# Module Reservoirs

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## Contents

## Overview

Module Reservoirs allows to compute reservois dynamic that change river flows and concentrations. Module Reservoirs recieves flows and concentrations from Module Drainage Network and gives flows and concentrations to the same module.

## Main Processes

The reservoirs do not have a explicit geometry and are located in a given Drainage Network node (that will interact flows and concetrations with it.

### Hydrology

The reservoirs minimum parameter is maximum volume (keyword MAX_VOLUME) and optionally minimum volume (keyword MIN_VOLUME, default is 0.0). Below minimum volume the reservoir does not discharge and above maximum volume the reservoir discharges the remainder so that volume does not get higher than maximum.

#### Inflows

The inflows are imposed by Drainage Network at the nodes where the reservoir are located.

#### Discharges

Via Module Discharges any discharge can be imposed (positive e.g. WWTP, or negative e.g. water abstraction for irigation).

#### Surface Fluxes

Surface fluxes as precipitation and evaporation are not computed yet but routines already exist for that purpose

#### Outflows

The outflows can be computed by defining several options:

**Outflow Unmanaged Reservoir**

1) If the maximum volume is the only information available, the reservoir will not discharge until complete full and thereafter will discharge the volume above maximum divided by time step.

2) There is the option to define unmanaged reservoir as a weir (by keyword IS_WEIR : 1) and the reservoir outflow is defined by the weir equation (also defined in ModuleDischarges). Then the crest elevation and width need to be defined.

**Outflow Managed Reservoirs**

1) If beside the maximum volume only an environmental flow (keyword MIN_OUTFLOW) is defined, then above minimum volume the environmental flow will be discharged until it reaches the maximum volume and thereafter will discharge the volume above maximum divided by time step.

2)
If an operation curve is given (keyword OPERATION_TYPE), on the form of:

- level - outflow - OPERATION_TYPE : 1
- level - outflow = percentage of inflow - OPERATION_TYPE : 2
- percentage of res volume - outflow - OPERATION_TYPE : 3
- percentage of res volume - outflow = percentage of inflow - OPERATION_TYPE : 4
- percentage of res volume - outflow = percentage of max outflow - OPERATION_TYPE : 5

then the curve is read and the outflow computed based on actual reservoir volume or level. The outflow can be given directly from volume or level or the curve can define a percentage of inflow, where the outflow will be a percentage of the inflow at that instant or a percentage of maximum outflow (usually at maximum volume).

The curves are given by <<beginoperation>> <<endoperation>> block where the first column is level (elevation) or percentage of reservoir volume and the second column is outflow (m3/s) or percentage of inflow or percentage of max outflow (0-1) and between defined points the model linearly interpolates.

If at any given instant the volume/level of the reservoir is below the lowest point of curves, it will impose environmental flow if available or zero. If at any given instant the volume/level of the reservoir is above the highest point of curves, it will impose the last point outflow.

**Reminder:** if level is used an accumulated volumes curve is required (volume - elevation)) through a <<beginaccvolumecurve>> <<endaccvolumecurve>> block where first column is reservoir volume and second is elevation.

3) There is also the option to impose the outflow (e.g. from measured data) where this is done via Module Discharges but the discharge needs to be negative and a keyword in discharge present (IS_OUTFLOW)

This management option will be given priority and will be used even that environmental flow or operation curves are defined.

### Water Properties

Concentrations are computed based on two available methods (keyword PROP_COMPUTE_METHOD):

- Instant Mixing - PROP_COMPUTE_METHOD : 1
- Mixing occurs at retention time - PROP_COMPUTE_METHOD : 2

The instant mixing method computes the new concentration as the mixing in all reservoir would occur in the given time step being a mass balance between the existing and the entering mass divided by total volume

The second method uses the first as the target concentration and computes the concentration difference and the reservoir retention time (inflow /reservoir volume).

If the retention time is lower than the time step then the new concentration is the target concentration defined by instant mixing method. If not, the new concentration will be the old plus a percentage of the difference. And the percentage is given by time step / retention time.

