Central Coast Ambient Monitoring Program
(CCAMP)
Stream Flow Estimation Model v 1.1
All models are wrong, some models are useful
Abstract:
Words go here
Introduction:
Since the origination of CCAMP in 1998 the need to quantify stream flows, pollutant
loads, and risk factors related to beneficial uses of water has been a continuing issue that
CCAMP staff has addressed at various levels of detail and effort over the years. Early
efforts involved estimations of risk factors utilizing generalized estimations of freshwater
flow and other potential risk factors, based on a sixty year record of precipitation (need
cite) patterns and various watershed characteristics. The next level of development
incorporated a simple exponential dilution model to address the mixing of freshwater
outflows with near shore ocean waters and assign explicit risk estimations for each near
shore area as defined by the ATOS grid (one half kilometer square sections along the
coast(need cite)). The next level began to address the issue of time and incorporated
detailed precipitation characterizations such as the amount of rainfall during the last day,
the last 3 days, the last 5 days, etc. The next level, presented herein, incorporated
methods of risk attribution on a daily basis to begin the process to more explicitly address
multiple sources of risk.
Methods:
The CCAMP model was created because existing models did not provide sufficient
spatial or temporal resolution for the intended uses. The modeling approach employed
aspires to enhance stream flow information presented within the National Hydrography
Dataset Plus (NHD+) geospatial framework. The CCAMP model ‘tunes’ the unit runoff
model (UROM) estimates provided in NHD+ to provide higher spatial and temporal
resolution. The UROM estimates in NHD+ provide annual average daily flows for each
stream reach (NHD medium resolution hydrography). The CCAMP model provides an
estimation of flow at the downstream point of a given stream reach on a given day.
The underlying NHD+ approach uses five USGS stream gages from the Hydro-Climatic
Data Network (HCDN) within a 200 mile radius as calibration gages to produce a useful
level of generalization in estimation of average annual daily flows.
In the creation of the CCAMP model, a number of issues were taken into consideration,
such as:
1) The diversity of California hydrologic climate regimes exist at a substantially smaller
spatial scale than the 200 mile radius presented by the NHD+ Unit Runoff Method.
Development working notes only: Do not cite or reference.
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2) Characterization of anthropogenic influences on stream and river flows was beyond
the scope of the NHD+ effort. (e.g. scheduled releases from impoundments, groundwater
extractions being converted to surface flows)
3) USGS Gage network measurements provide high temporal data density and low spatial
data density.
4) Stream transect method measurements provide high spatial data density and low
temporal data density.
Much of the following text is excerpted from NHD+ Documentation
NHD+ Flow Estimates
NHD+ incorporates two methods for estimating mean daily flow for each flowline.
Values for the attribute “MAFlowU” are based on the Unit Runoff Method (UROM),
which was developed for the National Water Pollution Control Assessment Model
(NWPCAM) (Research Triangle Institute, 2001). Values in “MAFlowV” are based on
methods from Vogel et al., 1999. Values provided which are based on the Vogel method
are far less complete in NHD+ than those provided based on the UROM method.
Accordingly, the UROM method values are incorporated in the CCAMP model.
NHD+ UROM flow estimates are based on use of the Hydro-Climatic Data Network
(HCDN) of gages. These gauges are usually not affected by human activities, such as
major reservoirs, intakes, and irrigation withdrawals; thus, the mean annual flow
estimates are most representative of “natural” flow conditions. The estimation method
used the HCDN gages because each method is developed for use at large scales; for
instance, Hydrologic Regions. It was beyond the scope and capabilities of both UROM
and Vogel methods to determine the human-induced effects at this scale.
UROM Flow Estimates
The UROM flow estimates use flowline catchment area estimates and unit runoff
(cfs/km2) data from associated watersheds (i.e., 8-digit Subbasin). The USGS stream
gages in HCDN were selected for developing the unit runoff values because those gages
represent relatively natural hydrologic conditions and are not influenced by controlled
releases from reservoirs. Further, only gages with a drainage area less than the drainage
area of the 8-digit Subbasin where the gage is located were selected, so that the discharge
data represents runoff for only that Subbasin. For instance, a gage on the Mississippi
River at St. Louis is not representative of the unit runoff from that Subbasin. At the
national level, a total of 1,338 HCDN gages were identified for this dataset.
