Introduction

The Integrated Reservoir Model is a General Adapter module written in Java, developed by Deltares. The model class is part of the Delft-FEWS code base.

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The reservoir model requires at a minimum the following timeseries:

• level or storage state value (at model start time)
• inflow timeseries (complete run period)
• release timeseries (optional)   

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The executeActivity runs the model. The model runs of the Delft-FEWS JRE, so the ReservoirModelAdapter binaries can be specified within the binDir element. The Reservoir Model class itself is called nl.deltares.fews.reservoirmodel.ReservoirModelAdapter. It is required to provide the path of the run_info file as an argument to the model.

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The model definition for the reservoir can be configured in a model file that follows the Integrated Reservoir Model schema. The model options are described below.

Schema

An example Integrated Reservoir Model file is For reference, an example IntegratedReservoirModel file is attached.

<IntegratedReservoirModel xmlns="http://www.wldelft.nl/fews" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.wldelft.nl/fews https://fewsdocs.deltares.nl/schemas/version1.0/adapter-schemas/IntegratedReservoirModel.xsd">
    	<general>
        		<missingValue>-999</missingValue>
    	</general>
    	<reservoir id="H555001">
        		<general>
      			<description>reservoir management H555001</description>
			<poolRoutingScheme>levelPoolMethod</poolRoutingScheme>
			<dynamicInterpolation>true</dynamicInterpolation>
			<interpolationMethod>linear</interpolationMethod>
			<elevationInterval>0.0005</elevationInterval>
			<extrapolationMethod>linear</extrapolationMethod>
		</general>
      <description>reservoir management H555001</description>   <!--Height (LGH) vs. Storage (m3)-->
        <storageCharacteristics>
      <poolRoutingScheme>levelPoolMethod</poolRoutingScheme>
      <storageTable>
      <dynamicInterpolation>true</dynamicInterpolation>
            <elevationInterpolationMethod>linear interpolation</elevationInterpolationMethod><elevationStorageRecord elevation="292.9" storage="0"/>
            <elevationInterval>0.00005</elevationInterval>    <elevationStorageRecord elevation="293.0" storage="500"/>
        </general>
        <!--Height (LGH) vs. Storage (m3)-->...
        <storageCharacteristics>
            <storageTable>
                 <elevationStorageRecord elevation="292335.94" storage="0720992000"/>
                <elevationStorageRecord elevation="293335.06" storage="500732795000"/>
            </storageTable>
        ...</storageCharacteristics>
        <!--Height (LGH) vs Spill (m3/s-->
        <elevationStorageRecord<uncontrolledOutlet elevationid="335.4" storage="720992000"/outlet">
            <capacityCharacteristics>
    <elevationStorageRecord elevation="335.6" storage="732795000"/>
            </storageTable><outletTable>
        </storageCharacteristics>
        <!--Height (LGH) vs Spill (m3/s--    <elevationOutletRecord elevation="292.9" outlet="0"/>
        <uncontrolledOutlet id="outlet">
                <capacityCharacteristics>
                <outletTable><elevationOutletRecord elevation="293.0" outlet="0"/>
					...
                    <elevationOutletRecord elevation="292335.94" outlet="09768"/>
                    <elevationOutletRecord elevation="293335.06" outlet="010278"/>
				</outletTable>
			...
                    <elevationOutletRecord elevation="335.4" outlet="9768"/>
                    <elevationOutletRecord elevation="335.6" outlet="10278"/>
                </outletTable>
            </capacityCharacteristics>
            <input>
                <release>QOut</release>
            </input>
            <output>
                <release>QOut</release>
            </output>
        </uncontrolledOutlet>
        <input>
            <inflow>IIn</inflow>
            <level>HIn</level>
        </input>
        <output>
            <inflow>IOut</inflow>
            <release>QOut</release>
            <storage>SOut</storage>
            <level>HOut</level>
        </output>
    </reservoir>
</IntegratedReservoirModel>

general

In the general section, a missingValue element needs to be configured. It is important to match the missingValue as defined in the Delft-FEWS General Adapter configuration for the model run.

