01_River-Basin-Hydrologic-Modeling-Tom-Fransen

River Basin Hydrologic Modeling
January 18, 2011
Ecological Flow Science Advisory Board
Tom Fransen
Division of Water Resources
NC Department of Environment and Natural Resources
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“Water links us to our neighbor
in a way more profound and
complex than any other.“
-John Thorson
3
Improve River Basin Modeling – SL 2010-143
(3) Model. – Each basinwide hydrologic model shall:
a. Include surface water resources within the river basin, groundwater
resources within the river basin to the extent known by the Department,
transfers into and out of the river basin that are required to be registered
under G.S. 143-215.22H, other withdrawals, ecological flow, instream flow
requirements, projections of future withdrawals, an estimate of return
flows within the river basin, inflow data, local water supply plans, and
other scientific and technical information the Department deems relevant.
b. Be designed to simulate the flows of each surface water resource within
the basin that is identified as a source of water for a withdrawal registered
under G.S. 143-215.22H in response to different variables, conditions, and
scenarios. The model shall specifically be designed to predict the places,
times, frequencies, and intervals at which any of the following may occur:
1. Yield may be inadequate to meet all needs.
2. Yield may be inadequate to meet all essential water uses.
3. Ecological flow may be adversely affected.
c. Be based solely on data that is of public record and open to public review
and comment.
(6) Approval and modification of hydrologic models.
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Water Resources Planning & Basin Modeling
Water Resources Planning
(No EMC Approval)
River Basin Modeling
(EMC Approval)
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Model Limits
This model is not a water quality model.
The outputs can be used to define boundary
conditions to a water quality model.
The model can not be used for flood studies.
The model does not simulate ground water.
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7
OASIS’ Flexibility In Simulating Reservoir Operations Is One Of
The Reasons We Selected It As Our Preferred Model.
Hydrologic River Basin Modeling Software
OASIS – A modeling program for simulating water supply systems.
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•Is there enough water to sustain expected
uses now and in the future?
•DWR does consider ecologic flows to be part
of “expected uses”.
•Where, when and for how long could we
expect to experience shortages?
Questions To Answer
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River Basin Model Basics
Water Balance Model
Inflow – Outflow = Change in Storage
Model is like a checkbook
Inflow = Salary
Outflow = Expenses
Storage = Bank Account
The complexity is developing the data
and equations to describe the 3
variables.
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What is a River Basin Hydrologic Model?
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"Unimpaired"
Historical Streamflows
Alternative Streamflows
Climate Change
Landuse Changes
Altered Baseflows
Inflows
Reservoir Operations
Permitted Minimum Flows
Drought Plans
Operation Guidelines
Current and Planned
Local Water Supply Plans
Self-Supplied Industries
Agricultural
Other Registered Withdrawers
Changes in demand
resulting from
climate change.
Water Use
Historical and Projected
Water Supply
Ecological Flows
Recreation
Power Production
Evaluation Criteria
Is there enough water to sustain
expected current and future uses?
Hydrologic Model Water Resources Plan
Inflow Dataset
Inflow dataset is based on “unimpaired”
USGS streamflow gage data.
“Impairments” are modifications of the
natural streamflow caused by reservoir
storage changes (includes surface
evaporation and precipitation) and
consumptive withdrawals (includes
withdrawals and discharges from municipal,
industrial, and/or agricultural uses).
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Unimpaired Inflow
Unimpaired Inflow =
Measured Gage Flow
+ Upstream Withdrawals (municipal, industrial, agricultural)
- Upstream Discharges (municipal, industrial)
+ Upstream Reservoir Storage ( + Increase / - Decrease)
+ Upstream Reservoir Surface Evaporation
- Upstream Reservoir Surface Precipitation
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Steps To Create Inflow Record
1.Unimpaired streamflow record.
The process was described in the previous slide.
2.Extend short records and fill in missing flows.
USGS extension of monthly streamflow records program
fillin is used.
3.Disaggregate the monthly data from fillin into daily
values.
The values are disaggregated by using the daily flows
from a nearby gage.
4.Use the unimpaired extended streamflow records to
create the local inflows for the nodes.
Upstream and drainage area adjustments.
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Inflow Record Issues
How good is good enough?
We’re not making watches.
Lack of good long-term historical data to create the
unimpaired flow record.
Lack of adequate long-term streamflow gages.
No adjustments for changes in land use.
No adjustments for changes in the surface water
ground water interactions.
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Hydrologic Stationarity
Key Assumption – The future will be
statistically indistinguishable from the
past.
Is stationarity dead?
