Civil Engineering Reference
In-Depth Information
holistic approaches require field work, information on flows and technical
and scientific input. The South African Downstream Response to Imposed
Flow Transformation (DRIFT) is also a top-down approach (see King
et al.
2003). Some literature suggests a combination of a 'bottom-up - top-down'
approach would be most useful (Arthington
et al
. 1998, Brizga 2007).
Tidal estuaries and coastal areas require a different form of assessment
again. The issue is not so much water levels and rates of flow as ingress of
saline water from the sea. The sensitivity of the estuary salinity to changes
in dry season flows depends on the hydraulic nature of the system (volumes
of water, depth, level of connection to the sea). Sensitivity to flow regime
indicators can be derived based on general physical characteristics (e.g. see
NSW Office of Water 2011, Appendix 4). Hydraulic models are needed
to predict salinity changes with any degree of confidence, with linkages to
surveys of habitat and information on habitat response to salinity.
In terms of groundwater, the dependency of ecosystems on groundwater is
based on one or more of four regime attributes:
O
flow or flux - the rate and volume of supply of groundwater
O
level - for unconfined aquifers, the depth below surface of the water table
O
pressure - for confined aquifers, the potentiometric head of the aquifer
O
quality - the chemical quality of groundwater expressed in terms of
pH, salinity and/or other potential constituents, including nutrients and
contaminants (SKM 2001).
SKM (2001) proposes a framework for assessing the water regime
requirements, consisting of four steps:
1 identification of potential groundwater-dependent ecosystems
2 analysis of ecosystem dependency on groundwater
3 assessment of water regime in which dependency operates
4 water requirement determination.
They also review a range of tools for addressing each of these steps.
Methods such as those discussed above are well documented and can be
applied, with some adjustments, to cases in any location. However detailed
river-by-river or aquifer-by-aquifer assessments such as these require a level of
expense that is often not available and, where the number of rivers required
to be assessed is large, will exceed the ability of available scientists. For
such cases, lower cost more rapid alternatives are needed, with the option of
applying more intensive approaches to particular rivers where the risks are
greatest.
Some low cost rapid assessments use hydrologic flow statistics to make
recommendations (e.g. protecting flows below the 60th percentile in dry
months). These rely on 'rule of thumb' relationships between flow parameters
and instream habitat and function recommended by experts based on their