Based on the drainage area comparisons, the dataset of 1,338 HCDN gages and the
dataset of associated stream discharge data for these gages were used to derive mean
annual and mean summer unit runoffs (ft3/sec/km2) for each 8-digit Subbasin. The nearest
Development working notes only: Do not cite or reference.
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HCDN gages were identified using a 200 mile maximum search radius from the centroid
of an 8-digit Subbasin. In most Subbasins, five gauges were selected, but some had fewer
than five within the 200 mile search radius. Mean annual and mean summer unit runoffs
for each 8-digit Subbasin were calculated using a weighted-average technique based on
the square of the distance of the selected HCDN gages from the centroid of the Subbasin.
Development working notes only: Do not cite or reference.
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The computations are defined as follows:
QCU_MA = Σ(QHCDN_MA × 1/D2CU_HCDN)/Σ(1/D2CU_HCDN)
where
QCU_MA
QHCDN_MA
D2CU_HCDN
= estimated mean annual unit discharge for the 8-digit
Subbasin of interest,
= mean annual unit discharge for the selected HCDN gage,
and
= square of distance from the selected HCDN gage to the
centroid of the 8-digit Subbasin of interest.
IncrFlowU is the incremental flow at the bottom of the flowline, computed as
IncrFlowU = A * CU_MA
where
A
= Drainage Area of the catchment (km2), and
CU_MA = Unit Runoff for the 8-digit Subbasin (cfs/ km2).
The UROM-based mean annual flow for each flowline (MAFlowU) is computed as
∑ i=1 to n (IncrFlowUi).
NHD+ UROM “Tuning” Using Intermittent Flow Adjustment Factors
The development of the UROM was done as part of the development of NWPCAM
(Research Triangle Institute, 2001). For Hydrologic Regions west of the Mississippi,
initial NWPCAM estimates of routed discharge generally were observed to be greater
than the HCDN gage values. Consequently, for the Western Hydrologic Regions, a
method was developed to better match (quasi-calibrate) discharge estimates to observed
data. The discharge estimates were lowered by incorporating only a percentage of the
stream segment-specific runoff for intermittent segments. The method calculates
discharge estimates assuming various contributions (e.g., 100, 50, 25, 10, and 1 percent)
of the unit runoff for intermittent flowlines. This method proved successful in improving
the match between gage flows and UROM-based flow estimates. The method is
employed in the Western Hydrologic Regions in NHDPlus. The best fit is selected based
on graphical analyses that compare the UROM flow estimates to the gaging data. As
NHD+ is produced, this tuning process will be completed in each Hydrologic Region
west of the Mississippi (Regions 9, 10, 11, 12, 13, 14, 15, 16, 17, and 18). In Hydrologic
Region 17, an intermittent unit runoff contribution of 10 percent appears to work best and
is included as the UROM estimates in the distribution datasets.”
Development working notes only: Do not cite or reference.
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CCAMP UROM “Tuning” Using Local Gages.
For each monitoring site from one to three USGS gages believed to represent local flow
conditions were selected. The objective of gage selections is to provide a more localized
characterization of runoff conditions than that provided by the NHD+ UROM method.
Optimum characterization is accomplished through selecting gages which are thought to
be most representative of meteorological characteristics and anthropogenic influences
pertaining to the stream reach being modeled.
Model Ground Truth and Performance Evaluation Procedure
A team of CCAMP field samplers have been contemporaneously measuring a variety of
water quality analytes and flow at sites throughout central California. For each
monitoring site we compared flow measured using the stream transect method (STM)
with each modeled flow. The Benchmark for model performance used was the
correlation between model predicted flows and stream transect method measured flows.
Dataset Preprocessing Procedure
Create GIS coverage of monitoring sites from latitude, longitude information
Create temporary NHD+ hydrography coverage with coastline features removed
Perform spatial join of monitoring sites to NHD+ catchments
Perform manual editing of assignments of NHD+ Comid’s to monitoring sites
Create GIS coverage of USGS sites from latitude, longitude information
Perform spatial join of USGS sites to NHD+ catchments
Perform manual editing of assignments of NHD+ Comid’s to USGS sites
Perform tabular data join between monitoring sites and reach attributes tables of NHD+
using NHD+ Catchment Comid as primary key. Export resulting table to delimited file
for database processing.
