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Methodology and Modeling Approach for Streams
For the Big Muddy River #1 Watershed, TMDLs for the following constituents will be
completed using a watershed/receiving water model combination:
n DO
n Manganese
n Sulfates
n Salinity/TDS/Chlorides
n Nitrogen
n Cyanide
Methodologies will be utilized to
complete TMDLs for these constituents:
n pH
n TSS
n Siltation
Stream TMDL Modeling
The strategy for completing the
watershed/receiving water model
TMDLs for the streams in the Big
Muddy River #1 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
Figure 6-1
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