reservoir

The reservoir element contains the following sections:

• general
• uncontrolledOutlet
• input
• output

general

The general section of the reservoir element contains the follwing fields:

• poolRoutingScheme
• dynamicInterpolation
• elevationInterpolationMethod
• elevationInterval
• storageCharacteristics

poolRoutingScheme

for the poolRoutingScheme element, one can choose the following options:

• levelPoolMethod
• backwardsEulerMethod

levelPoolMethod

The Level Pool method is a well known method for reservoir routing. in FEWS the method described in Applied hydrology from V.T.Chow is used. The level pool routing method is also referred to as Storage routing, the Storage-Indication method, or the Modified Puls method.

The reservoir routing procedure in the Level Pool method is as follows:

We define the value G is a function of Storage and Outflow, defined as G[S] = 2*S/Δt + O

where:

• S represents the reservoir storage
• O represents the reservoir release
• Δt represents the time step

For each row in the the uncontrolledOutlet capacityCharacteristics outletTable, we can now precompute a G[S] value. This allows us to look up the release O for a given G.

The level pool method makes use of the following relations, that follow from the water balance equations (details in the handbooks):

K[t] = G[t-1] - 2*O[t-1]

G[t]= ( I[t-1] + I[t] )+K[t]

For the computation, we loop over all time intervals from t=1 to t=t_end.

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1. Use the state values as provided in the input files. If either a level, or a storage are provided, look up the equivalent value.
2. In case both level and storage are provided, use the lookup value to determine any inconsistencies. If found, the level is used as the basis and the storage at t=0 is recalculated
3. no computation takes place at t=0

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</capacityCharacteristics>
		</uncontrolledOutlet>
		<input>
			<inflow>IIn</inflow>
			<level>HIn</level>
			<release>QOut</release>
		</input>
		<output>
			<inflow>IOut</inflow>
			<release>QOut</release>
			<storage>SOut</storage>
			<level>HOut</level>
			<error>EOut</error>
		</output>
	</reservoir>
</IntegratedReservoirModel>

In XML Grid View this looks the following

Image Added

general

In the general section of the reservoir model, a missingValue element needs to be configured. It is important to match the missingValue as defined in the Delft-FEWS General Adapter configuration for the model run.

reservoir

The reservoir element contains the following sections:

• general
• uncontrolledOutlet
• input
• output

general

The general section of the reservoir element contains the follwing fields:

• poolRoutingScheme
• dynamicInterpolation
• interpolationMethod
• elevationInterval
• extrapolationMethod (from 2023.02)
• storageCharacteristics

poolRoutingScheme

for the poolRoutingScheme element, one can choose the following options:

• levelPoolMethod
• backwardsEulerMethod

levelPoolMethod

The Level Pool method is a well known method for reservoir routing. Level Pool routing is a procedure for calculating the outflow hydrograph form a reservoir with a horizontal water surface, given its inflow hydrograph and storage-release characteristics. The level pool routing method is sometimes also referred to as Storage routing, the Storage-Indication method, or the Modified Puls method. For this reservoir model, the method described in Applied Hydrology from V.T.Chow (1988) is used.  

The reservoir routing procedure in the Level Pool method is as follows:

We define the value G is a function of Storage and Outflow, defined as G[S] = 2*S/Δt + O

where:

• S represents the reservoir storage
• O represents the reservoir release
• Δt represents the time step

For each row in the the uncontrolledOutlet capacityCharacteristics outletTable, we can now precompute a G[S] value. This allows the model to look up the release O for a given G.

Image Added

The level pool method makes use of the following relations, that follow from the water balance equations (details in the handbook):

K[t] = G[t-1] - 2*O[t-1]

G[t]= ( I[t-1] + I[t] )+K[t]

 For the computation, we loop over all time intervals from t=0 to t=t_end.

