Flows and Transport in Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 122

• Stage 3. Measures Appraisal Process: for waterbodies where lows are not supporting

the WFD objective of GES (Figure 4.33), this process includes the implementation of a
Restoring Sustainable Abstraction (RSA) program study and ultimately the development
of a river basin management plan (RBMP) to set out the actions, or a program of measures,
to ensure that these waters achieve WFD by 2015 and that there is no deterioration from
their current status.

One of the components of the RSA program study is the participation of interested parties
through a catchment stakeholder group and a RAM framework (Dyson et al. 2008), based on the
assessment of four elements of the ecosystem: physical character, isheries, macrophytes, and mac-
roinvertebrates. Since the sensitivity of the ecosystem to reduced lows is related to the environmen-
tal low needs of any river, rivers are given a low status in the form of a RAM score from 1 to 5
(1 being the least sensitive to the reduction in low and 5 being the most sensitive to the reduction
in low). Physical character is determined by comparing the river with photographs of typical river
reaches in each class. Fisheries are determined by the expert opinions of environmental agency
isheries staff to classify the river according to the description of each of the RAM score classes.
Macroinvertebrates and macrophytes scores are determined by using low-sensitive metrics, such as
LIFE scores. For example, in terms of physical character, rivers with steep slopes and/or wide shal-
low cross sections have a RAM score of 5, since very little low reduction is needed to change the
wetted perimeter of the cross section. Lowland river reaches that are narrow and deep have a RAM
score of 1 (Acreman et al. 2003).
Once the scores have been determined, rivers are then categorized into one of ive environmental
weighting bands: Band A (most sensitive), Band B, Band C, Band D, and Band E (least sensitive).
In a separate part of the RAM framework, a low duration curve is produced where different allow-
able abstraction points can be found from this curve. The percentages of natural Q95 lows can be
abstracted from the different bands, but more detailed methods, such as habitat modeling, are rec-
ommended where environmental lows need to be deined in more detail. The low duration curve
produced by the RAM framework focuses on ecologically acceptable lows and contains many
characteristics of the low regime. While the RAM framework contains the basic magnitudes of
droughts, low lows, and loods, it does not retain characteristics such as temporal sequencing and
the duration or timing of lows (Acreman et al . 2003). According to Acreman et al . (2003), an eco-
logically acceptable low duration curve is most appropriate where the river ecosystem is controlled
by the seasonal characteristics of dry season/wet season or winter/summer lows.

4.6.2.4.3 DRIFT
A notable example of a holistic environmental low methodology is DRIFT, a scenario-based inter-
active approach to EFAs, in which a database is created that can be queried to describe the biophysi-
cal consequences of any number of potential future low regimes (scenarios).
The DRIFT methodology focuses on identifying river water levels associated with a particular
set of biophysical functions and speciic hydrological and hydraulic characteristics. Similar to
BBM, DRIFT uses multidisciplinary specialists to describe the consequences of reducing dis-
charges through identiied low regimes in terms of a deterioration in biotic and abiotic conditions
(King et al. 2008). DRIFT details and quantiies the links between changing river conditions and
the social and economic impacts to those that rely on the river for subsistence. Acreman et al.
(2003) state, “Probably it's most important and innovative feature is a strong socio-economic mod-
ule, which describes the predicted impacts of each scenario on subsistence users of the resources
of a river.”
According to Brown and King (2000), the central idea behind DRIFT is that the various aspects
of the river low regimes result in different responses from the river ecosystem. The removal of all
or part of an element in the river low regime will have an effect on the river ecosystem differently
than the removal of some other element.