total loads and water quality in the corpus christi bay system presented by: ann quenzer and dr....
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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 ProgramFerdinand HellwegerDr. Nabil EidDr. George WardDr. 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
Point and Non-pointEstimation
Total LoadsRouting
WaterQuality
Calculate Flowand Total Loads
Linkage of the Two Models
Steady-State Model
Purpose
To determine the rainfall/runoff relationship
Watershed Delineation
Sub-Watersheds
Precipitation
+ =
Precipitation Trendover Bay System
Merged Precipitation Files
Oregon State UniversityPrecipitation Data
Regression Inputs and OutputsWat er sh ed St r eamf l ow Pr ecip i t at i on %A g r i c %Ran g e
( mm/ y r ) ( mm/ y r )L os Omos 4. 07 618. 25 12. 24 87. 21Ch i l t i p i n 105. 80 841. 17 86. 40 10. 92San Fer n an d o 12. 36 661. 08 22. 09 76. 53San Dieg o 7. 65 664. 78 13. 29 85. 63Oso 112. 64 774. 75 96. 87 0. 97A r an sas 46. 03 809. 99 58. 07 37. 91Missi on 73. 51 846. 89 25. 22 73. 04Med io 29. 14 786. 75 40. 82 58. 30Cop an o 163. 90 927. 41 6. 56 66. 80
W ater
Q = 0
UrbanQ = 0.24 * P
where: Q = runoff depth (mm/yr)P = precipitation depth (mm/yr)
Q = 0.008312 * exp ( 0.011415 * P )
where: Q = runoff depth (mm/yr)P = precipitation depth (mm/yr)0.008312 = exp (-4.79004056)
Agriculture
Range Land, Barren, Forest Land, Other Q = 0.0053 * exp ( 0.010993 * P )
where: Q = runoff depth (m m/yr)P = precipitation depth (mm/yr)0.0053 = exp (-5.239702)
Surface Water RunoffPrecipitation vs. Runoff Curves
Chiltipin
Copano
Oso
Mission
AransasMedioSan Diego
Los OmosSan Fernando0.00
50.00
100.00
150.00
200.00
250.00
0 200 400 600 800 1000
Depth of Precipitation (mm/yr)
De
pth
of
Ex
pe
cte
d R
un
off
(m
m/y
r)
Range LandAgriculture
Urban
Stations
Land Use
+Precipitation
Surface Water RunoffPrecipitation vs. Runoff Curves
Chiltipin
Copano
Oso
Mission
AransasMedioSan Diego
Los OmosSan Fernando0.00
50.00
100.00
150.00
200.00
250.00
0 200 400 600 800 1000
Depth of Precipitation (mm/yr)
De
pth
of
Ex
pe
cte
d R
un
off
(m
m/y
r)
Range LandAgriculture
Urban
Stations
Mean AnnualRunoff (mm/yr )
Land Use+
Precipitation
Precipitation and Runoff Gradient
Precipitation and Runoff Gradients along Bay System
BA
B
A
1
10
100
1000
South North
Pre
cipi
tatio
n (m
m/y
r)
Precipitation
Runoff
Precipitation and Runoff Gradient fromSouth (A) to North (B) along the Bay System
Precipitation and Runoff GradientLocations in the South (A) and North (B)
Runoff Into Each Bay System
Middle Bay System24.5 m3/s34% of total flow
Entire Bay System = 72 m3/s
North Bay System40.5 m3/s56% of total flow
South Bay System7 m3/s10% of total flow
Bay System Water Balance
-150.0
-100.0
-50.0
0.0
50.0
100.0
150.0
Precip Evap Runoff Inflowfrom other
bays
Outflow tootherbays
Net Flow
Water Source
Entire Bay System
Bay System Water Balance
-80.0
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
80.0
Precip Evap Runoff Inflow fromother bays
Outflow toother bays
Net Flow
W ater Source
Flow
(m^3
/s)
-80.0
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
80.0
Precip Evap Runoff Inflowfrom other
bays
Outflow tootherbays
Net Flow
W ater Source
-80.0
-60.0
-40.0
-20.0
0.0
20.0
40.0
60.0
80.0
Precip Evap Runoff Inflow fromother bays
Outflow toother bays
Net Flow
Water Source
Flow
(m̂3/
s)
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 LoadPoint Source Load
Atmospheric Load
Total Loads
Nueces River Load
? Sediment Load ?
