Slide 1

Dr. David AhlfeldProfessor of Civil and Environmental Engineering

The Westfield River BasinOptimization Model Demonstration:Westfield River Basin Review

KVLCMTBORLVLWORWSHPKVL = Knightville (Flood Control)LVL = Littleville (Flood Control)BOR = Borden Brook (Drinking)CMT = Cobble Mountain (Drinking/Hydro)WOR = Woronoco (Hydro)WSHP = West Springfield Hydro Project (Hydro)= Ecological Point of InterestImprove current reservoir operations to increase efficiencyIncrease hydropower production, increase water supply reliability, decrease flood risk, etc.

Introduce ecological flows to operationsOptimization models will examine how altering operating policies can improve ecological flows while maintaining or improving current reservoir objectives

Plan for the future (Later Presentation)Short/long term forecasting and climate change

Why Optimize?Our Optimization ModelThe optimization model calculates releases on a daily time step for each reservoir.Releases are the DECISION VARIABLESStorages are calculated from the Releases:Storage at end of day = Storage at end of prior day + Inflow during the day Releases during the day Natural inflows to reservoirs are assumed known.

Model ConstraintsThe model releases are bounded byCONSTRAINTSExample Constraints:

Release Upper BoundRelease Through Turbine Turbine Capacity

Reservoir connectivityAssume Reservoir A flows to Reservoir BStorage of Reservoir B = Prev. Storage at B + Inflows to B + Outflows from A Releases from B

Reservoir Storage CapacityReservoir Storage Reservoir CapacityModel Objective FunctionExample Objective Functions for River Systems:

Maximize Income from Hydropower Generation Maximize Available water for municipal useMinimize Deviations from a target storage Minimize Deviations from an ecological flowThe optimization model selects releases to maximize or minimize a given objectiveTHE OBJECTIVE FUNCTIONTargetsCan be violatedPenalize the objective function as deviation from the target increases.

ExampleDeviation from Release Target = Actual Release Target Minimum Release

The objective function minimizes the deviation below the target ConstraintsCannot be violatedIf the model cannot be satisfy the constraints the problem is infeasible

ExampleReservoir Storage 50K acre-ft

The storage must be less than or equal to 50K acre-ft

LINGO will report an infeasible result

Targets vs. ConstraintsThe Westfield River Optimization ModelObjective Function:

Minimize deviations from target storages for KVL, LVL, and CMT.

Minimize deviations from minimum release targets for KVL and LVL.

Minimize flow over flood target point

Maximize power for CMT, WOR, and WSHPConstraints

Reservoir Connectivity (i.e. Storage at WOR = Previous Days Storage + Releases from KVL, LVL, CMT + Inflow to WOR Releases from WOR)

Reservoir capacities for all reservoirs

Turbine capacities for CMT, WOR, WSHP

Ramping and release constraints on reservoir releases produces more realistic hydrograph (limits the unrealistic release spikes)The optimization model is solved with LINGO which communicates with an Excel spreadsheet to read inputs (inflows) and output the releases and resulting storages.Minimize = Deviations from Target Storages at LVL and KVL + Deviations from Target Storages at CMT + Deviations above the Flood Check Points + Deviations below Min. Flow Targets at LVL and KVL + Income from CMT power generation + - Income from WOR power generation + - Income from WSHP power generation + Weight 1*Weight 2*Weight 3*Weight 4*Weight 5*Weight 6*Weight 7*Multiple Objectives and Trade-OffsTo prioritize an objective, increase its respective weight. Develop Trade-Off Curves: Run the model several times, each time changing the objective function weights. Now, lets examine some results and trade-offs from theWestfield RiverBegin with analysis of Cobble Mountain (CMT)

70,000 acre-ft reservoir that supplies water to Springfield.

30.6 MW generating capacity withdrawals to drinking water facility run through turbine and any water released back to the river runs through turbine.The trade-off: How much additional hydropower income can be obtained by relaxing the reservoirs target volume

Vary the weights on CMT Storage and CMT Hydropower

Cobble Mountain: Target Storage vs. Hydropower IncomeEach point on the curve represents an operating policy.For example, this point says if the operations keep the reservoir at target storage 99% of the time, the income is $1.7M per year Little increase in income for less reservoir reliabilityLets examine this pointReleases and Storages for Selected Point

Releases to RiverStoragesHow the Storage Changes Along The Trade-Off Curve

Scenario: Minimum Instream Flow Requirements for Cobble MountainThe optimization model lets us examine the trade-off between Cobble Mountain water supply and an instream flow requirementEach point on the trade-off curve represents the optimal operating policy for that minimum instream flow.Cobble Mountain Instream Flow Trade-Off

As expected, it is harder for Cobble Mountain to maintain its storage target with increasing instream flow requirementsInstead of focusing on one reservoir, now lets see how the optimization model can jointly optimize individual reservoirs for a downstream target

The optimization model will use these 5 reservoirs to hit the ecological target downstream.Downstream Ecological TargetThe 2-yr 10-day flow event: The 10 day flow event that is expected to occur every 2 years.

Average flow of 4,500 cfs for 10 daysThe Best Way Achieve This Flow EventUse the available storage in the flood control dams to store water for the target.

Only use Cobble Mountain Drinking water if necessary

To do this in the optimization model, heavily weight (or prioritize) CMT target storage over LVL and KVL. This will use the flood control storage first.Flood Control Trade-OffCMT storage remained constant at each scenario.

Drinking water supply not needed for ecological flow