BS/EN 17123-2018 pdf download.Water quality – Guidance on determining the degree of modification of the hydromorphological features of transitional and coastal waters.
A standard protocol is described for assessing the extent to which the hydromorphological features of TraC waters are modified by human activities; transitional waters include estuaries, lagoons, deltas, nas and fjords. These features have been divided into two groups — those that describe the static, structural features, i.e. shape, underlying geology, sediment patterns, etc., and the dynamic, functional processes, including water movements, sediment budgets and water characteristics. All of these are given as generic types but can be adjusted in a site-specific context and are used to determine any “departure from naturalness” as a result of human pressures on the hydromorphology of TraC waters. Those structural and functional attributes then provide the fundamental niches that are colonized by organisms and thus produce the biological assemblages characteristic of these areas.
The structural features often can be determined from easily available maps, charts, aerial photographs, databases, or by remote sensing. The functional processes, on the other hand, need to be determined within each water body and, given the high spatial and temporal variability in these features, usually require an intensive sampling campaign or modelling procedure and also detailed and specialized analysis and interpretation.
Given the difficulty in determining some functional attributes, both this European Standard and EN 16503 gives more attention to TraC structural features which can be regarded as surrogates for hydrodynamic processes. For example, the bed sediment grain size may reflect the hydrodynamic regime.
The main output from this standard is a method for the assessment of the modification of hydromorphological features of an entire estuary or other transitional water (TW), a part of it, or a length of a coast. This Includes parts of the TraC water bodies requiring restoration because of recent or historical modification, or where near-natural conditions need to be protected.
5 Determining the hydromorphological modifications of transitional and coastal waters
5.1 Survey strategy
The scale of survey is important in hydromorphological assessment of TraC waters, especially with respect to resolution and connectivity, and in assessing the severity of impacts. Different survey techniques are scale-dependent. Different applications require different levels of detail. In some instances, survey may be extended beyond the hydromorphological units of interest to provide a complete picture of the relevant physical processes involved. (For further details on survey strategy, see EN 16503:2014, 4.2.)
Timing and frequency of survey will vary among the different TraC waters because of their individual dynamic behaviour, and will depend upon the reason for assessment. Hydrodynamic attributes should generally be recorded at a higher frequency than morphological attributes. The timing of survey will depend upon the objectives of the work and the methods used.
5.2 Defining hydromorphological units
Units for assessing TraC waters should be defined using morphological features, geographical units and discontinulties in coastlines, water column characteristics, coastal cells, inputs of fresh water, and dimensions. Thc aim should be to delimit manageable areas for hydromorphological assessment.
Coastal waters may be dynamic and long-shore boundaries should be identified. These can be defined at various scales, depending on the purpose of the study. No one definition of the landward boundary of coastal waters accurately fits all conditions. Highest Astronomical Tide limit provides a consistent and definable landward boundary, although internationally recognized baselines are now used to delimit the start of territorial waters. In non-tidal or micro-tidal systems, a locally agreed high water mark. which allows for storm surges, will suffice.
The seaward boundary of coastal waters is usually defined geo-politically based on distance from the accepted baselines — normally to the 12-mile limit although this has no scientific justification. For the purpose of hydromorphological assessment, the seaward limit along active shorelines in coastal waters is the boundary beyond which significant nearshore hydrodynamic changes (e.g. sediment transport) cannot be detected. For rocky coasts, where such processes are less significant, a more pragmatic seaward limit can be set, such as the 1 nautical mile boundary in the WFD.
For hydromorphological assessments of transitional waters, a whole estuary approach” works well for small and medium-sized estuaries. In large estuaries, geological constraints combined with greater contrasts in wave energy dissipation can produce two or more distinctive “behavioural zones” within the estuary. Transitional waters (except for non-tidal lagoons) where not constrained by artificial structures, often do not have clear boundaries with surrounding habitats. However, their boundaries need to be defined in a consistent way so that valid comparisons can be made. For the purpose of this standard, the upstream limit of an estuary should be defined as the Normal Tidal Limit, but in non-tidal estuaries the upstream limit should be the point beyond which there is no saline influence. The location of a boundary at the seaward limit of transitional waters should take account of the particular geography of each site. Often, geographical features such as deltaic sandbanks, narrow mouth entrances (e.g. lagoons), or discontinuities (breaks) in the coastline create a locally agreed boundary, hence the need for local expertise and agreement. In some areas and countries, consistency has been achieved using a Hbay closing line across the mouth of an estuary although this is diffIcult to determine in widemouthed, funnel-shaped, coastal plain estuaries.
5.3 Procedure for scoring
Annex A sets out guidance on how to allocate scores for each feature category. It contains two separate procedures for scoring — using score band A with quantitative data, or score band B with qualitative data. Score band A (which is used for some of the 23 features) is a 5-point scale (1 = lowest degree of modification, 5 = highest degree of modification). Score band B is a 3-point scale (1, 3, 5; following the same general approach as for score band A).BS/EN 17123-2018 pdf download.
BS/EN 17123-2018 pdf download
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