Land Surface Constituent Loading
Load [Mass/Time] = Runoff [Vol/Time] x Concentration [Mass/Vol]
Land U se
EMC Table
Concentration
RunoffLoad
Land UseUSGS LandUse (1970’s)
Addition ofMissingLand Use
Updated LandUse from theTexas Parkand Wildlife
Percent Land Use
Total Study Area
Legend
North Portionof the Study Area
Middle Portionof the Study Area
South Portionof the Study Area
EMC Table
Constituent Res Comm Ind Trans Agr Range UndevTotal Nitrogen (mg/l) 1.82 1.34 1.26 1.86 4.40 0.70 1.50Total Phosphorus (mg/l) 0.57 0.32 0.28 0.22 1.30 <0.01 0.12Oil and Grease (mg/l) 1.7 9.0 3.0 0.4Copper (ug/l) 15.0 14.5 15.0 11.0 1.5 <10Chromium (ug/l) 2.1 10.0 7.0 3.0 <10 7.5Zinc (ug/l) 80 180 245 60 141 16 6
Point Sources
Texas Natural ResourcesConservation Commission (TNRCC)Water Quality Segmentation
Loads Routing
DEM StreamsModify DEM toBurn in Streams
Connect Streams to Bay System
Flow DirectionFlow Accumulation
Elevation Grid Modification Methodology
ORIGINAL ELEVATIONMODIFIED ELEVATION
KNOWN STREAM LOCATIONAND STREAM DELINEATEDFROM MODIFIED ELEVATION
GRID CELL SIZESECTION A-A
STREAM DELINEATEDFROM ORIGINAL ELEVATION
ELEVATIONRESOLUTION
GRIDCELL SIZE
PLAN
AA
Model Connection Methodology
OCEANLAND SURFACE BAY
SEGMENTSINK
ELEVATION
MSL
SECTION
PLAN
CENTROID
FLOW PATH
Load Routing Methodology
67 56 49 46 50
53 44 37 38 48
58 55 22 31 24
61 47 21 16 19
53 34 12 11 12
2 2 4 4 8
1 2 4 8 4
128 1 2 4 8
2 1 4 4 4
1 1 1 2 16
0 0 0 0 0
0 9 17 40 0
0 0 93 0 16
0 0 1 0
0 0 5 8
ELEVATION
FLOW DIRECTION
ACCUMULATED FLOW
4 5 12 17 23
3 3 10 12 16
2 2 6 8 10
0 1 4 7 8
0 0 3 4 7
LOAD
133
163
Total Constituent Loads
Input for WaterQuality Model
Connection of Both Models
Bay Water Quality
Total Load to Bay System
Percent Load for Each ConstituentTotal Load = 21,000 Kg/d
Total Nitrogen
Total Phos
Oil & Grease
Total Metals
Load Sources
0%
20%
40%
60%
80%
100%
TotalNitrogen
TotalPhosphorus
Oil andGrease
Copper Chromium Zinc
Nueces
Land
Point
Atmo
Load Contribution
0%
20%
40%
60%
80%
100%
TotalNitrogen
TotalPhosphorus
Oil andGrease
Copper Chromium Zinc
South
Middle
North
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 agricultureand a Nitrogen concentration of 1.1 mg/l in precipitation
Purpose
To quantify the relationship between the total loads and the bay system water quality
Bay System Segmentation
Segmentation Used inthe CCBNEP Project
Clipped Segmentation fromDrs. Armstrong and Ward
Bay System Model Methodology.
WA
E (s s )A,B A B· –
Q sA,B A·
WB
E (s s )B,BND B BND· –
Q sB,BND B·
SEGMENT A
VA, KA, sA
BOUNDARY
sBND
SEGMENT B
VB, KB, sB
·K VA A· sA ·K VB B
· sB
E (s s )O,A O A· –
Q sO,A A·
Bay System Model Methodology.
dsB * VB = QA,B*sA - QB,BND*sB + EA,B*(sA - sB) + EBND,B*(sBND - sB) - KB*VB*sB + WB
dt
where: dsB = change in concentration of segment B / change in timedtVB = volume of segment B; (m3)QA,B = flow from segment A to B; (m3/s)QB,BND = flow from segment B to BND; (m3/s)sA = concentration of constituent in segment A; (mg/l)sB = concentration of constituent in segment B; (mg/l)sBND = concentration of constituent at boundary; (mg/l)EA,B = bulk dispersion coefficient between segments A,B; (m3/s)EB,BND = bulk dispersion coefficient between segments B,BND; (m3/s)KB = decay rate in segment B; (/d)WB = waste load in segment B; (kg/yr)
Water Quality Analysis
Salinity Concentration and Mass Fluxes in Corpus Christi Bay.
