Project

UI Home

Contact UI

CE 115

Project

The "Drowning Machine"

Low head dams, those generally less than 15 feet high, have been designed by civil engineers to provide stable pools of water for irrigation, power, and other diversions from the natural stream channel. Unfortunately, the re-circulating currents at the base of these dams can easily trap swimmers and boaters, and thus frequently are called "drowning machines." There are many such dams across the nation, and civil engineers now are called upon to re-design them in a manner that serves their original purpose but makes them safer. In this project, you will re-design a model low head dam, and test it in the Department of Civil Engineering hydraulics laboratory.

Figure 1. Low head dam picture from http://www.fremontrescue.org/low-head_dams.htm. Note the inner tube!

Low head dams create what is called a submerged hydraulic jump. A hydraulic jump occurs any time flowing water changes from the supercritical state to the subcritical state. Supercritical flow generally occurs on steep slopes (such as the dam face) and disturbances on the water surface will not cause waves to travel upstream. Subcritical flow generally occurs on mild slopes, and surface disturbances will cause waves to travel upstream. Hydraulic jumps dissipate energy, through turbulence, when flow is forced from supercritical to subcritical by, for example, a change in the channel bottom slope; they are submerged when the downstream water covers the jump itself. We'll discuss some details about hydraulic jumps in class (and you will learn much more in later classes!).

As shown in Figure 2, the submerged hydraulic jumps caused by low head dams can trap boaters and swimmers because the water at the surface actually travels upstream for some distance below the dam. The boil line divides the upstream and downstream moving flows at the surface (also look at Figure 1). Since boats and swimmers wearing PFDs (life jackets) are buoyant, they get trapped between the dam face and the boil line. If you ever get stuck in one of these, your best bet might be to dive to the bottom, following the water that comes directly down the dam face and out the back of the hydraulic.

Figure 2. Swimmer caught downstream of a low head dam, from http://www.fremontrescue.org/low-head_dams.htm.

Not all hydraulic jumps are dangerous. In fact, kayakers surf some of them (in particular, those that are not submerged), as shown in Figure 3. In addition to mitigating a hazard, some low head dams can be redesigned to create whitewater play spots which have economic benefits to communities beyond the original purpose of the dam.

Figure 3. Kayaker spinning on a wave in Green River, Wyoming (http://playak.com/article.php?sid=1105). This wave is in a whitewater park, designed for kayakers. The water is moving from right to left in this photo - the "foam pile" behind the kayaker is the turbulence, in the form of a weak, not submerged hydraulic jump, that dissipates energy in transition from supercritical (right, in the wave trough) to subcritical (left, out of photo).

Here are some YouTube videos of whitewater play spots:

Salida Park, Colorado

Buena Vista, Colorado

Bladder Wave, Idaho

In this class, you will re-design a model low head dam for the primary purpose of mitigating the danger to swimmers and boaters, and for the secondary purpose of providing a spot for kayakers to play. You will build a re-designed model dam, and test it at various flow rates in a design competition to be held in a flume in the hydraulics laboratory. Flume dimensions and flow rates will be provided subsequently. As one design goal, the water level upstream of the dam must not change in the re-design. In the competition, model boaters and swimmers will be floated through the dam and into the "play spot" you create (see this video for what model boaters can do!). Points will be awarded for how well your design performs with respect to upstream water level, danger mitigation, potential for the new dam to create a feature attractive to whitewater boaters, and economics (estimated cost of construction). More details will be provided as the semester progresses.

Design Process

This project is like many design projects you will encounter, in that it requires that certain steps be taken to successfully complete the project. Here are the steps (Hyman, 1998):

	Recognize the need. In this case, you need to complete the design project, as defined, to pass the class. In Civil Engineering practice, the need is typically based on serving the public needs in some manner (need to build a road, need to treat the water, need to construct a hospital, etc.). This step is where the purpose is established.
	Define the problem. Clearly identify the goals, objectives, and constraints.
	Plan the project. Break the project down into manageable tasks, and establish starting and ending dates for each task. Note that in order to start a particular task, it may be necessary to first complete a different task!
	Gather information. There is usually information available from similar projects, but each design situation is unique.
	Develop design alternatives. Based on the goals, objectives, and constraints, a range of design alternatives are conceptualized.
	Evaluate alternatives. Each alternative must be evaluated with respect to the goals, objectives, and constraints. Also, economic considerations are critically important at this stage of design.
	Select the best alternative. Based on calculations made in the previous step combined with engineering judgment, the best alternative is selected.
	Communicate the design. Civil Engineers must communicate the results of their work clearly to clients, colleagues, government and regulatory agencies, and the public. Effective oral and written communication skills are essential.
	Implement. In this step, the preferred alternative is executed, tested, analyzed, and modified if necessary. The "as-built" performance is compared to the predicted/modeled performance.

Project Evaluation

Each team's project will be evaluated based on the following criteria:

	Competition results (20%)
	Aesthetics and creativity (20%)
	Written project report (40%)
	Oral project presentation (20%)

The written report will be evaluated for technical correctness, quality of writing, quality of presentation (formatting, graphics, etc.), and completeness. It shall contain the following components (this list is not inclusive of what you are to submit - for example, you should have a letter of submittal):

	Introduction. Includes the problem statement and objectives. This is background information necessary for the reader to understand the rest of the report.
	Design. Discuss design alternatives, performance predictions, calculation summaries, limitations, and constraints.
	Construction details. Can someone else build your design given the information you provide in this section? This include materials (simple!) and dimensions.
	Results. How did it work? Include calculation summaries and quantitative results.
	Conclusions. Based on the results, describe what could be done to make the design better. Also discuss how the performance could have been better predicted.
	Appendixes. For this report, there should be at least three: your approved/signed initial design, detailed calculations, and the draft report. You may see the need for others as well.

Schedule

Please see the Schedule page.