Nonpoint Source Pollution Some basic principles Example study of total pollution loads in the Corpus Christi Bay System rainfall-runoff relationship point and nonpoint source loads connection to bay water quality

Adapt Water to the Land System Water Characterization (water yield, flooding, groundwater, pollution, sediment) Land Characterization (Land use, Soils, Climate, Terrain) Non Point Source Pollution (mean annual flows and pollutant loads)

Possible Land-Water Transform Coefficients The relationships between land and water resources can be characterized by indicator numbers or coefficients, called here transform coefficients because they describe the way a land system transforms the quantity and quality of water as it flows through a landscape. Some examples include: (1) A runoff coefficient, C, specifies the proportion of precipitation that becomes runoff. It can be applied to mean annual or monthly precipitation to determine the corresponding runoff or water yield of a watershed. (2) The Soil Conservation Service Curve Number, CN, (0-100), is a function of land use and soil type that characterizes the amount of flood runoff occuring for a given storm precipitation. (3) Effects of land management on groundwater can be described by the net recharge rate, which is the rate of natural recharge from the land surface to an aquifer, minus the pumping rate of groundwater from the aquifer. (4) Water quality is characterized by the Expected Mean Concentration, (EMC), which is the ratio of pollution load to flow during a runoff period. Pollutant loads are found by taking the product of the EMC and the streamflow rate. (5) The sediment yield of a watershed is measured by the Erosion Rate, or sediment load in a river divided by the upstream drainage area.

Expected Mean Concentration EMC = Load Mass/Flow Volume either on a single event basis or as an annual average L Q C L(t)=Q(t)*C(t) T T T EMC =M/V Flow Concentration Load

Estimating the surface water yield by using a rainfall-runoff function Map-Based Surface Water Runoff Estimating the surface water yield by using a rainfall-runoff function Runoff, Q (mm/yr) Q P Runoff Coefficient C = Q/P Accumulated Runoff (cfs) Precipitation, P (mm/yr)

Water Quality: Pollution Loading Module Load [Mass/Time] = Runoff [Vol/Time] x Concentration [Mass/Vol] Precip. Runoff DEM LandUse Accumulated Load EMC Table Load Concentration

Expected Mean Concentration Land Use EMC Table derived from USGS water quality monitoring sites

Total Constituent Loads Water Quality: Land Surface -Water Body Connection Bay Water Quality Total Constituent Loads Input for Water Quality Model

Readings on Nonpoint Source Pollution (Handbook of Hydrology on reserve in Engr Library) Handbook of Hydrology: Sec 14.1 and 14.2 on nonpoint source pollution sources Handbook of Hydrology: Sec 28.6 on design for water quality enhancement Master’s theses of Christine Dartiguenave http://www.crwr.utexas.edu/gis/gishyd98/library/dartig/rpt97_6.html Ann Quenzer http://www.crwr.utexas.edu/gis/gishyd98/library/quenzer/rpt98_1.html Patrice Melancon http://www.crwr.utexas.edu/crwr/reports/rpt99_3/rpt99_3.html Katherine Osborne http://www.crwr.utexas.edu/crwr/reports/rpt00_10/rpt00_10.htm

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

Purpose To determine the rainfall/runoff relationship To estimate the point and non-point source loads to the bay system To quantify the relationship between the total loads and the bay system water quality

Basic Concept Steady-State Model Water Quality Linkage of Point and Non-point Estimation Total Loads Routing Water Quality Steady-State Model Linkage of the Two Models Calculate Flow and Total Loads

Watershed Delineation Sub-Watersheds

Precipitation = + Merged Precipitation Files Precipitation Trend Oregon State University Precipitation Trend Precipitation Data over Bay System + =

Regression Inputs and Outputs

Surface Water Runoff

Surface Water Runoff + Land Use Precipitation Mean Annual Runoff (mm/ yr ) Land Use + Precipitation

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)

Runoff Into Each Bay System North Bay System 40.5 m3/s 56% of total flow Entire Bay System = 72 m3/s Middle Bay System 24.5 m3/s 34% of total flow South Bay System 7 m3/s 10% of total flow

Bay System Water Balance Entire Bay System

Bay System Water Balance North Bay System Middle Bay System South Bay System

Purpose To estimate the point and non-point source loads to the bay system

Total Constituent Loading Land Surface Load Point Source Load Atmospheric Load ? Sediment Load ?

Land Surface Constituent Loading Load [Mass/Time] = Runoff [Vol/Time] x Concentration [Mass/Vol]

Land Use USGS Land Use (1970’s) Addition of Missing Land Use

Percent Land Use Total Study Area Legend

EMC Table

Point Sources Texas Natural Resources Conservation Commission (TNRCC) Water Quality Segmentation

Loads Routing

Load Routing Methodology

Total Constituent Loads Connection of Both Models Bay Water Quality Total Constituent Loads Input for Water Quality Model

Total Load to Bay System

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

Bay System Segmentation Clipped Segmentation from Drs. Armstrong and Ward Segmentation Used in the CCBNEP Project

Bay System Model Methodology.

Bay System Model Methodology.

Water Quality Analysis Salinity Concentration and Mass Fluxes in Corpus Christi Bay. Finite Segment Analysis Flow of water Transport of Constituents Fluxes Loads Advection Dispersion

Observed vs. Expected Total Nitrogen (mg/l) Total Phosphorus (mg/l)

Observed vs. Expected Oil and Grease (mg/l) Copper (µg/l)

Observed vs. Expected Chromium (µg/l) Zinc (µg/l)

Conclusions Strong South-North gradient in runoff from the land surface Nearly all water evaporates from bays, little exchange with the Gulf Nonpoint sources are main loading source for most constituents Nitrogen, phosphorus, oil & grease loads are consistent with observed concentrations in the bays Metals loads from land account for only a small part of observed concentrations in bays - a reservoir of metals in the bay sediments?