Storage
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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 (+ Hydrograph/Time Series)
With this option, releases are defined as functions of storage volume by entering the nodes of the function. These releases can additionally be scaled with a factor, an annual, weekly and/or daily pattern (and, as with all calculation options, with a system state or a control cluster) or with a factor and a time series.
The following function types are available:
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KNL |
Kennlinie |
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LAM |
Lamellenplan |
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XYZ |
Zeitabhängige Funktion |
Rating Curve
The rating curve consists of a time-independent functional relationship between releases and storage volume. You can specify whether the function should be interpolated linearly between the entered nodes or whether the function should be interpreted as a step function.
Pool-Based Operating Plan
With the option pool-based operating plan, the reservoir storage is divided into different pools which vary over the year and these pools are each assigned a fixed release amount. A pool-based operating plan is defined by entering a number of releases with ascending amounts and specifying the corresponding storage volume for each release amount at different times of the year.
The areas between the entered nodes can be interpreted as steps. However, it is also possible to interpolate linearly in time and/or between the release amounts.
Comparison of a pool-based operating plan in the two- and three-dimensional representation,
Interpretation: constant block (steps)
Comparison of a pool-based operating plan in the two- and three-dimensional representation,
Interpretation: linearly interpolated (both in time and between pools)
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