1. If t=0
   1. Use the state values as provided in the input files. If either a level, or a storage are provided, look up the equivalent value.
   2. In case both level and storage are provided, use the lookup value to determine any inconsistencies. If found, the level is used as the basis and the storage at t=0 is recalculated
   3. no computation takes place at t=0
2. If t=1 then
   1. K[1] = 2*S[0]/Δt - O[0] (inital storage and release values are known)
   2. G[1] is computed with G[1]= ( I[0] + I[1] )+K[1]
   3. Compute outlet O[1] by linearly interpolating the precomputed table using O(S) and G(S).
   4. In case an outlet O_input[1] timeseries is provided as part of the inputs, set O[1] = O_input[1]
   5. Compute storage S[1] = S[0] + Δt* ( I[1] - O[1] )
3. If t>1 then
   1. K[t] = G[t-1] - 2*O[t-1]
   2. G[t] is computed with G[t]= ( I[t-1] + I[t] )+K[t]
   3. Compute outlet O[t] by linearly interpolating the precomputed table using O(S) and G(S).
   4. In case an outlet O_input[t] timeseries is provided as part of the inputs, set O[t] = O_input[t]
   5. Compute storage S[t] = S[t-1] + Δt* ( I[t] - O[t] )

A model that is configured to use the level-pool method will write the values for G and K for each timestep in the the diagnostics when run in debug mode.

backwardEulerMethod

The Backward Euler reservoir routing scheme is an implicit scheme that uses the backward difference approximation for the derivative. The equation for the backward Euler reservoir routing scheme can be written as follows:

S[t+1] = S[t] + Δt* ( I[t+1] - O[t+1,S[t]] )

where:

• S[t+1] represents the reservoir storage at the next time step (n+1)
• S[t] represents the reservoir storage at the current time step (n).
• Δt represents the time step.
• I[t+1] is the inflow into the reservoir at the next time step (n+1).
• O[ t+1, S[t] ] is the reservoir release at the next time step (n+1), based on the storage-release relation using S[t] for the lookup input.

dynamicInterpolation

When the dynamicInterpolation element is set to true, the level/storage and level/outlet tables are inteprolated dynamically (every timestep), to the precise value, using the elevationInterpolationMethod. In this case, the elevationInterval element is ignored. 

When the dynamicInterpolation element is set to false, the level/storage and level/outlet tables are precalculated (only once) using the elevationInterpolationMethod, to the specified elevationInterval.  

interpolationMethod

Linear interpolation is the only available interpolation method

elevationInterval

The elevationInterval is the elevation resolution at which the configured level/storage and level/outlet tables need to be recalculated to achieve a higher granularity. Note that the level output at each timestep is processed to that specific elevationInterval. When the model looks up a value from the table, the largest precalculated table elements smaller than the lookup value will be used (i.e. the model always rounds down). The consequence is that reservoir inflows/releases at a timestep that result in level/storage changes smaller than the interval/resolution will not be taken into account. The model does not perform any shadow accounting to keep track of these volumes. This means that the model will generally underestimate the flow when dynamicInterpolation element is set to false, and water balance will not be closed for that run type. For larger reservoirs (more volume per unit water disk) the elevationInterval needs to be set to higher resolutions to account for this. 

extrapolationMethod

The available extrapolation options are: notAllowed. linear, maxMin

storageCharacteristics

The storageCharacteristic storageTable contains a storage-level lookup table that is strictly increasing. Note that this table should have the identical storage inputs as the capacityCharacteristics outletTable from the uncontrolledOutlet.

uncontrolledOutlet

The uncontrolledOutlet element contains capacityCharacteristics outletTable which relates storage-release. Note that this table should have the identical storage inputs as the storageCharacteristic storageTable.

input / output variables and files

In the input section, the model input variables will be configured.

