WRM, node type: Reservoir Node
Two types of reservoir nodes (that are also used to represent smaller weirs) are supported:
they only differ in the number of individually controlled release channels: one or two, with indivdual release strategies and some priority defined..
A reservoir node is characterised by
- A sub-type (for one or two independently controlled release channels)
- The reservoir configuration including geometry,
lower limits (dead storage) and upper limits (flood level)
for normal release strategies, immediate catchment, and loss/seepage;
- Local meteorology (temperature and precipitation), an immediate local catchment area;
- An optional time series of a target storage level which also has a priority
level defined relative to the three standard release pathways;
- One or two (type dependent) Relase Pathways that include
- Spill above flood level, onnly constrained by the spillway capacity;
- One or two standard release channels for downstream demands,
(a special type of reservoir specific demand node is the POWERHOUSE
for electricity production, that has as an aditional parameter the
head (vertical distance from the reservoir base level) defined as well
as the economics of investment, operations and power production benefits.
which can have an optional priority ranking defined.
No ranking defined treats all patways as equivalent, sharing any constraint equally
These release pathways can be defined
The model of a reservoir is very simple and aims at a useful functional
representation with only a minimum of parameters, sufficient within the
overall framework of a dynamic, basin wide water budget.
While the model operates on a daily time step,
due to the coupled, interdependent and parallel behaviour of the release pathways,
the reservoir releses are calculated with an adaptive computational time step.
- As an explicit release time series, externalyy defined;
- Through a release rule, that defines the amount to be released as a
(piecewise linear) function of storage level between dead storage(zero release) and flood level
(maximum release capacity); above flood level, the reservoir release at spill capcity (together
with the maximum startd release channels);
- Demand driven by a downstream demand node (direct or after one confluence).
The reservoir water budget considers inflow and outflow,
evaporation and direct (effective) precipitation input;
the effective rainfall applies to a reference area to include lateral inflow
from the immediate catchment.
Other than evaporative losses, reservoirs can also lose water through seepage.
Seepage is a function of the surface area and storage level,
and can be linked as input to an aquifer.
||Reservoir name (short and descriptive, used e.g., in the node selectors).
||TYPE that defines single and dual release channels
||optional link to a corresponding RIVER BASIN OBJECT of type reservoir. Data from the reservoir OBJECT can
selectively be inherited to the NODE, using a list of applicable properties that can be toggled on or off for inheritance.
||free text describing the reservoir node, major assumptions for the model scenario, and meta data
such as the source of data, reference year, etc.
||optional link to an aquifer to receive seepage, and for optional (future)
more complex (bi-directional) interaction between reservoirs and groundwater
|reference elevation, in meter above sea level; this defines the foot of the dam,
i.e., the level from which the (relative) reservoir storage level and height of
the dam are measured. If it is not specified (NULL),
all elevation data are assumed to be ABSOLUTE in masl.
This reference elevation PLUS the water level in the reservoir also define
the head for power production.
|height of the dam (top level or crest) or (theoretical) maximum reservoir level,
beyond which the dam will be topped (and damaged); a warning will be issued
if this level is ever reached, despite the spill gates being open.
Please note that volume that can go over the dam is unlimited.
reservoir water level corresponding to storage volume and the above surface area;
please note that this is designating the upper limit of the normal operational range,
above which the spill gates come into operation; has to be lower than dam height above.
|total (operational) storage capacity of the reservoir, this corresponds to the upper
water level l2 (or flood level) in the release rule,
above which the spill gates come into operation.
|initial reservoir storage, in % of storage capacity
|volume of dead storage in the reservoir (the volume that can not be released, in Mm3);
the corresponding water level is used in the release rule, where no more release is possible,
providing the second point for the interpolation of water level dependent outflow between
dead storage/level and flood level/storage capacity. Please note that
the water level and volume can still decrease due to evaporation and seepage.
|seepage coefficient, mm/m (per day) reservoir depth, applied to an
area approximated by the surface of the reservoir at the given depth.
|surface area of the full reservoir, at storage capacity or flood level ;
a more detailed specification of the reservoir geometry can be defined in
a separate geometry editor
|area (reservoir surface and immediate shore) for effective precipitation,
in km²; please note that this area must be larger or equal to the surface area.