Perform tabular data join between USGS sites and reach attribute tables of NHD+ using
NHD+ Comid as primary key. Export resulting table to delimited file for database
processing.
Model Initialization Procedure (Professional Judgment based parameterization)
Select from one to three USGS gages believed to represent local flow conditions for each
monitoring site. The objective of gage selection is to provide a more localized
characterization of runoff conditions than that provided by the NHD+ UROM method
which employs 5 gages within a 200 km radius of the subject reach. Optimum
characterization is accomplished through selecting gages which are thought to be most
representative of meteorological characteristics and anthropogenic influences pertaining
to the stream reach being modeled.
Development working notes only: Do not cite or reference.
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Model Runtime Procedure (algorithm)
Cautionary notes related to NHD+ flow estimates under 5 cfs contained in the NHD+ documentation
motivated us to create slightly different models for two flow regimes.
The following procedure is executed for each reach of interest (subject_reach) and for each day during the
time period of interest:
‘used for flows => 5 cfs
flow_ratio[1] = gage_flow[1] / NHD_reach_mean_daily_flow[1]
flow_ratio[2] = gage_flow[2] / NHD_reach_mean_daily_flow[2]
flow_ratio[3] = gage_flow[3] / NHD_reach_mean_daily_flow[3]
mean_flow_ratio=( flow_ratio[1]+ flow_ratio[2]+ flow_ratio[3]) / reach_count
flow_estimate[subject_reach]= mean_flow_ratio * reach_mean_daily_flow[subject_reach]
‘used for mean daily flows under 5 cfs
flow_ratio[1] = gage_flow[1] / NHD_reach_cumulative_drainage_area[1]
flow_ratio[2] = gage_flow[2] / NHD_ reach_cumulative_drainage_area[2]
flow_ratio[3] = gage_flow[3] / NHD_reach_cumulative_drainage_area[3]
mean_flow_ratio = (flow_ratio[1] + flow_ratio[2] + flow_ratio[3] ) / reach_count
flow_estimate[subject_reach]= mean_flow_ratio * reach_cumulative_drainage_area [subject_reach]
Results:
Caveat Emptor: The CCAMP Modeling method is not currently applicable to all stream
reaches. Rivers and streams with high subsurface flows during low flow conditions and
rivers and streams located in areas without appropriate stream flow calibration gauges are
subject to unacceptable modeling error. The model appears to produce usable results for
the majority of benchmarked river and stream coastal confluences on the California
Central Coast, CCAMP staff is examining the properties of the river and stream reaches
which produce questionable results in order to automatically produce an error message
when confounding stream attributes are encountered or improve the model to address the
attributes.
The CCAMP Modeling method appears to provide enhancement of stream and river flow
estimates when compared to the NHD+ Generalized Unit Runoff Method estimates. The
method appears to provide the ability to provide enhanced temporal resolution for stream
and river flow estimations. When compared to stream transect measured flows, model
results appear to indicate that the use of NHD+ annual flow estimations and cumulative
drainage areas can effectively be used as scaling factors to hindcast daily flows in ungauged watersheds based on daily flow measurements from nearby watersheds.
Discussion:
Acknowledgments:
Appendices:
Appendix 1 – Model development process narrative with graphics
Appendix 2 – Model Benchmark Performance Evaluation with graphics
Development working notes only: Do not cite or reference.
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Appendix 1 – Narrative of development process with graphics
NHD+ Flow Estimations versus USGS Gage Measured Flows for California
2,500,000,000
NHD+ Mean Daily Flow(cubic feet per day)
y = 0.9843x + 3E+06
R2 = 0.855
2,000,000,000
1,500,000,000
1,000,000,000
500,000,000
0
500,000,000
0
1,000,000,000
1,500,000,000
2,000,000,000
2,500,000,000
USGS Gage Mean Daily Flow (cubic feet per day)
NHD+ Flow Estimations versus USGS Gage Measured Flows for California
10,000,000,000
y = 0.5923x1.0034
R2 = 0.6467
NHD+ Mean Daily Flow(cubic feet per day)
1,000,000,000
100,000,000
10,000,000
1,000,000
100,000
10,000
1,000
100
10
1
1
10
100
1,000
10,000
100,000 1,000,000 10,000,00 100,000,0 1,000,000 10,000,00
0
00
,000
0,000
USGS Gage Mean Daily Flow (cubic feet per day)
The two charts above depict several methods of visualizing the performance of the National Hydrography
Dataset Plus (NHD+) Unit Runoff Method of estimating the flows in California stream and rivers.