The <input><inflow> element is required

The <input><level> element is optional, and can be set to the timeseries variable that can overwrite (take precedence) over the level as a result from the release table computation. For a given timestep, if the level input timeseries (e.g. HIn) contains a value, this level is applied. The model will determine the resulting release from closing the waterbalance (thus not using the release lookup value)

The <input><release> element is optional, and can similarly be set to the timeseries variable that can overwrite (take precedence) over the lookup value for the outlet. This means that for a given timestep, if the outlet input timeseries (e.g. QIn) contains a value, this release is applied. This input option was added in 2023.02

When both a level and a release input value are available for a timestep, the model will use those values and write them to the output. A waterbalance error term will be calculated and saved for that timestep as well.

The model will look for the required variables in the parameter field of the PI timeseries (see idMapping). The Reservoir Model code will try to parse the configured model variables (like IIn, QOut, etc) from the parameterId of the PI timeseries, the locationId is not used. In the output section, the model output variables will be configured. When writing the output timeseries, the locationId used in the import PI xml files will be used as the locationId in the output PI xml files. The output model variableId's will be used as the parameter in the timeseries.

The naming convention of the input and output timeseries filenames are free, the model will determine which files to read for the input based on the inputTimeSeriesFile filed in the run_info file. The following two input timeseries files are suggested:

• importState.xml
  • level values, or (HIn)
  • storage values (SIn)
• import.xml
  • inflow (IIn)
  • outlet (optional) (QIn)

The following output timeseries file is suggested:

• export.xml
  • inflow (IOut)
  • release (QOut)
  • storage (SOut)
  • level (HOut)
  • error (EOut)

Note that for the suggested variableId's in the provided example, the postfix In and Out are used to denote if the series are Inputs for, or Outputs from the model.

State values

The startDateTime and endDateTime in the run_info file are used by the model to determine the start (startDateTime) and end (endDateTime) of the model run. The model will pick the starting (state) value for level/storage (level has precedent in case of an inconsistency), inflow, outlet from the inputTimeSeriesFiles at the specific datetime. It will use the output variables to look for the state timeseries. The model will first check for a state level value. If a starting level value is missing in the input, the model will use the starting storage value. If both starting level/storage cannot be determined from the input files, the model will use the first level element as defined in the storage table as the starting level. A Warning message will be generated to notify the operator of this situation.

Inflow and outlet values at the starting time are not required at the first timestep and these values will not be used for storage calculations (no calculation at the first timestep). When these values are not provided as inputs, a value of 0 is assumed (and written to the output).

When no inflows into the reservoir are defined at all, the model will not calculate, but also it will not error out. It will produce and export.xml with missings (except for the initial values). When some intermediate inflow values are missing, the model will stop calculating at the point. It will not error out (and not throw a warning), it will produces an export.xml with calculated values up until the point an inflow value was missing and it will have missings for all outputs from that moment in time.

In case state functionality is configured in the 

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backwardEulerMethod

The backward Euler reservoir routing scheme is an implicit scheme that uses the backward difference approximation for the derivative. The equation for the backward Euler reservoir routing scheme can be written as follows:

S[t+1] = S[t] + Δt* ( I[t+1] - O[t+1,S[t]] )

where:

S[t+1] represents the reservoir storage at the next time step (n+1)

S[t] represents the reservoir storage at the current time step (n).

Δt represents the time step.
I[t+1] is the inflow into the reservoir at the next time step (n+1).
O[t+1,S[t]] is the reservoir release at the next time step (n+1), based on the storage-release relation using S[t] for the lookup input.

dynamicInterpolation

When the dynamicInterpolation element is set to true, the level/storage and level/outlet tables are dynamically (every timestep) interpolated to the precise value, using the elevationInterpolationMethod. In this case, the elevationInterval element is ignored. 

When the dynamicInterpolation element is set to false, the level/storage and level/outlet tables are precalculated (only once) using the elevationInterpolationMethod, to the specified elevationInterval.  

elevationInterpolationMethod

Linear interpolation is the only available interpolation method

elevationInterval

The elevationInterval or elevation resolution at which the configured level/storage and level/outlet tables need to be recalculated. Note that the level output at each timestep is processed to that elevationInterval. When a value needs to be determined from the table the largest entry that is still smaller than the precalculated table elements is used (the model always rounds down). The consequence is that reservoir inflows/releases at a timestep that result in level/storage changes that are smaller than the interval/resolution will not be taken into account. This means that the model will underestimate the flow and water balance will not be closed.  

storageCharacteristics

The storageCharacteristic storageTable contains a storage-level lookup table that is strictly increasing. Note that this table should have the identical storage inputs as the capacityCharacteristics outletTable from the uncontrolledOutlet.

uncontrolledOutlet

The uncontrolledOutlet element contains capacityCharacteristics outletTable which relates storage-release. Note that this table should have the identical storage inputs as the storageCharacteristic storageTable.

The <input><release> element can be set to the timeseries variable that can overwrite (take precedence) the lookup value for the release. 

The <output><release> element determines where the resulting release timeseries is saved to 

input / output variables and files

In the input section, the model input variables will be configured. The model will look for the required variables in the parameter field of the PI timeseries (see idMapping). The Reservoir Model code will try to parse the configured model variables (like IIn, QOut, etc) from the parameterId of the PI timeseries, the locationId is not used.

n the output section, the model output variables will be configured. When writing the output timeseries, the locationId used in the import PI xml files will be used as the locationId in the output PI xml files. 

The naming convention of the input and output timeseries filenames are free, the model will determine which files to read for the input based on the inputTimeSeriesFile filed in the run_info file. The following two input timeseries files are suggested:

• importState.xml
  • level values, or (HIn)
  • storage values (SIn)
• import.xml
  • inflow (IIn)
  • release (optional) (QIn)

Note that for the suggested variableId's, the postfix In and Out are used to denote if the series are Inputs for, or Outputs from the model.

The startDateTime and endDateTime in the run_info file are used by the model to determine the start (startDateTime) and end (endDateTime) of the model run. The model will pick the starting (state) value for level/storage (level has precedent in case of an inconsistency), inflow, release from the inputTimeSeriesFiles at the specific . If a starting level value is missing, the model will use the starting storage value. If both starting level/storage cannot be determined from the input files, the model will throw an error. Inflow and release values at the starting time are not required at the first timestep. When they are not found, a value of 0 is used.

The following output timeseries file is suggested:

• export.xml
  • inflow (IOut)
  • release (QOut)
  • storage (SOut)
  • level (HOut)

In case state functionality is configured in the run_info file (inputStateDescriptionFile is defined), the model will also write (all) the outputs to the write location as defined in the stateLocation file (e.g. exportState.xml)

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Reservoir Model specifics

• The model Integrated Reservoir Model can be considered "timestep ending", similar the the timestep definition of Delft-FEWS.
• No calculations/processing is performed at the first timestep (t=0, startDateTime as set in the run_info.xml file)

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The Reservoir Model can be run in parallel from Delft-FEWS. The runInLoop element of the workflow should be set to false. The general section of the General Adapter configuration should contain the %TEMP_DIR% property as the model rootDir. And lastly, to enable the parallel running of ensemble members the runInLoopParallelProcessorCount entry must be set in the global properties file. Here you either specify the number of cores to use or specify 100 to use all available cores.In the workflow

The workflow definition for a parallel model run:

    <activity>
        <runIndependent>true</runIndependent>
        <workflowId>Reservoir_Forecast</workflowId>
        <ensemble>
            <ensembleId>ENSEMBLE</ensembleId>
            <runInLoop>false</runInLoop>
        </ensemble>
    </activity>

The general section of the General Adapter configuration:

<general>
  <rootDir>%TEMP_DIR%</rootDir>
  <workDir>%ROOT_DIR%/work</workDir>
  ...
</general>

In Entry in the global properties:

# to use 4 cores/cpu's:
runInLoopParallelProcessorCount=4

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From Delft-FEWS version 2023.01 onwards, it will be porssible to run the Reservoir Model adapter "in-memory" from Delft-FEWS, using the inMemoryFileTransfer element of the general section set to True.  In that case, all exported and imported files are transferred in memory between Delft-FEWS and the executed Reservoir Model.