## Data File

### KEYWORDS

KEYWORD TYPE DEFAULT RESERVOIR_FILE char ... !File with reservoirs properties DISCHARGES 0/1 0 !Connect/Disconnect discharges SURFACE_FLUXES 0/1 0 !Connect/Disconnect surface fluxes BOTTOM_FLUXES 0/1 0 !Connect/Disconnect bottom fluxes PROP_COMPUTE_METHOD int 1 !1 instant mixing; 2 retention time full mixing CONTINUOUS 0/1 0 !is a continuation? INITIAL_VOLUME_DEFAULT_METHOD int 1 !1 start perentage full START_PERCENTAGE_FULL real 0.0 !read if INITIAL_VOLUME_DEFAULT_METHOD : 1. percentage of max volume at start <beginreservoir> ID int ... !Reservoir ID NAME char ... !Reservoir Name DN_NODE_ID int ... !Reservoir Locaton in Drainage Network Node ID COORDINATES real(2) ... !Reservoir Location in coordinates GRID_I int ... !Reservoir Location in grid coordinates I GRID_J int ... !Reservoir Location in grid coordinates J MIN_VOLUME real 0.0 !Minimum reservoir volume - below no outflow MAX_VOLUME real ... !Maximum reervoir volume - above outflows remainder OPERATION_TYPE int 4 !level - outflow - OPERATION_TYPE : 1 !level - outflow = percentage of inflow - OPERATION_TYPE : 2 !percentage of res volume - outflow - OPERATION_TYPE : 3 !percentage of res volume - outflow = percentage of inflow - OPERATION_TYPE : 4 !percentage of res volume - outflow = percentage of max outflow - OPERATION_TYPE : 5 <<beginoperation>> !Block to define operation curves <<endoperation>> <<beginaccvolumecurve>> !Block to define volume accumlated curves <<endaccvolumecurve>> MIN_OUTFLOW real 0.0 !Enviromental flow MAX_OUTFLOW real inf !Maximum outflow (limited by reservoir hudraulic structures and mandatory in case of OPERATION_TYPE : 5) <endreservoir>

### Sample

Reservoir.dat

RESERVOIR_FILE : ..\General Data\Digital Terrain\ReservoirsOperation.dat DISCHARGES : 0 SURFACE_FLUXES : 0 BOTTOM_FLUXES : 0 PROP_COMPUTE_METHOD : 1 !1 instant mixing; 2 retention time full mixing CONTINUOUS : 0 INITIAL_VOLUME_DEFAULT_METHOD : 1 !1 start perentage full START_PERCENTAGE_FULL : 0.0 !read if INITIAL_VOLUME_DEFAULT_METHOD : 1. percentage of max volume at start OUTPUT_TIME : 0 1800 TIME_SERIE : 1 TIME_SERIE_LOCATION : ..\General Data\TimeSeries\ReservoirsTimeSeriesLocation.dat

Reservoirs File

<beginreservoir> ID : 1 NAME : Reservoir Unmanaged DN_NODE_ID : 4 COORDINATES : 82 32 GRID_I : 2 GRID_J : 54 MAX_VOLUME : 10800.0 <endreservoir>

<beginreservoir> ID : 2 NAME : Reservoir Managed DN_NODE_ID : 4 COORDINATES : 825 325 GRID_I : 4 GRID_J : 9 !MIN_VOLUME : 0.0 MAX_VOLUME : 10800.0 OPERATION_TYPE : 4 <<beginoperation>> 0.0 0.0 0.1 0.1 0.2 0.3 0.3 0.5 0.5 0.8 0.8 1.0 1.0 1.0 <<endoperation>> <<beginaccvolumecurve>> 0 120 100 130 500 140 2000 150 1000 155 10800 157 <<endaccvolumecurve>> !MIN_OUTFLOW : 0.25 !MAX_OUTFLOW : 5.0 <endreservoir>