Release (one or two):
|this defines the operating policy or
release strategy for the two standard release pathways.
Options in the pull-down menu are:
- by target (and explicit target release is specified
as a time series, which is met subject to priority availability constraints).
- by rule defines a release rule, specified as a piecewise linearly
interpolated release as a function of reservoir water level, see below.
- demand driven by a downstream demand node, directly following the reservoir
or after ONE confluence.
- a set of first order production RULE (IF ... THEN) (under development)
| Release from a reservoir can be specified by either:
- as a percentage value of the available volume between dead storage
(or target level, depending on release priorities) and flood level;
- a time series of target flow values, which will be released subject to availability
i.e., drawing the reservoir down to dead storage level;
- Release rules: as a piecewise linear function of water levels, with the fixed points:
Above flood level, water will be released with the maximum release rate plus spill capacity,
untill the level drops below flood level again.
- zero release for the level corresponding to dead storage
- maximum (pathway specific maximum capcity) release corresponding to the flood level.
- demand driven by a downstream demand node.
|Target release TS
||time series data for the target release, m3/s, followed by a multiplier and
the time series name, selected from the model TS data base
for each release
|maximum outflow capcity for a given release pathway; for rule based release, this is
the maximimflow just at or below flood level or at the storage level corresponding
to a full reservoir at storage capacity, in m3/s;
above flood level (specified above) the spillways will be used in
addition to the normal release mechanism (gates) operating in this case at their maximum flow;
release above flood level is therefore ≤ maximum release + spill_capacity, subject
to the availability of the corresponding volume. If the reservoir level gets above dam height
(inflow exceeds this combined spill/release capacity), the outflow is considered unconstrained,
but the dam might be damaged, so a special report/warning should be generated, similar to the
top level flooding report.
(in m³/s )
|capacity (flow) of the spill gates; this is usually substantially higher than
the maximum (normal) release at the flood level (level2)
corresponding to a full (storage capacity) reservoir. The volume between
(operational) storage capacity and the volume that corresponds to the height of the dam,
is usually reserved for emergency flood control, outside normal reservoir operation.
|time series of daily precipitation (in mm) showing a multiplier,
and the name of the time series selected; the time series is drawn under the data tables.
(in degree C)
|time series of daily average temperature (in deg. C), showing a multiplier and
the name of the time series selected; the time series is drawn under the data tables.
||annual equivalent costs, AEC derived from NPV
||operating costs, fixed (monthly)
operating costs, variable (by m3/of release)
||power head (vertical distance of turbine from the reservoir reference elevation,
measured as a positive distance).
||power generation coefficient: W/m4 |
Power Generation benefits: computed (hourly) as a function of reservoirs level:
BENEFIT = CE * POWER = FLOW * COEFF * (PHEAD+LEVEL)
where CE is the cost/value of electrcity per hour, PHEAD is the powerhead (elevation difference between
the depth corresponding to the dead storage level and the power house/turbines,
and COEFF a scaling coefficient.
This is defined by a TABLE of a set of triplets,
relating reservoir depth with the corresponding area and volumes:
|depth (m) ||surface area (km²)||volume (Mm³)
These values can be defined in a separate
reservoir geometry editor.
The default geometry is defined by a MINIMUM data set of TWO records:
0,0,0 (at the bottom of the reservoir, no water, no area, no volume) and
the values specified for: flood level - surface area - storage volume
define the second triplet, in between the model uses linear interpolation.
Please note that in the editors km² and Mm³
are being used (also for the effective area)
for formatting reasons.
Dynamic output time series:
A ReservoirNode can generate the following output time series:
A (very simple) release rule can be formulated with:
- direct rain input (effective precipitation)
- target release or planned release according to policy;
- actual outflow, (subject to availability constraints);
- violation or shortfall (0 > actual release - target);
- spill (0 < actual release - target);
- evaporation losses (depending on surface area and temperature);
- seepage losses (may be added to the groundwater system, function of level).
- storage volume
- storage level
- surface area;
||Release or outflow|
|DEPTH ≤ dead storage level (L0) ||zero release (storage volume ≤ dead storage)|
|dead storage level < DEPTH < flood level (FL)
||RELEASE = maximum release * (DEPTH-L0)/(FL-L0)|
|DEPTH > flood level || maximum release + spill_capacity ≤ excess volume |