Hydrologic Engineering Center

Simulating Reservoir Systems

HEC-ResSim

To know the basic principles for simulating reservoir operation:

Operation goals by purpose

Reservoir system data requirements

Physical data

Operational data

Flow data

Simulation considerations

Topic Objective:

System extent?

Purposes?

Study objectives?

Data resources

Operational constraints

Evaluation criteria

Appropriate model

ReservoirSystem

Authorized Purposesfrom: “Digest of Water Resource Policy and Authorities”, (USACE, 1989)

1. Store or pass inflow?

2. Release water from storage or save?

3. Release from which reservoir?

4. Allocation of released water?

5. From what level in reservoir to make release?

Basic Operating Questionsfrom: “Economics of Water Resources Planning” by James and Lee

Flood: Reduce damages

Water Quality: Meet specified requirements (waterquality may be as important as quantity)

Irrigation: Meet seasonal diversion schedule

Navigation: Maintain channel depth with flow

Hydropower: Meet demand, use all release

Recreation: Maintain pool during season

Fishery: Pool fluctuation for habitat; flow and temperature in channel

Operational Goals

Do not endanger the dam

Do not contribute to downstream flooding

Do not unnecessarily store water in the flood pool

Evacuate flood storage as quickly as possible

Bottom line: Never make the downstream flooding worse than it would have been without the project!

Flood Damage Reduction Considerations

Conflict between flood and supply storage

Save space for future flood

Save water for future supply

Demand for water

Varies with season

Varies over the years

Deficiencies met from storage withdrawal

Different priorities among customers

Water Supply Considerations

Must be a Demand for Energy

Must economically meet demand

Role in meeting load affects analysis

Estimation of power potential

Firm vs. Secondary energy

Peaking vs. Base load

Capacity vs. Energy

Hydroelectric Considerations

Environmental Considerations

In-Stream flows Low flows and high flows important

Magnitude, timing, frequency, eco-response

Temperature management Selective withdrawal

Water quality management

Ecosystem in pool

Define study objectives

Develop data sets Physical, operational, flows

Validate data & operations Check flow continuity through the system

Compare simulation to historic data

Perform simulation with specified demands

Evaluate output & performance

Compare output with evaluation criteria

Steps for Simulation Analysis

Watershed & System Network

Reservoir physical data Pool Elevation - Storage - Area Dam and emergency spillway data Controlled outlet capacity - elevation

Diversion facilities

Computation points – Junctions

Routings between junctions

Physical Data for Reservoir Systems

Outdated Records and Information

Missing Information

Use of HEC-HMS and HEC-RAS

Introduction of Model Errors

Operation data – recorded versus actual field process

Physical Data Considerations & Limitations

Instream flow requirements

Non-damaging channel flow

Demand schedules for diversions

Drought contingency operation plan

Defined as rules for storage zones Max and min flows Specified release schedule Elevation - release schedule Rates of change Priorities among rules

Operational Rules for Reservoirs

Operation Zones

Flood storage

Conservation

Inactive

Additional Zones for

Emergency operation

Drought conditions

Other changes in operation goals

Storage Allocation for Simulation

Select appropriate time interval Short time interval (hourly) for flood simulations Longer time interval for water supply, ecosystem,…

Determine simulation duration Period-of-record for multiple-purpose, or Critical period for high and low flow events (must define initial conditions for each event)

Define flow data requirements for analysis Historic (gauged) events and time series Synthetic events – design and frequency floods Stochastic extension of flow record?

Reservoir System Flow Data

Define model locations and flow required

Obtain available historical data

Fill missing records Statistical processes

Simulation to estimate flow for ungauged locations

Develop local flows for model locations HMS rainfall-runoff model with DSS output

Headwater inflows

Incremental local flows (flow from area between model nodes)

“Map” model locations to DSS flow records

Developing Flow Data

Combine Physical, Operation, & Flow data

Set Initial conditions Reservoir pool level Reservoir release

Set Time Window for simulation

Set optional parameters

Perform simulation for Existing Conditions

To the Simulation, Finally!

Reservoir considers present state

Pool level compared to guide curve If above, release to draw down to curve

Limited by: Rate-of-change (operational or physical)

Channel capacity at outlet

Maximum release capacity

If below, release minimum flow required

Release Considerations for Existing Conditions

Look Downstream:

Downstream inflow (uncontrolled local flow)

Release hydrograph translation (routing effect)

Future releases, based on present release

Maximum non-damaging flow (channel capacity)

Priorities among operational rules

Release Considerations for Existing Conditions

Evaluate Output (performance criteria)

Downstream flow impacts (flood damage)

Storage utilization (risk of exceeding?)

Potential upstream impacts (pool backwater)

Impacts on other purposes (velocities, depths, duration, etc.)

Simulate Alternatives

Did the model reasonably simulate alternative?

If not, modify model data and repeat

Performance criteria – compare with Existing

Simulation Complete!

Emergency Spillway Adequacy - save the dam Emergency Gate Operations – Induced Surcharge

routing Downstream channel capacity in future

Floodplain development Changing channel due to regulated flow

Preserving storage capacity and utilization Development around pool (especially for stable pool) Sediment accumulation in pool

Low flow concerns Evaporation Seepage Channel losses

Model and Data Factors

Economics of Water Resources Planning,

L. D. James & R. R. Lee, McGraw-Hill, 1971

Management of Water Control Systems, EM 1110-2-3600, 1987

Digest of Water Resources Policies and Authorities,USACE, 1989, EP 1165-2-1

A Preliminary Assessment of Corps of Engineers’ Reservoirs, Their Purposes and Susceptibility to Drought,

HEC RD #33, 1990

Authorized and Operating Purposes of Corps of Engineers Reservoirs, USACE, 1992

Flood-Runoff Analysis, EM 1110-2-1417, 1994

Hydrologic Engineering Requirements for Reservoirs, EM 1110-2-1420, 1997

References: