city of austin water quality master planning - gis model david maidment francisco olivera mike...
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City of Austin Water QualityMaster Planning - GIS Model
David MaidmentFrancisco Olivera
Mike Barrett Christine
DartiguenaveAnn Quenzer
CRWR - University of Texas
OVERVIEW
The study areaDEM-based topographic
analysisGIS-based hydrologic analysis
The Study Area
LOCATION MAP
LAND USE
WATERSHEDS
EDWARDS AQUIFER
BMP’S
CONTROL POINTS
DEM-Based Topographic Analysis
USGS 7.5’ QUADRANTS OF THE
AUSTIN AREA
DIGITAL ELEVATION MODEL (DEM)
HYDROLOGIC (RASTER-)GIS FUNCTIONS
1
8
4
4
1
16
4
8
1
1
2
4
128
64
1
?
64 N
128 NE
1 E
2 SE
4 S
8 SO
16 O
32 NO
0
1 1
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DEM Flowdirection Flow path
Flowaccumulation 8 directions
FLOW DIRECTION
Water flows to one of its neighbor cells according to the direction of the steepest descent.
Flow direction takes one out eight possible values.
FLOW ACCUMULATION
Flow accumulation is an indirect way of measuring drainage areas (in units of grid cells).
STREAM DEFINITION
All grid cells draining more than 250 cells (user-defined threshold) are part of the stream network.
STREAM SEGMENTATION
Stream segments (links) are the sections of a stream channel connecting two successive junctions, a junction and the outlet, or a junction and the drainage divide.
WATERSHED DELINEATION
All grid cells flowing towards a specific stream segment (link) constitute its watershed or drainage area.
The watershed grid is then converted from raster into vector.
BURNING-IN PROCESS
3.5.c Burnt in DEM
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3.5.a DEM creek 3.5.b Digitized creek
Digitized creek Raised DEM Burnt in DEM
DELINEATED STREAMS OF THE
AUSTIN AREA
DELINEATED WATERSHEDS OF THE
AUSTIN AREA
LOCATION OF CONTROL POINTS
GIS-BasedHydrologic Analysis
VECTOR AND RASTERREPRESENTATIONS OF THE
TERRAIN
Vector representation Raster representation
The parameter represented can be land use, impervious cover,runoff coefficient, EMC...
cell size
IMPERVIOUS COVER VS. LAND USE
Land use Impervious cover (%) Category Code Urban Non urban
Single family 100, 113 40 30 Multi family 200 80 45 Commercial 300 95 60 Office 400 95 60 Industrial 500, 560 95 60 Civic 600 70 30 Park 700 15 5 Transportation 800, 870 100 85 Undeveloped 900, 999 15 5 Water 940 100 100
CURRENT IMPERVIOUS COVER
FUTURE IMPERVIOUS COVER
EQUATION FOR ESTIMATINGANNUAL LOADS
For each land surface cell (30m x 30m):Load [M/T] = Precip [L/T] * Runoff Coeff * Mean Conc [M/L3] *Cell Area [L2]
Load = Direct Runoff Load + Baseflow Load
Use weighted flow accumulation to get downstream loads
In channel, load is adjusted for: groundwater recharge (flow and load decrease) channel erosion (load increase)
Overall loads are adjusted for BMP’s
DIRECT RUNOFF COEFFICIENT VS. IMPERVIOUS COVER
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Impervious Cover
Rv
Data obtained at small watersheds. One point per watershed per storm.
DIRECT RUNOFF COEFFICIENT VS.
IMPERVIOUS COVER
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Impervious Cover
Rv
Non-Recharge Recharge
Data obtained at small watersheds. One point per watershed.
BASEFLOW COEFFICIENT VS.IMPERVIOUS COVER
y = -0.0036x + 0.1904
R2 = 0.902
0.000.020.040.060.080.100.120.140.160.180.20
0 10 20 30 40 50
Impervious Cover (%)
Rs
EMC’S VS. IMPERVIOUS COVER
Estimation of individual storm EMCEstimation of watershed EMCRelating EMC’s with impervious
cover
NH3 CONCENTRATION VS.IMPERVIOUS COVER
y = 0.0024x + 0.1273
R2 = 0.695
0.000
0.100
0.200
0.300
0.400
0.500
0 20 40 60 80 100
Impervious Cover
NH
3 E
MC
, m
g/L
TSS CONCENTRATION VS.IMPERVIOUS COVER
050
100150200250300350400
0.00 0.20 0.40 0.60 0.80 1.00
Impervious Cover
TS
S E
MC
(m
g/L
)
EMC’S VS. IMPERVIOUS COVER
Constituent Direct runoffconcentration
(mg/l)*
Base flowconcentration in
undeveloped areas (mg/l)**
Base flowconcentration indeveloped areas
(mg/l) TSS 190 0 0 BOD C=14(IC)+3.5 0.45 0.8 COD C=98(IC)+18 12 20 TOC C=8.6(IC)+8 2 5 DP C=0.24(IC)+0.04 0.014 0.06 TP C=0.32(IC)+0.19 0.02 0.12
NH3 C=0.24(IC)+0.13 0.02 0.06 TKN C=1.53(IC)+0.13 0.28 0.46 NO3 0.82 0.15 0.6 TN 1.53(IC)+0.95 0.43 1.06 Cu C=0.016(IC)+0.006 NA NA Pb C=0.038(IC)+0.003 NA NA Zn C=0.19(IC) NA NA
VOLUME OF WATERPRODUCED IN EACH CELL
Cell area
Runoff coefficient Precipitation (L/T) Volume of waterproduced by each
cell (L3/T)
Cell area (L2)
MASS OF POLLUTANTPRODUCED IN EACH CELL
EMC (M/L3)Mass of pollutantproduced by
each cell (M/L3)
Volume of water produced by each cell (L3/T)
VOLUME OF WATER LOST FROM EACH
CREEK CELL OF THE RECHARGE ZONE
L = cell size
recharge zone
Creek
LV2
(L/cell) length cell(L) zone recharge in creek of Length
/T)(L recharge creek Total
cell
/TLRecharge
33
FLOW LOST IN THE RECHARGE ZONE
Creek Recharge (cfs)
Creek length (ft)
Recharge perUnit Length
(cfs/ft) Barton 20 37134 5.39E-04 Bear* 9 83758 1.08E-04 Onion 31 58156 5.33E-04 Slaughter 3.5 61333 5.71E-05 Williamson 1.9 57315 3.32E-05
FLOW / LOAD
Volume of water ormass of pollutant
produced by each cell
Drainage area
station
The flow (L3/T) and load (M/T) are calculated with the weighted flowaccumulation function, as the sum of the contributions from theupstream cells.The same process is followed for direct runoff and baseflow.
RunoffΣRechargeΣflow Observed
corrcoef
•For each gauged location (USGS stations), observed flow and predicted flow (after recharge zone correction) were compared.
•For each station, and its corresponding drainage area, a correction factor corrcoef was defined in the following way:
FLOW CALIBRATION
RechargeRunoffcorrcoefflow Observed
FLOW CORRECTION COEFFICIENT
For the ungauged locations, the correction coefficient is extrapolated according to their impervious cover.
Flow correction coefficients
y = -0.0131x + 1.3015
R2 = 0.81690.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
0 10 20 30 40 50 60
ic
coef
Coefficient
Linear (Coefficient)
•For each gauged location (USGS stations), observed load and predicted load (after recharge zone correction) were compared.
•For each station, it was assumed that the difference in load values was produced by channel erosion and a channel erosion coefficient was defined (Kg/yr/ft).
LOAD CALIBRATION
Erosion coefficient(observed load predicted load)
channel length upstream of the station
at the station
LAND-GENERATEDPOLLUTANT
CONCENTRATION
BOD
0
4
8
12
16
20
0 4 8 12 16 20
Measured concentrations [mg/l]
Pre
dic
ted
co
nc
en
tra
tio
ns
[m
g/l]
TSS
0
500
1000
1500
2000
0 500 1000 1500 2000
Measured concentrations [mg/l]P
red
icte
d c
on
ce
ntr
ati
on
s [
mg
/l]
CHANNEL EROSION
TSS Erosion vs. Impervious Cover
y = 2.2629x + 22.836
R2 = 0.6083
0
20
40
60
80
100
120
140
160
180
0 10 20 30 40 50 60
IC (%)
(Ob
se
rve
d l
oa
d -
Pre
dic
ted
Lo
ad
) /
U
ps
tre
am
ch
an
ne
l le
ng
th
•Apply the channel erosion equation to all ungauged watersheds.
• Add the channel erosion to the load at the stations.
CONSTITUENTS THAT INVOLVE
CHANNEL EROSION
Pure land contribution: BOD, COD, DP, NH3, Cu, Pb, Zn.
Land and channel contribution: TSS, TOC, TP, TN.
Construction Load and BMP Effect
CONSTRUCTION LOAD
x % of the area has a development amount of 100%
100 % of the area has a development amount of x%
•EMC(TSS) = 600mg/L•Direct runoff coefficient = 0.5
LOCATED BMP’SDEFINED BY LOAD REMOVAL
BMP grid Removed load grid
cell size
BMPi
Loadi
BMPI+1
LoadI+1
LoadI
LoadI + LoadI+1
WeightedFlowaccumulation
LOCATED BMP’SDEFINED BY REMOVAL
EFFICIENCY
cell value =eff * loadBMP
no data
BMP grid
weightedflowaccumulation
Removed load grid
0
eff*loadBMP
LOCATED BMP’SDEFINED BY REMOVAL
EFFICIENCY
initial loads at BMP’s
BMP2eff2
eff1 * load1
Load2
Total BMP removal
BMP1eff1
eff2 * (load2 - eff1 * load1)
BMP2eff2
BMP1 removal BMP2 removal
Load1 BMP1eff1
NON-LOCATED BMP’S
Barton Springs Zone1 Non-Barton Springs zone Recharge
Zone Contributing
Zone COA Jurisdiction
BMP COA Non-COA
COA Non-COA
Urban2
EasternSuburban
3
WesternSuburban4
Non-COA
ZONE 1 2 3 4 5 6 7 8 NONE 100% 73% 14% 100% SED1 10% SAND2 44% 100% 34% 17% 24% 44% SAND3 10% 62% 56% COMP 36% 36% SOS 20% 20%
NON-LOCATED BMP’S
NON-LOCATED NON-DISCHARGE BMP’S
IC
DirectRunoff Coefficient
Direct Runoff Generated
Nondischarge
BMPs
Effective DirectRunoff
Effective Direct Runoff Coefficient
Effective IC
Effective IC is used for calculating channel erosion.
CONCLUSIONS
The goal of this research project was to determine current and future non-point source pollution loads in Austin streams.
The model aims at being as flexible as possible: The BMP parameters and the EMCs can be easily modified and they do not
require the analyst to recalibrate the model Modification of the current land use conditions, of the precipitation value used, or
of the impervious cover/runoff coefficient relationships will require recalibration of the model
The effects of both located and non-located BMP’s, and of construction activities were modeled.
Current flows matching observed flows at 17 USGS stations were determined
Loads were established for 122 sites (Environmental Integrity Index sites, USGS stations and mouths) within the study area.
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