Simulating Hydraulic Structures in EEMS
Simulating hydraulic structures in hydrological and hydraulic calculations is crucial for ensuring the accuracy, safety, and sustainability of water resource management and infrastructure development projects. By considering the impact of structures on water flow, engineers can enhance the design of flood control measures and infrastructure to safeguard communities from flooding and other water-related hazards.
EEMS has been significantly enhanced over the years to provide powerful tools for simulating flow through hydraulic structures and their temporal operation. This blog provides an overview of various approaches based on flow control type options in the simulation of hydraulic structures. This is the first in a series of blogs, with subsequent blogs going into more detail on each approach.
In the Hydraulic Structure Boundary Conditions form, click on the Flow Control Type, and the drop-down menu will be displayed. There are various options based on rating curves or equations, as illustrated in Figure 1. The first seven options use a rating table or flow lookup table to describe the relationship between head and flow. These options are based on upstream elevation, upstream depth, elevation difference, elevation difference with flow accelerations, upstream and downstream elevations, upstream depth with low chord, or elevation difference with low chord. The remaining four options, which determine flow based on equations, are applicable in cases involving culverts, sluice gates, weirs, or orifices.
Rating Table/Flow Lookup Table
A rating table or flow lookup table is used to determine the flow rate (discharge) of water based on a particular water surface elevation, selected via the Flow Control Type menu. For example, if Flow derived from US Elev Whole Channel Rating Curve is selected, EEMS allows setting a boundary using a single rating curve to represent the river. This option works like a flow table or time series, with an adjustable flow multiplier across different cells. A downstream cell for flow return can be set in the Downstream Cell frame. If left blank, EE ignores the downstream end. Additionally, the Head Multiplier, Head Offset, and Flow Multiplier must be specified, as shown in Figure 2.
If the Elevation Difference with Flow Acceleration option is chosen, a lookup table is required, and the flow acceleration parameter is squared and multiplied by an acceleration factor when passing through an inlet as shown in Figure 3.
Using Equations to Define a Hydraulic Structure
EEMS simplifies the configuration of hydraulic structures such as culverts, weirs, sluice gates, and orifices through equations. This option is selected by clicking “Flow Control Type” in the menu within the Hydraulic Structure Boundary Conditions form, for example, by selecting Sluice Gate as shown in Figure 4. Clicking on the Edit button in the Equation option will display the Hydraulic Structure form. The structure type is chosen using the Structure Type option. EEMS employs the corresponding equations for the chosen hydraulic structure. For example, when selecting a sluice gate, parameters such as sill elevation, height, width, super-critical discharge coefficient, sub-critical discharge flow, free flow coefficient, and submerged discharge coefficient must be set. Similarly, for other hydraulic structures such as culverts, orifices, sharp-crested weirs, and broad-crested weirs, corresponding coefficients such as Upstream/Downstream Elevation and structure length must be defined.
If the Bi-Directional Flow option is checked in the Hydraulic Structure form, flow can occur in both directions, upstream to downstream and vice versa, triggered by changes in water levels.
In the Time Control option, hydraulic structures can be either controlled or uncontrolled. Controlled hydraulic structures have mechanisms that allow operators to regulate the flow of water. These mechanisms can include movable parts like gates that can be adjusted to control water levels and discharge rates like locks. Uncontrolled hydraulic structures do not have mechanisms to regulate flow. The flow through these structures is determined by the water level upstream and the physical characteristics of the structure. For uncontrolled structures, basic parameters must be provided as described above (Figure 4). However, for controlled hydraulic structures, a rule table must be identified, as shown in Figure 6.
Do you want to try these options for yourself? There are several examples of hydraulic structure models on the EEMS website. These include a Low Chord Trapezoidal Bridge, a Culvert with Tidal Signal, and a Sluice Gate Hydraulic Structure. You can run any of these in the free demo mode of EEMS. To see these features in action, head over to our YouTube page.
Please get in touch with us if you have comments or questions. For more information on EFDC+ capabilities, contact the DSI team today.
