1. 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

2. 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)

3. 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.

4. 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

5. 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)

6. 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

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

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

9. 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
Ann Quenzer
Patrice Melancon
Katherine Osborne

10. 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

11. 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

12. 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

13. Watershed Delineation
Sub-Watersheds

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

15. Regression Inputs and Outputs

16. Surface Water Runoff

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

18. 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)

19. 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

20. Bay System Water Balance
Entire Bay System

21. Bay System Water Balance
North Bay System
Middle Bay System
South Bay System

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

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

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

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

26. Percent Land Use
Total Study Area
Legend

27. EMC Table

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

29. Loads Routing

30. Load Routing Methodology

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

32. Total Load to Bay System

33. 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

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

35. Bay System Model Methodology.

36. Bay System Model Methodology.

37. 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

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

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

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

41. 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?