Model Development for Kinkaid Lake
7.1 Basis for pH TMDL
The relationships between pH, chlorophyll "a," and phosphorus were discussed in
Section 18.104.22.168.1. Figures 7-1 and 7-2 show the relationship between chlorophyll "a"
and pH at Kinkaid Lake stations RNC-1 and RNC-3, respectively. The relationships
are only provided at these two locations because samples at stations RNC-2 and
RNC-4 did not show exceedences of the pH standard. As explained in Section
22.214.171.124.1, the figures are expected to show an increase with pH as chlorophyll "a"
increases. Increased chlorophyll "a" concentrations may also lead to low pH values as
the CO2 decreases during respiration. The relationship between chlorophyll "a" and
phosphorus at stations RNC-1 and RNC-3 are shown in Figures 7-3 and 7-4,
respectively. Likewise, these figures are expected to show a direct relationship
between the constituents. The relationships presented in Figures 7-1 through 7-4
provide general trends between model constituents and represent the data available
from sampling. The general relationships shown in Figures 7-1 through 7-4 suggest
that controlling total phosphorus will decrease chlorophyll "a" concentrations, which
will in turn bring pH into the range required for compliance with water quality
standards. The TMDL will be based on the existing relationships
with the knowledge that a larger data set would result in a more
robust TMDL. It is therefore recommended that a TMDL
endpoint of 0.05 mg/L for total phosphorus for Kinkaid Lake be
utilized so that the pH standard is achieved.
7.2 Model Overview
The models used for the TMDL analysis of Kinkaid Lake were
GWLF and BATHTUB. These models require input from several
sources including online databases, GIS-compatible data, and
hardcopy data from various agencies. This section describes the
existing data reviewed for model development, model inputs, and
model calibration and
Schematic 1 shows how the
GWLF model and
BATHTUB model are utilized
in calculating the TMDL. The GWLF model
predicts phosphorus loads from the watershed.
These loads are then inputted in the BATHTUB
model to assess resulting phosphorus
concentrations. The GWLF model outlined in
Schematic 2 shows how GWLF predicts
phosphorus loads from the watershed. The transport
Models used for
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