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n Phosphorus
Methodologies will be utilized to complete TMDLs for these constituents:
n Other habitat alterations
n Stream flow alteration
Stream TMDL Modeling
The strategy for completing the watershed/receiving water model TMDLs for the streams in the
Dutchman 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 target goals for TSS,
TSS concentrations must be reduced to
116 mg/L or less. Stream channels are
formed and maintained by the water and
sediment they carry. Channel
equilibrium occurs when a stream's
sediment flow and stream flow are
balanced. That balance can be reflected
qualitatively as Sediment Discharge
times Sediment Particle size is
proportional to the Stream Flow times
the Stream Slope. If one of the four factors change another factor must also change in order for
the stream channel to re-establish equilibrium.
The total sediment load found in the stream channels is a combination of the bed material load
and the suspended load. The bed material load is composed of sediment of the sediment size
found in the streambed. The wash load is composed of the finest size sediment particles and is
usually a function of supply from the watershed. The usual source of wash load is sheet and rill
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
