Development of a GIS Procedure to
Implement a UK Geomorphic Channel Typology
WFD49e
July 2008
EXECUTIVE SUMMARY
Background to research
Both Environment Agency and SEPA have a requirement under the Water
Framework Directive to assess the morphological impacts of
modifications to rivers. Within Scotland this is based on the MImAS
assessment methodology and feeds into the operation of Controlled
Activities Regulations and potentially into the type-specific
Programmes of Measures. One of the key factors in the sensitivity of
rivers is the geomorphic typology of the river, the classification of
rivers based on their morphological attributes. Field surveys of
individual reaches of homogeneous typology is seen as prohibitively
expensive, and despite earlier WFD typologies there is currently no
automated approach to assigning typology from secondary derived
variables. However, an allocation tree developed in an earlier project
WFD49c and a pilot project by Environmental
Systems Research Institute (ESRI) suggested that it would
be possible to create tools for the allocation of river typologies
using an allocation algorithm driven by geomorphic variables extracted
from GIS data.
Objectives of research
The aims of the project were to evaluate the input GIS datasets, ESRI
tools and to develop a specification for the creation of a suite of
open GIS tools within WP1 that could be implemented within EA and
SEPA’s IS infrastructure, while also being flexible enough to
allow changes to input thresholds on which allocation is based.
Different methods of allocating river types were also to be
investigated (e.g. fuzzy logic). Within WP2, the GIS datasets were to
be collated and prepared and GIS tools were to be developed that
extracted various geomorphic parameters and then allocated river
reaches within a series of test catchments. The reach scale typologies
were based on an assumed unmodified channel and the anticipated natural
channel typology, although it is evident that channel modifications
will influence the ability to accurately assign types. Allocated
typologies were then to be subject to validation against field and
other datasets and the algorithms and tools refined where necessary.
Finally, WP3 sought to implement this methodology and to generate
typologies for all Scottish Rivers.
Key findings and recommendations
The GIS data preparation and allocation tool functions to
specification, is intuitive and has been successfully tested and
accepted in the 2 agencies (with any minor incompatibility issues
resolved during installation). The tool was specified to be flexible
and open to amendment, including the potential to modify the decision
tree and data extraction rules and the threshold values used to
distinguish between types.
However, the results are only as good as the input datasets and the
algorithm used to generate the allocation and the conceptual
relationship between the variables selected and the typological
divisions. The original specification identified a range of other
desirable parameters that might have complemented the basic allocation
model, but where the availability of nationally consistent data are
lacking. Inclusion of additional data would also affect the agreed
allocation decision tree which was based on the four core attributes
(geology, slope, confinement and sinuosity). Therefore, the user should
review the comments on data and also consider closely the logic used by
the decision tree.
The project has highlighted the need for additional validation work on
the resulting typology and the potential to add variables to improve on
the typological allocation process.
The validation results confirm that there are some classes which are
very difficult to discriminate in the field (e.g. due to water levels
etc.) and difficult when trying to allocate typologies using secondary
data within the office when the characteristics of the types and
thresholds between types are based on the 4 core variables which
display overlapping ranges.
Detailed breakdowns of the types are given nationally and also by
catchment within the Appendices. The results for Scotland showed that
65% of rivers are allocated to a ‘firm class’ based
on SEPA’s revised decision tree (MImAS types A, B, C, D, F)
with the remaining 35% being allocated to low confidence classes or
where it is expected that the section is subject to partial
modification.
Additional work on the allocation algorithms and the approach to their
application and testing requires refinement. The development and
testing of fuzzy and genetic algorithm based approaches would allow for
the inherent uncertainties related to the classification and threshold
values to be tested.
In addition, exploration of the potential to include additional
parameters (e.g. bed material, stream power etc.) into the allocation
logic is also recommended. There is potential to add predictive level
channel attributes (potentially for bed substrate and stream power) to
build on the current approaches and seek to reduce low confidence
typology allocations.
Keywords:
river typology, GIS, WFD, decision tree
Copies of this report are available from the Foundation, in electronic
format on CDRom at £20.00 + VAT or hard copy at
£15.00, less 20% to FWR members.
N.B.
The report is available for download from the SNIFFER Website