Environmental Engineering Reference
In-Depth Information
Case example: Judy's Branch, Illinois
a large basin, as a 70% reduction in sediment
load could be achieved through implementation
of all three measures together (VFS, SB and DS in
Fig. 5.9).
Judy's Branch is located near Glen Carbon, Illinois
- across the Mississippi River from St Louis, Mis-
souri. The goal of the HEC-RAS/SIAMapplication
was to assist in identifying sediment management
actions that would enhance habitat quality and
reduce flood damages in a wetland by reducing the
input of sediment to the wetland from Judy's
Branch by 70%. Options to control downstream
sediment delivery included excavating a large ba-
sin to trap sediment entering the wetland, or
controlling the sediment sources upstream, and
HEC-RAS/SIAM was used to investigate the fea-
sibility of source control.
Measures proposed for sediment source control
included: vegetative filter strips (VFS), local sedi-
ment basins (SB), and drop structures (DS). HEC-
RAS/SIAM was used to assess the sediment im-
pacts of these measures, based on 48 sediment
reaches delimited by tributary junctions and
points of significant change in stream hydrology.
Figure 5.9 shows the sediment yield reductions
predicted by HEC-RAS/SIAM for the various
source control measures. The results indicated
that source control was a feasible sediment man-
agement alternative to sediment
Limitations
HEC-RAS/SIAM is a method of accounting for
sediment that, in terms of model complexity and
resource requirements, falls between the semi-
qualitative evaluation generated by Stream Pow-
er Screening and the quantitative routing of
sediment routing that is possible using HEC-
RAS 4.0 or iSIS Sediment. However, its results
lack the precision of a sediment routing model.
When the risks associated with sediment dy-
namics are serious, but limited resources pre-
clude sediment transport modelling, HEC-RAS/
SIAM may add value to purely qualitative anal-
ysis and reduce uncertainty concerning sediment
impacts to a level that is tolerable. It is partic-
ularly useful in fluvial systems where the char-
acteristic behaviour of a significant fraction of
the sediment load switches from that of wash
load to that of bed material load within the
problem or study reach.
trapping in
Fig. 5.9
Annualized sediment yields in Judy's Branch predicted by SIAM (Sediment Impact Analysis Method) for
existing conditions and following implementation of a range of sediment source controlmeasures. DS, drop structures;
SB, small sediment basins; VFS, vegetative filter strips. (See the colour version of this figure in Colour Plate section.)
