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Reservoirs are used to store an inflow and, depending on the current storage content and operating rules, to release water for different uses to up to three different system elements. With the possibility to regulate and control releases, it is an extremely flexible system element with a variety of options. Originally, the reservoir was developed to represent reservoirs behind dams, but it can also be used to model other reservoirs such as flood control reservoirs or similar. Additionally, it is possible to optionally simulate the addition of water to the reservoir by precipitation, as well as losses from the reservoir by evaporation and infiltration.

The reservoir system element can also be used to simulate hydro power plants.

Rating Curve

The reservoir rating curve defines the relationship between storage volume, water level and surface area. It forms the basis for all calculation options that depend on not only the storage volume but also the water level and/or the surface area e.g., precipitation/losses, flow over a weir, pressurized flow through pipes.

Releases

The term release is used to describe any discharge of water according to operating rules from the reservoir to the downstream area through regulated or unregulated outlets. This includes controlled releases through operating and bottom outlets as well as releases via a spillway.

Releases are often related to operating rules, therefore, it is possible or sometimes also necessary to define several releases for each outlet.

Calculation Options

Independent of the selected calculation option, releases can always be scaled with a system state/control cluster, which makes it possible to model complex operating rules, which are not only dependent on states within the reservoir, but also on other states within the river basin.

Release per Timestep / Release Sequence

With this option, you define the release values by directly entering (up to 365) values. During the simulation, these values are then used as release values for the individual simulation timesteps in the given order.

Function (+ Graph/Time series)

The outputs are defined as content-dependent functions through the input of grid points. These outputs can additionally be scaled with a factor, a yearly, weekly and daily cycle (and, as with all calculation options, with a system state or a state group) or with a factor and a time series.

The following options are available as function types:

KNL	Kennlinie
LAM	Lamellenplan
XYZ	Zeitabhängige Funktion

Characteristic curve

For the characteristic curve, a time-independent content delivery function is entered. The interpolation points can be interpreted as steps or interpolated linearly.

Lamellenplan

With the option Lamella plan the storage content is divided into different areas (lamellas) over the year and these lamellas are each assigned a fixed delivery level. Thus, any ascending delivery levels are defined and for each fixed period of time the respective storage contents are entered for each of these delivery levels.

The supporting points of the lamella plan can be interpreted as block steps. However, it is also possible to interpolate linearly in time and/or to interpolate linearly between the grid points of the contents/output values.

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  Comparison of a lamella plan in the two- and three-dimensional representation,
  Interpretation: constant Block

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  Comparison of a lamella plan in the two- and three-dimensional representation,
  Interpretation: linearly interpolated (in time and between content/distribution support points)

Time dependent function

The time dependent function is very similar to the slat plan, but a bit more flexible: The support points for the output values must be the same for the different time periods only in number, but not in value, and they do not necessarily have to be ascending. So you can define arbitrary functions with their respective content and output values for different time periods.

By default the entered interpolation points are interpreted as block steps. However, it is also possible to interpolate linearly in time and/or to interpolate linearly between the grid points of the contents/output values.

Weir raid

The charge is calculated by the weir formula according to Poleni as a perfect / imperfect raid.

Pressure pipeline

The fee is calculated using the Prandtl-Colebrook and Darcy-Weisbach rates.

Turbine

Based on the characteristics of the turbine, the turbine flow is determined depending on the storage tank content and the underwater level, so that the desired performance is maintained as long as the maximum possible flow rate of the outlet is not exceeded. See also the page on hydropower plants.

Boundaries

The physically maximum possible output can also be entered for the individual outlet organs of the storage tank as a function of the storage tank content, which additionally limits the desired outputs. A minimum permissible discharge can also be entered here, below which the discharge is set to 0.

Internal dependencies

Internal dependencies are used to define the priorities in case of several, competing deliveries from one storage. One or more charges can be reduced if another charge exceeds a certain amount or if the memory content falls below a certain amount.

The respective limits of output and storage volume for internal dependencies are constants, which can still be scaled by constant graphs.

If several charges are reduced, the order in which they are to be reduced must also be specified.

Example: If output B > 0 and the memory content S < X, then reduce output A by the amount of output B, whereby output A may not become less than zero.

This means, that between A and B a linear dependence exists as long as B is equal to the value of A. If B rises further, A remains constant zero.

Contribution/Loss at the Reservoir

A contribution or loss at the reservoir in the form of precipitation, evaporation or infiltration can be considered via two options:

• Constant chart (daily, weekly and/or yearly)
• Time series

These can be scaled by a factor. The reservoir loss/contribution is additionally scaled automatically with the current storage surface