Fluxes
Flow of water
Advection
Dispersion
LoadsTransport of Constituents
Finite SegmentAnalysis
Observed vs. Expected
Total Phosphorus (mg/l)Total Nitrogen (mg/l)
Observed vs. Expected
Oil and Grease (mg/l) Copper (µg/l)
Observed vs. Expected
Zinc (µg/l)Chromium (µg/l)
T-Test Results
Constituent Bay System Average t-testTotal Nitrogen North -18.2
Middle -14.5South -8.2Total -14.2
Total Phosphorus North -33.1Middle -21.9South -7.5Total -23.8
Oil and Grease North -0.1Middle -1.0SouthTotal 0.0
Copper North 4.6Middle 2.6South 1.1Total 3.0
Chromium North 10.0Middle 5.2South 2.3Total 6.4
Zinc North 1.9Middle 3.2South 1.4Total 2.7
Decay Rates (using three segment model)
K = ( QN,M*sN – QM,S* sM – QM,Oc*sM + EN,M(sN-sM) + EOc,M(sOc-sM) + ES,M(sS-sM) + WM ) / ( VM*sM )
where: K = the decay rateQN,M*sN = Advective load from the north segmentQM,S* sM = Advective load leaving the middle segment to the
south segmentQM,Oc* sM = Advective load leaving the middle segment to the
oceanEN,M(sN-sM) = dispersive load between the north and middle
segmentsEM,Oc(sM-sOc) = dispersive load between the middle segment
and the oceanEM,S(sM-sS) = dispersive load between the middle and south
segmentsWM = waste load entering the middle segmentVM*sM = load volume in the segment
Decay Rates (using three segment model)
Constituent Bay Decay Rate Ave DecaySection ( /d ) Rate ( /d )
Total Nitrogen North 0.030Middle 0.011South 0.024 0.022
Total Phosphorus North 0.013Middle 0.004South 0.009 0.009
Provisional EMC Data
Original EMC Values from USGS Study (Baird, 1996)
Total Nitrogen = 4.40 mg/lTotal 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/lTotal Phosphorus = 0.47 mg/l
Provisional EMC ValuesTotal Nitrogen and Total Phosphorus from Land Surface Sources to Bay System Using Original and Provisional EMC Values.
Total Nitrogen Total PhosphorusOriginal Provisional Original Provisional
Segment (Kg/d) (Kg/d) (Kg/d) (Kg/d)
North 5021.27 2268.98 1283.48 498.46Middle 1184.66 530.17 338.45 151.78South 1412.24 669.7 356.19 144.38Total 7618.17 3468.85 1978.12 794.62
Total Nitrogen Reduction = 54%
Total Phosphorus Reduction = 60%
Provisional EMC ValuesTotal Nitrogen and Total Phosphorus from All Sources to Bay System Using Original and Provisional EMC Values.
Total Nitrogen Reduction = 27%
Total Phosphorus Reduction = 38%
Total Nitrogen Total PhosphorusOriginal Provisional Original Provisional
Segment (Kg/d) (Kg/d) (Kg/d) (Kg/d)
North 6576.35 3824.06 1409.7 624.68Middle 4025.84 3371.35 1203.25 1016.58South 4566.3 3823.76 496.37 284.56Total 15168.49 11019.17 3109.32 1925.82
Provisional EMC Values
T o ta l N itro ge n C o nc e ntra tio ns
O rig in a l P ro v is io n a lS e g m e n t e x p (m g /l) e x p (m g /l) o b s (m g /l)N o r th 0 .5 5 0 .3 4 0 .1 9M id d le 0 .3 3 0 .3 2 0 .2 2S o u th 0 .2 3 0 .2 1 0 .1 8
Total Phosphorus C onc entrationsOriginal Provisional
Segm ent exp (m g/l) exp (m g/l) obs (m g/l)North 0.20 0.12 0.08Middle 0.15 0.13 0.13South 0.09 0.08 0.07
Provisional EMC Values
Constituent Bay Decay Rate Decay RateSegment Original (/d) Provisional (/d)
Total Nitrogen North 0.030 0.017Middle 0.011 0.009South 0.024 0.021Average 0.022 0.016
Total Phosphorus North 0.013 0.005Middle 0.004 0.003South 0.009 0.008Average 0.009 0.005
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?