Climate change and coping with non-
stationarity in water and ecosystem
management.
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Critical Assumptions:
Ground water/surface water relationships
are reflected in stream flows
Withdrawals will come from current intake
locations
Sellers will continue to meet buyers’ needs
Wastewater returns will continue at the
same percent of withdrawals and same
locations
Agricultural withdrawals will not change
significantly
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Critical Assumptions:
Stream flows will be within historical
ranges
Focus on normal and low-flow
conditions
Local water utilities are the best judges
of distribution system growth
Not a water quality model
Not a ground water model
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Water
Systems
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Nodes And Arcs
Nodes are locations of interest
Reservoirs
Demands
Junctions
Arcs represent flow between nodes
Stream reaches
Canals
pipelines
Groundwater seepage
Etc.
Water Demands
•Ann Ave Use / Seasonal
Patterns
Annual Average Use
Seasonal Use Patterns
Raleigh's Modeled Demands
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
MG
D
2008monthly
2030monthly
2050monthly
2008average
2030average
2050average
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How well does the model replicate
conditions?
Falls Lake 2007 water levels
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How well does the model
replicate conditions?
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Impacts to reservoir water
levels
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Water Resources Policy Act of 2009 (not ratified)
The precursor to 5 2010 Ratified Bills, including SL 2010-143
Cape Fear River Basin Example
Summary Of The Work Done In June 2009
• 4 Model Simulations
• Each simulation was daily with a record from 1/1/1930 through
12/31/2005
• 672 input values change for the 4 simulations.
• The baseline required approximately 150 simulations to
determine the yield for the 14 reservoirs.
• Develop A Water Withdrawal Decision Support System
(DSS)
• For the 4 simulations the DSS processed 79,057,632 output
data values.
• DWR staff used their best professional judgment to develop a
first cut at a simplified approach for the integrity criteria.
Slide - 25
Modeling Baseline
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Website – DSS
The Cape Fear is not over allocated. That is the WRONG conclusion.
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Lessons Learned
The basin model in combination with a
decision support system could be a
workable approach for basinwide
allocation analysis.
The current basin modeling approach
will require adjustments after the
integrity criteria are finalized.
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Need Provisions To Handle Drought Conditions
Comparison Of Flow Thresholds
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Alternative WQ Approach That Did NOT Work
Compared Modeled 7Q10 to the 7Q10 used for NPDES Permits
Permit Base 2008 2020 2050 Gage
System Permit
7Q10
cfs
7Q10
cfs
7Q10
cfs
7Q10
cfs
7Q10
cfs
7Q10
cfs
Burlington Eastside WWTP NC0023868 36.7 21.2 28.3 60.4
Permit %dif 9.3% -36.7% -15.5% 80.0%
Fayetteville - Cross Creek
WWTP NC0023957 346.2 338.8 213.9 189.3
Permit %dif -54.4% -55.4% -71.8% -75.1%
Graham WWTP NC0021211 36.7 21.2 28.3 60.4
Permit %dif 8.0% -37.4% -16.6% 77.8%
Randleman WWTP NC0025445 2.1 11.5 23.5 29.9 12.4
Permit %dif -57.4% 129.8% 369.8% 497.6%
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7Q10 Is Not Constant
The Drought of 1998–2002 in North Carolina — Precipitation and Hydrologic Conditions
Scientific Investigations Report 2005–5053
By J. Curtis Weaver
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Why The WQ Permit Approach Should
Not Be Used
The only time you should compare actual and model data is during the validation process.
The inflows are calibrated at the monthly level. The
users needs to be careful using indicators with a
time-step shorter than a month.
Modeling issues this approach highlighted.
We will need to have a local inflow at all nodes, not just the key calibration points.
The user needs to be careful about how the indicator is calculated.
•Inflows into the node vs. Outflows leaving the node.
Modeling and Ecological Flows
Issues/Concerns
Historically the models have focused
on water supply (municipal and
industrial) reliability.
Larger streams and rivers that support or
the potential to support withdrawal and
discharges of 100,000 gpd or greater.
Calibration and validation is concentrated
on normal and low flow periods, when the
water supplies are stressed.
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Modeling and Ecological Flows
Modeling Issues That Needed To Be Reviewed
Need to be sure the model scale works
for the issue being evaluated.
Roanoke River Striped Bass spawning
flowing a good fit.
Habitat needs for the Carolina heelsplitter
in Goose Creek is not a good fit.
Need to be careful if the ecological flow
requirements includes one or more
high flow statistic.
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Questions
Contact Information
Tom Fransen, Deputy Director
[e-mail]
919-715-0381
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