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Published byGodwin Barker Modified over 9 years ago
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Total Loads and Water Quality in the Corpus Christi Bay System Presented by: Ann Quenzer and Dr. David Maidment Special Thanks: Corpus Christi Bay National Estuary Program Ferdinand Hellweger Dr. Nabil Eid Dr. George Ward Dr. Neal Armstrong
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Purpose u To determine the rainfall/runoff relationship u To estimate the point and non-point source loads to the bay system u To quantify the relationship between the total loads and the bay system water quality
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Basic Concept Point and Non-point Estimation Total Loads Routing Water Quality Calculate Flow and Total Loads Linkage of the Two Models Steady-State Model
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Purpose u To determine the rainfall/runoff relationship
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Watershed Delineation Sub-Watersheds
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Precipitation + = Precipitation Trend over Bay System Merged Precipitation Files Oregon State University Precipitation Data
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Regression Inputs and Outputs
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Surface Water Runoff
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Mean Annual Runoff (mm/yr) Land Use + Precipitation
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Precipitation and Runoff Gradient Precipitation and Runoff Gradient from South (A) to North (B) along the Bay System Precipitation and Runoff Gradient Locations in the South (A) and North (B)
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Runoff Into Each Bay System Middle Bay System 24.5 m 3 /s 34% of total flow Entire Bay System = 72 m 3 /s North Bay System 40.5 m 3 /s 56% of total flow South Bay System 7 m 3 /s 10% of total flow
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Bay System Water Balance Entire Bay System
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Bay System Water Balance North Bay System Middle Bay System South Bay System
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Purpose u To estimate the point and non-point source loads to the bay system
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Total Constituent Loading Land Surface Load Point Source Load Atmospheric Load ? Sediment Load ?
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Land Surface Constituent Loading Load [Mass/Time] = Runoff [Vol/Time] x Concentration [Mass/Vol]
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Land Use USGS Land Use (1970’s) Addition of Missing Land Use
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Percent Land Use Total Study Area Legend
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EMC Table
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Point Sources Texas Natural Resources Conservation Commission (TNRCC) Water Quality Segmentation
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Loads Routing
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Elevation Grid Modification Methodology
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Model Connection Methodology
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Load Routing Methodology
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Total Constituent Loads Input for Water Quality Model Connection of Both Models Bay Water Quality
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Total Load to Bay System
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Load Sources
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Load Contribution
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Atmospheric Contribution Total Nitrogen Atmospheric Load to Land Surface = 2,700 Kg/d which is 35% of Land Surface Load from agricultural land use. This calculation is made assuming the EMC of 4.4 mg/l for agriculture and a Nitrogen concentration of 1.1 mg/l in precipitation
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Purpose u To quantify the relationship between the total loads and the bay system water quality
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Bay System Segmentation Segmentation Used in the CCBNEP Project Clipped Segmentation from Drs. Armstrong and Ward
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Bay System Model Methodology.
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Water Quality Analysis Salinity Concentration and Mass Fluxes in Corpus Christi Bay. Fluxes Flow of water Advection Dispersion Loads Transport of Constituents Finite Segment Analysis
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Observed vs. Expected Total Phosphorus (mg/l) Total Nitrogen (mg/l)
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Observed vs. Expected Oil and Grease (mg/l)Copper (µg/l)
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Observed vs. Expected Zinc (µg/l)Chromium (µg/l)
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T-Test Results
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Decay Rates (using three segment model)
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Provisional EMC Data Original EMC Values from USGS Study (Baird, 1996) Total Nitrogen= 4.40 mg/l Total Phosphorus= 1.30 mg/l Provisional EMC Values from Agricultural Runoff Studies at King Ranch and Agricultural Field Near Edroy, TX (Mean Values Obtained from Okerman of USGS) Total Nitrogen= 1.49 mg/l Total Phosphorus= 0.47 mg/l
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Provisional EMC Values Total Nitrogen and Total Phosphorus from Land Surface Sources to Bay System Using Original and Provisional EMC Values. Total Nitrogen Reduction = 54% Total Phosphorus Reduction = 60%
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Provisional EMC Values Total Nitrogen and Total Phosphorus from All Sources to Bay System Using Original and Provisional EMC Values. Total Nitrogen Reduction = 27% Total Phosphorus Reduction = 38%
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Provisional EMC Values
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Conclusions u Strong South-North gradient in runoff from the land surface u Nearly all water evaporates from bays, little exchange with the Gulf u Nonpoint sources are main loading source for most constituents u Nitrogen, phosphorus, oil & grease loads are consistent with observed concentrations in the bays u Metals loads from land account for only a small part of observed concentrations in bays - a reservoir of metals in the bay sediments?
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