat modification (HMS)
• Habitat Quality (HQA)
• Riparian quality (RQI)
• Energy and dimensions
• Agricultural fine sediment (ASL, FSA and ASR)
• Hydromorphological indices (CSI, CVI only, the other indices require an upgrade to cRHS plus) and
• Hydromorphological quality (HIR) for CSI and CVI only

- To calculate  all  indices, press

Quality indices (HQA, the River Habitat Quality index and the Riparian Quality Index) are classified into 5 classes that are represented using a number between 1 and 5 and the following colour code (see also the table below and the appendices for more detail):

• 1: Very high in blue
• 2: High in Green
• 3: Moderate in yellow
• 4: Low in orange
• 5: Very low in red

Pressure and impact indices (HMS, the three agricultural fine sediment indices and the Hydromorphological Impact Ratios) are classified into 5 classes that are represented using a number between 1 and 5, a percentage or a description associated to the following colour code (see also the table below and the appendices for more detail):

• Very low in blue
• Low in Green
• Moderate in yellow
• High in orange
• Very high in red

To preserve the integrity of the data, all scores based on cRHS data are not directly editable.

The following scores and attributes (circled in red in the figure below) that can be derived by hand and that do not rely on RHS data can be modified by users:

• Total agricultural fine sediment inputs in tons per year
• Local agricultural fine sediment inputs in tons per year
• Expected values for the Channel Substrate , The Flow Regime , the Geomorphic Activity and the Channel Vegetation Indices. If you want to calculate the hydromorphological indices by hand, you can download a spreadsheet online (see Appendix 2: Hydromorphological indices).

Please note that, provided that the relevant information is included to calculate the indices, the HIR, the Agricultural Sediment Load and Agricultural Sediment Risk indices may be recalculated after changing any of the fields mentioned above.

Description of RHS indices

Details about the indices mentioned below can also be found in the appendices and on the RHS website: http://www.riverhabitatsurvey.org/manual/rhs-indices/

• The Habitat Modification Score (HMS) quantifies the extent, potential impact and persistence of engineering structures on river channels, banks and riparian zones (Walker 2005). It is categorised into five classes representing increasing levels of engineering impact, from semi-natural to severely modified (Appendix 1). The HMS is split into sub-scores describing different engineering structures: culverts; bridges; outfalls and deflectors; bank and bed reinforcement; bank and bed resectioning; berms and embankments; weirs, dams and sluices; fords; poaching.
• The Habitat Quality Assessment (HQA) scores the occurrence and diversity of natural habitat features, land uses and floodplain features, such as channel substrate types, riffles, pools, woodland and wetland (Raven et al. 1998). The score provides an overall site assessment of habitat diversity and conservation value. To be meaningful, HQA scores need to be interpreted within the context of sites of similar type.
• HQA scores are classified into five quality bands following a ‘context analysis’ where the site HQA score is assessed against the distribution of HQA scores for sites of similar types using Jeffers PCA scores (see Context analysis). The outputs from the context analysis are the 'Baseline HQA class' on a scale of 1 (top 20% of sites of similar type) to 5 (bottom 20% of sites of similar type) and 'HQA class position' (ie the exact position of the site HQA score within the distribution of HQA scores for sites of similar type) are derived following context analysis.  
• The River Habitat Quality (RHQ) index combines HQA and HMS classes into one index representing the overall quality and integrity of river habitats (Appendix 1) (Walker 2005; Walker et al 2002).
• The Channel Substrate Index (CSI), Flow Regime Index (FRI), Channel Vegetation Index (CVI) and Geomorphic Activity Index (GAI) are derived using RHS spot-check data on channel substrate, flow-types, channel vegetation structure, erosion and deposition features, riffles and pools (Naura et al. 2016), (Appendix 2). The indices represent natural hydromorphological dimensions in British rivers.  The four indices were mapped across the entire river network at 500m interval using geostatistical modelling techniques (Naura et al, 2016). Each index was mapped twice to represent current observable (including any impacts) and semi-natural conditions. The maps of observable and semi-natural condition form the basis for the calculation of impact ratios (HIR). The hydromorphological indices weights represent the completeness of the records on which the indices were calculated (full record = 10 for the first 4 indices and 20 for the last 2).

Map of CSI using geostatistical techniques at every 500m across the 1/50,000 river network on a gradient from bedrock/boulder (blue) to gravel-pebble (green) and silt-sand-clay (brown).

• Hydromorphological Impact Ratios (HIR) are indices describing departure from natural condition and impact for four hydromorphological indices (CSI, FRI, GAI and CVI), see Appendix 4.
• The composite Hydromorphological Impact Ratio (HIR) combines individual HIRs for four hydromorphological indices/dimensions (CSI, FRI, GAI and CVI) to assess departure from natural condition and impact. The composite HIR varies from 1 (no impact/semi-natural condition) to 5 (very high impact), see Appendix 4.
• The Riparian Quality Index (RQI) combines information on bankface and banktop vegetation structure, bank material and modification in an assessment of riparian vegetation complexity, naturalness and continuity (Appendix 3).

• The Channel Resectioning Index (CRI) quantifies the number of occurrences of bank and channel modification by reprofiling or dredging along a 500m stretch. Resectioning is the most common modification type and the most prevalent in the UK.

For information on the calculation of indices, please refer to the River Habitat Survey website resource section: http://www.riverhabitatsurvey.org/manual/rhs-indices/

Agricultural Fine sediment indices

Provided your site is located in Great Britain, the software will extract information on agricultural fine sediment delivery to your site in tonnes per year and derive a series of indices representing Agricultural Sediment Load (ASL), Fine Sediment Accumulation (FSA) and overall Agricultural Sediment Risk (ASR). These indices were derived as part of research for the UK government and published in 2016 (Naura et al 2016).

Total agricultural fine sediment delivery represent all fine sediments transported from upstream in the water column and local sediment delivery (on site) through run-off and tributary inputs. The data are derived using modelling but can be entered by hand by the user.

Local agricultural fine sediment delivery represent all fine sediments delivered through run-off and tributary inputs.

The Fine Sediment Accumulation index is derived directly from your RHS site spot-check data for channel substrate.  Sites will be categorised according to the number of spot-checks with silt, sand or clay as:

• Very low = 0 spot-checks with fine sediments
• Low = 1 spot-check with fine sediments
• Moderate =2,3 spot-checks with fine sediments
• High = 4 to 6 spot-checks with fine sediments
• Very high = 7 to 10 spot-checks with fine sediments

The ASR combines the FSA and ASL using a matrix