Development working notes only: Do not cite or reference.
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NHD+ Flow Estimations versus USGS Gage Measured Flows for
California Central Coast
12,000,000
NHD+ Mean Daily Flow(cubic feet per day)
y = 0.2598x + 623576
R2 = 0.3968
10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
0
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
USGS Gage Mean Daily Flow (cubic feet per day)
NHD+ Flow Estimations versus USGS Gage Measured Flows for
California Central Coast
100,000,000
y = 2.7485x0.8623
R2 = 0.5508
NHD+ Mean Daily Flow(cubic feet per day)
10,000,000
1,000,000
100,000
10,000
1,000
100
10
1
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000 100,000,000
USGS Gage Mean Daily Flow (cubic feet per day)
We filtered National Hydrography Dataset Plus data to examine only data from the Central Coast of
California. The two graphs above depict methods of visualizing the performance of the National
Hydrography Dataset Plus Unit Runoff Method for the Central Coast of California
Development working notes only: Do not cite or reference.
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NHD+ Flow Estimations versus USGS Gage Measured Flows for
California Central Coast
12,000,000
NHD+ Mean Daily Flow(cubic feet per day)
y = 0.2598x + 623576
R2 = 0.3968
10,000,000
8,000,000
6,000,000
4,000,000
2,000,000
0
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
USGS Gage Mean Daily Flow (cubic feet per day)
CCAMP Model Predicted Flow s versus Stream Transect Measured Flow s
California Central Coast
CCAMP Model Predicted Flow (cubic feet per day)
30,000,000
y = 1.0135x + 53.785
R2 = 0.9334
25,000,000
20,000,000
15,000,000
10,000,000
5,000,000
0
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
Stream Transect Method Measured Flow (cubic feet per day)
We constructed a model employing NHD+ Unit runoff method flow estimates as a baseline and created an
algorithm that integrated the high temporal data density of USGS gage measurements with the cumulative
drainage areas depicted in NHD+ and compared the results with the high spatial data density Stream
Transect Method measurements.
Development working notes only: Do not cite or reference.
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NHD+ Flow Estimations versus USGS Gage Measured Flows for
California Central Coast
100,000,000
y = 2.7485x0.8623
R2 = 0.5508
NHD+ Mean Daily Flow(cubic feet per day)
10,000,000
1,000,000
100,000
10,000
1,000
100
10
1
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000 100,000,000
USGS Gage Mean Daily Flow (cubic feet per day)
CCAMP Model Predicted Flow s versus Stream Transect Measured Flow s
California Central Coast
CCAMP Model Predicted Flow (cubic feet per day)
100,000,000
y = 38.966x 0.743
R2 = 0.7378
10,000,000
1,000,000
100,000
10,000
1,000
100
10
1
1
10
100
1,000
10,000
100,000
1,000,000
10,000,000
100,000,000
Stream Transect Method Measured Flow (cubic feet per day)
The reconciliation of spatial and temporal information densities employed by the model appears to be
reasonably consistent with NHD+ method findings on the central coast of California .
Development working notes only: Do not cite or reference.
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Cumulative Drainage Area
9,772
10,000
3,184
Square Kilometers
1,000
497
648
357
298
100
152
107
77
63
62
25
21
4
3
Moore Creek
Porter Gulch
10
Laguna Creek
Tembladero
Slough
Salinas River
Big Sur River
Carmel River
Carmel River
Pajaro River
Waddell Creek
Soquel Creek
San Lorenzo
River
Scott Creek
Branciforte
Creek
Aptos Creek
1
The monitoring sites employed by the Central Coast Long Term Environmental Assessment Network
(CCLEAN) provide an example of an application of the model. Stream transect method measured flows
were used as a benchmark for model performance. Model predicted flows exhibited reasonably high
correlation with stream transect measured flows. The square of the Pearson product moment correlation
coefficient was above 0.93 for the array of CCLEAN sites examined.
