WRM web version, node type: Reservoir Node

A reservoir node is characterised by

• 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 optional time series of a target storage level which also has a priority level defined relative to the three standard release pathways;

• several Relase Pathways that include
  • spill above flood level, onnly constrained by the spillway capacity;
  • up to three 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.

  These release pathways can be defined

  • as an explicit release time series;
  • as a precentage of the volume available for release;
  • through a release rule, that defines the amount to be released as a (piecewise linear) function of storage level between dead storage and flood level;
  • demand driven by a downstream demand node (direct or after one confluence).

  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 on an hourly basis.

  The reservoir water budget considers inflow and outflow, evaporation and direct (effective) precipitation inpu;t 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 Data

  NAME	Reservoir name (short and descriptive, used e.g., in the node selectors).
  Type	TYPE of the object, only an additional description, as all individual configurations are parametrized
  Object link	optional link to a corresponding RIVER BASIN OBJECT of type reservoir.
  Description	free text describing the reservoir node, major assumptions, and meta data such as the source of data, reference year, etc.
  Aquifer	optional link to an aquifer to receive seepage, and for optional (future) more complex (bi-directional) interaction between reservoirs and groundwater
  Elevation (in masl)	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.
  Dam height (in m)	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.
  Flood level (in m)	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.
  Storage capacity (in Mm3)	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 storage (in %)	initial reservoir storage, in % of storage capacity
  Dead storage (in Mm3)	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)	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 (in km²)	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
  Effective area (in km²)	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.
  Reservoir Release (up to 3):	this defines the operating policy or release strategy for the three standard release pathways. Options in the pull-down menu are: precentage (of the available volume, constrained by priority and availability defined by the dead storage level or the optional reservoir target level) 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.
  Release Rule Parameters	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: zero release for the level corresponding to dead storage maximum (pathway specific maximum capcity) release corresponding to the flood level. Above flood level, water will be released with the maximum release rate plus spill capacity, untill the level drops below flood level again. 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
  Maximum release (in m³/s) capacity constraint 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.
  Spill capacity (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.
  Meteorological data:
  Precipitation (in mm)	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.
  Temperature (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.
  Reservoir Economics:
  Investment	annual equivalent costs, AEC derived from NPV
  Operations	operating costs, fixed (monthly) operating costs, variable (by m3/of release)
  Power head	power head (vertical distance of turbine from the reservoir reference elevation, measured as a positive distance).
  Power coefficient	power generation coefficient: W/m4
  Electricity cost	Euro/KWh produced 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.

  Reservoir Geometry:

  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:
  1. INPUT
     • inflow
     • direct rain input (effective precipitation)

  2. OUTPUT:
     • 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);

  3. LOSSES:
     • evaporation losses (depending on surface area and temperature);
     • seepage losses (may be added to the groundwater system, function of level).

     • STORAGE:
       • storage volume
       • storage level
       • surface area;
  A (very simple) release rule can be formulated with:

  Storage level	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