Boundary Condition: Reservoir with Spillway
Note: The sample problems presented in this post can be downloaded here.
Figure 1: Conceptual Model of the Basic Reservoir Boundary Condition
The Feb 2022 release of HydroGeoSphere (Revision 2356) introduced a brand new boundary condition:
The new reservoir with spillway boundary condition is an improvement to the existing reservoir BC that provides you with much more control over the release of water from the reservoirs that you have incorporated into your HydroGeoSphere models.
Download the following example project to review an example of the reservoir with spillway BC, based on the always popular Abdul verification problem:
To properly introduce the new reservoir with spillway BC, it makes sense to first review the existing reservoir BC. The reservoir boundary condition facilitates the simulation of surface water management schedules that aim to remove water from instream flow nodes (overland flow and/or 1-D channel flow domains), store water, and release water back into stream flow. While water removal from instream flow is dependent upon water being present in the requisite domain, the storage is managed as an offline numerical reservoir, hence volumetric storage is independent of mesh discretization and topographic resolution. Reservoir storage can be characterized with the optional BC constraints/commands initial reservoir storage (initial volume of water stored in the reservoir at the beginning of the simulation), base reservoir storage (the base or ‘dead’ storage volume of the reservoir) and maximum reservoir storage (the maximum volume of water which can be stored in the reservoir). Figure 1: Illustrates the conceptual model of the basic reservoir BC, where inflow/outflow rates are predefined using a time-value table (subject to available water volumes).
Figure 2: Conceptual Model of the New Reservoir with Spillway Boundary Condition
The reservoir with spillway BC expands on the conceptual model above by introducing a surcharge reservoir storage parameter, spillway parameters that define the spillway discharge rate from the surcharge storage area, and the gate discharge table that controls discharge from the maximum storage area (this takes the place of a standard time-value table in the basic reservoir BC). Furthermore, inflow to the reservoir can now be more realistically defined using the Inflow hydrograph name command (see section 2.7.3.11 of the Reference Manual for full details on all of these commands!). Figure 2 illustrates the conceptual model of the new reservoir with spillway boundary condition:
The reservoir with spillway BC differs from the basic reservoir BC in the following key ways:
Inflow to the reservoir with spillway is controlled by an inflow hydrograph (using inflow hydrograph name). This inflow hydrograph must be defined with the command Set hydrograph nodes prior to defining the inflow hydrograph for the reservoir. We recommend that the hydrograph node set contains the node at which the reservoir is defined.
With the basic reservoir BC inflow is simply controlled by a time value table
Outflow from the reservoir with spillway is handled using both pre-defined volumes (i.e. gate discharge) and calculated fluxes (i.e. spillway discharge). Additional overflow discharge is activated if the amount of inflowing water exceeds the storage capacity of the reservoir.
With the basic reservoir BC outflow is simply controlled by a time value table
Application of the reservoir with spillway boundary condition follows the usual workflow, illustrated in the *.grok snippet below:
use domain type
channel
clear chosen nodes
Choose node number
21859
create node set
dam1
clear chosen nodes
boundary condition
type
reservoir with spillway
name
Dam_1
node set
dam1
inflow hydrograph name
hydro
initial reservoir storage
120
base reservoir storage
20
maximum reservoir storage
100
surcharge reservoir storage
200
spillway parameters
2.0
3.0 !width
! volume to elevation table
0 2.5
50 2.7
100 2.8
150 2.85
200 2.87
400 3.0
end
gate discharge table
0 0.02
end
nodal flux reduction by pressure head
0.01
0.1
end
Figure 3: Results of the Reservoir with Spillway Boundary Conditions
By applying hydrographs upstream, downstream and at the location of the reservoir itself we get a picture of the spillway operation (see the Dam_check.lay layout package for Tecplot, included in the project folder above). Figure 3 shows high initial inflow rates and increasing storage in the reservoir until t=3000 seconds when the rain flux terminates. Flow out of the reservoir is initially driven by the gate discharge table (0.02 m3/s), but quickly increases in response to increased storage in the reservoir (i.e. spillway discharge kicks in). Discharge from the reservoir reaches it’s peak at t=3000, but declines rapidly back to the rate specified in the gate discharge rate at t=4200. By t=9300 storage has dropped to the base reservoir storage of 20m3, and discharge from the reservoir drops to near 0.
The new reservoir with spillway boundary condition provides you with a flexible tool to simulate hydraulic control features in your HydroGeoSphere models! Please let the Aquanty team know if you have any questions!
Notes:
• The reservoir with spillway BC also supports the Nodal flux reduction by pressure head command, which may be used to limit inflow to the reservoir. We recommend this option in practice, to avoid removing too much water from the system, which can lead to model instability.
• The reservoir with spillway BC automatically writes timeseries info to the prefixo.reservoir spillway.bcname.dat file. This happens automatically and provides more detailed information that the typical Tecplot output command.