Development working notes only: Do not cite or reference.
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CCAMP Predicted Flow s
Predicted Flow (cubic feet per year)
12,000,000,000
10,000,000,000
8,000,000,000
6,000,000,000
4,000,000,000
2,000,000,000
Porter Gulch
Moore Creek
Laguna Creek
Tembladero
Slough
Salinas River
Big Sur River
Carmel River
Carmel River
Pajaro River
Waddell Creek
Soquel Creek
San Lorenzo
River
Scott Creek
Branciforte
Creek
Aptos Creek
0
The NHD+ Unit runoff method model uses five gauges within a 200 mile radius as a basis for predictions.
The CCAMP model uses gages located substantially closer to the sites of interest. The CCAMP model
uses one to three USGS gage measured flows in conjunction with NHD+ Unit runoff method predicted
flows. The above two charts depict the difference between the original NHD+ predicted flows and
CCAMP model predicted flows.
Development working notes only: Do not cite or reference.
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Big Sur River Mean daily flow (cubic feet per day)
14,000,000
12,179,434
12,000,000
10,715,847
10,000,000
8,000,000
7,017,848
6,000,000
4,000,000
2,237,760
2,000,000
0
NHD
USGS
STM
Model
Model Single Gage Example: The Big Sur River site has a single USGS gage and a stream transect method
monitoring site. The NHD+ unit runoff method predicted flow underestimates actual flow. This
underestimation may be due to the unit runoff method’s use of five calibration gauges within a 200 mile
radius as a basis for prediction. The western slope of the Santa Lucia Mountains has rainfall conditions
which do not extend over such a broad spatial range. The stream transect method (STM) measured flow
also underestimates flows at the site. This underestimation may be due to lack of ability to measure high
flows due to safety concerns. The model predicted flow is slightly higher than the USGS measured flow.
This difference appears to be due to the fact that the sites are not precisely co-located. The stream transecct
method site is located at a point that drains 152 square kilometers of watershed whereas the USGS gage is
located at a point that drains 121 square kilometers of watershed.
Development working notes only: Do not cite or reference.
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CCAMP Model Predicted Flow s versus Stream Transect Measured Flow s
California Central Coast
CCAMP Model Predicted Flow (cubic feet per day)
30,000,000
y = 1.0353x + 95507
R2 = 0.9611
25,000,000
20,000,000
15,000,000
10,000,000
5,000,000
0
0
5,000,000
10,000,000
15,000,000
20,000,000
25,000,000
30,000,000
Stream Transect Method Measured Flow (cubic feet per day)
The Model performed slightly better for the CCLEAN array of sites than for the overall Central Coast
Region sites.
Development working notes only: Do not cite or reference.
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ad j_ d if f er ence
3000%
2 50 0 %
2000%
150 0 %
10 0 0 %
50 0 %
0%
- 50 0 %
0
5,0 0 0 ,0 0 0
10 ,0 0 0 ,0 0 0
15,0 0 0 ,0 0 0
2 0 ,0 0 0 ,0 0 0
2 5,0 0 0 ,0 0 0
3 0 ,0 0 0 ,0 0 0
The majority of conflicts between model predicted flows and stream transect measured flows occur during
low flow conditions.
Development working notes only: Do not cite or reference.
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Appendix 2 - Benchmark Performance Examples
Fig x
Fig x
Fig x
Development working notes only: Do not cite or reference.
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Fig x
Fig x
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Fig x
Fig x
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Fig x
Fig x
Fig x
Fig x
Fig x
Development working notes only: Do not cite or reference.
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Model Development Notes
Development Revision history:
11/22/2006 – 11/26/2006
Removed low end flow clipping
Correct bad gage assignments for target sites
Correct linkages between target sites and NHD reaches
Correct linkages between transect sites and NHD reaches
Correct linkages between USGS gage sites and NHD reaches
11/27/2006
Implemented low flow handler using cumulative drainage area for < 5cfs as per NHD+
Doc
11/28/2006
Review correlations, slopes, and time series plots for all CCLEAN sites
Review distribution of differences between model output and stream transect flows.
Development working notes only: Do not cite or reference.
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