DRAFT Page 2 of 2
n Silver
n Salinity/TDS/Chlorides
Methodologies will be utilized to complete the TMDL for other habitat alterations.
Stream TMDL Modeling
The strategy for completing the watershed/receiving water model TMDLs for the streams in the
Bonnie Creek Watershed is shown in Figure 1. This approach allows a linkage between source
and endpoint resulting in an allocation to meet water quality standards. After loads are
predicted, concentrations resulting from
the loads will be compared to the TMDL
endpoints. If the concentration predicted
is greater than the endpoint, the TMDL
for the constituent of concern will be
considered runoff driven and allocations
will be distributed accordingly. This
assumes that the majority of streamflow
is derived from runoff, not baseflow. If
the concentration predicted is less than
the endpoint, the TMDL for the
constituent of concern will be treated as
baseflow driven.
Stream TMDL Methodologies
To meet Illinois EPA goals for full
support for habitat alterations, 70 percent
of the stream bank surfaces must be
covered by vegetation or rock, there
must be no extensive recent or regularly
maintained channelization present, and
the stream must have recovered from
older channelization projects. To develop
TMDLs for habitat alterations, visual
inspection using aerial photography and
field visit information will be utilized to
recommend plans to address channel downcuttting and a bank vegetation plan.
Progress to Date and Next Steps for TMDL Development
Methodologies and models to address TMDLs in the Bonnie Creek Watershed have been
outlined. CDM also prepared for a public meeting held in December 2001 for the watershed.
The next steps include conducting the public meeting and then conducting the modeling and
methodology analyses needed to support TMDL development.
Figure 1
Strategy for Stream TMDL Modeling
Concentration in Runoff
Greater
than Endpoint?
Concentration in Runoff
Greater
than Endpoint?
PPrereddicict tL Looaaddininggss
CCoommppaarree t too EEnnddppooiinnttss
Runoff
Driven
Runoff
Driven
Baseflow
Driven
Baseflow
Driven
AAllloloccaattioionn
Steady State
Water
Quality Model
Steady State
Water
Quality Model
AAllloloccaattioionn
Yes No
Consider
De-listing
Consider
De-listing
