BS 15843:2010 pdf download – Water quality — Guidance standard on determining the degree of modification of river hydromorphology
4 Principle
4.1 A standard protocol is described for assessing the extent to which the hydromorphological features of river channels, banks, riparian zones and floodplains are modified. These features have been divided into two groups – a larger group of “core features” and a smaller group of “subsidiary features”. Core features are used to establish “departure from naturalness” as a result of human pressures on river hydromorphology. Subsidiary features also include some that contribute to habitat quality assessment. The former can be determined without reference to river type using data from field survey, remote sensing, maps or local knowledge, whereas the latter require an understanding of the features to be expected in different types of river. Both this European Standard and EN 1 461 4 focus attention on river features as surrogates for river processes. Those making assessments, therefore, do not need to be trained geomorphologists, although some geomorphological input may be useful in determining the contribution made by subsidiary, type-specific features.
4.2 The principal output from this standard is an assessment of the modification of hydromorphological features of an entire river reach. A definition of the term “river reach” and its relationship with survey units is given in EN 1 461 4. However, the principles in the standard may also be applied to much shorter stretches, such as those requiring restoration, or where near-natural conditions need to be protected.
4.3 To ensure consistency in approach, the main feature categories are the same as those in EN 1 461 4. However, some minor adjustments have been made to the details to help facilitate scoring.
5 Determining the hydromorphological modifications of rivers 5.1 Feature categories Assessments are made for all of the feature categories listed in EN 1 461 4, some of which have been sub-divided into core and subsidiary features (Table 1 ).
5.2 Procedure for scoring
5.2.1 Annex A sets out guidance on how to allocate scores for each feature category. Table A.1 contains two separate procedures for scoring − using score band A with quantitative data, or score band B with qualitative data. Score band A is a five-point scale (1 = lowest degree of modification, 5 = highest degree of modification). Score band B is a three-point scale (1 , 3, 5; following the same general approach as for score band A). Users should state which scores have been assigned based on quantitative data and which on qualitative descriptions, as this determines the degree of confidence in the assessment. This note should also be added to any maps produced that show the results of river hydromorphological assessment. An attribute should be left unscored where the user is not confident in allocating a score.
5.2.2 Where the majority of scores have been derived from five-band scales users may wish to retain the five bands. Where the majority have been derived from three-band scales users may wish to change the five-band scores to three-band scores as follows:
5.2.3 For those features where scoring 1 = 0 % to 5 % change (features 1 , 2a, 7, 8, 9, 1 0), an asterisk should be added (i.e. 1 *) where the recorded change is only 0 % to 1 %. This is to highlight river reaches with extremely low levels of modification. A 1 symbol should be added (i.e. 5 1 ) to indicate extreme levels of modification.
5.2.4 The importance of each of the features in Table 1 for geomorphological and ecological functioning will not be the same. However, at present there is insufficient scientific evidence to justify differential weighting of the scores allocated.
6 Interpreting and reporting hydromorphological modifications 6.1 Modification scores 6.1.1 Scores should be tabulated as shown in Table 2. This process provides a range of options for different purposes, but shows clearly how each of the three combined scores (options 2, 3 and 4 in Table 2) has been derived.