"They all went down to Am-ster--!" Building principles.
One of the earliest known written legal civil regulations, Hammurabi's Code of Laws, says among other things: "If any one be too lazy to keep his dam in proper condition, and does not so keep it; if then the dam break and all the fields be flooded, then shall he in whose dam the break occurred be sold for money, and the money shall replace the corn which he has caused to be ruined." It's interesting to note that there's no provision for replacing the dam, only to compensate those who were damaged. Clearly, even thirty-nine hundred years ago, ownership of a dam came with responsibilities to downstream neighbors--and the same holds true today. Since camp is in full swing this issue, it seemed appropriate to talk a bit about some of the more common issues associated with managing your dam.
Most lakes or ponds have some sort of structure that keeps the water from escaping. Some states regulate all such water bodies very closely, where others focus on the more elaborate or higher hazard structures. Regardless of your government's level of involvement, you should be aware that the maintenance and operation of your impoundment should be an integral part of your organization's risk management program. Understand from the outset, though, that not every impoundment has a dam. Depressions in the surface of the land that hold water might have been formed by glaciation and subsequently fed by surface runoff and springs beneath. While those features have issues of their own, the object of this month's discussion is restricted to man-made impoundments.
Tell Me About Parts of a Dam
Here is a picture, worth a thousand words or more to help in the rest of the discussion here--and to help you with the technical jargon, specific to earthen dams.
Your dam may not have all of these components, and since some of them are buried, you may not be able to tell. However, every dam should have an emergency spillway, and some sort of bottom drain to control water release and maintain the water level.
Water levels are managed by a number of mechanisms including pipes and valves (spillway riser and trashrack). Others have treated lumber boards set across the spillway (flashboards). As important as it is to keep the water in the pond or lake, it is perhaps even more important to be able to lower the water level when conditions warrant, say, when hurricane rains or spring snow melt runoff approaches. Never having lowered the water level, many dam owners don't know how, when, or how quickly the water level should be lowered. "Faster" is seldom "better." The key here is controlled rate of discharge.
For example, inside earthen dams, which are made of compacted clay soils, there is water between the soil grains, held there for the most part by the presence of the water that you can see in the lake. If the water level is lowered too quickly, the trapped water will attempt to flow out of the soil often times with enough pressure to take large chunks of the dam with it (sloughing). Often the sloughing brings other weaknesses to light, and these repairs get very expensive, very quickly. If you've ever dug a hole in the sand at the beach, you've seen the water rush in to the hole, and the sides have collapsed. This is basically the same process by which a dam could fail if the water is removed too quickly. Your dam professional can evaluate the all of the factors which affect this critical factor (drawdown rate) for your dam.
If there is a valve on the outlet pipe, it should be operated twice a year, spring and fall, to ensure that the level can be lowered if need be. If the valve is there, but there's fear that it might stick open or break, then it's worth the cost to have a professional underwater inspector examine it, checking all of the hidden components below the water surface and writing a report on their findings and recommendations. He'll be able to tell you which regulatory agencies need to be involved and how this is coordinated.
What Is an Emergency Spillway?
This is what should be providing water release before water flows over the top of the dam (overtopping). Generally speaking, it's a low wide area off to one side of the dam, with an elevation at least a foot below the dam crest. Its channel should be hardened with big rocks (rip rap), concrete, or some sort of matting that will allow the water to release without eroding away. Many camps, unaware of the spillway's function, have filled it and its channel--setting the stage for a catastrophic failure some time in the future.
It Sure Gets Hot out There on the Dam!
It's a good thing that we have some trees growing out there for some shade! Absolutely not! The ball of roots, called the root mat not only spreads as far as the most outstretched branches, but also can burrow deep into the core of the dam. Each root and fiber is seeking water, and the more water they find, the bigger and deeper they'll go. Eventually, you'll have what amounts to a tall, healthy lever sticking into your dam, with naturally weak soil structure on the water side of the mat. The combination of water seeping along the root paths and a strong wind could easily pry out a huge block of your dam when the tree topples. Save yourself the grief and expense of this repair and build a pavilion for shade instead.
Symptoms of Trouble
Avoiding the wet spot (seeps) with the tractor is a good idea, but it may also be a symptom of internal troubles. By itself, a seep doesn't necessarily mean that there's trouble. Generally speaking, if the water flowing from the seep is clear, it's acting like a pressure relief valve and may not be of immediate concern. If however, it is muddy, or if the volume increases, an internal failure could be on the horizon. There are some pretty simple repairs that may stem the movement of material from inside the dam, but these are solutions that should be implemented at the recommendation and under the supervision of your geotechnical engineer. In short, by not mowing it's nearly impossible to monitor seeps. If the dam is too steep to be mown by a tractor safely, a fleet of push mowers might be good insurance.
This All Sounds More Complicated Than I Thought
Where can I find help? The first person in your corner when you're trying to sort out what to do should be your insurance agent. In our conversations with some of the camp insurance industry leaders, it seems that dams and associated losses may be covered in a host of different ways--but the issue is extremely complex and whether a certain loss is covered depends on the details and specifics of the situation.
Let's consider the complete, sudden, and catastrophic dam failure resulting from spring runoff and hard rains. Your general liability insurance policy likely covers some amount of claims from damage done downstream by the ensuing flood. However, the cost of design, permitting, and construction for the repairs may be another story because the language of the policy may define structures in a way that would exclude earthen dams.
In addition, although there are coverages available to offset income losses from specific "covered perils," there are often exclusions that may exclude enough of the dam components as to effectively wipe out that coverage. In short, if you have a dam, and haven't had a conversation with your agent to specifically identify what is and what is not covered, your risk probably isn't managed as well as you might hope. It's worth mentioning also, that your agent should be working with you to weigh the costs and risks associated with bringing in a professional to develop a management and action plan. When you invest and work to manage your facility's risk, the insurance company will likely respond favorably and may benefit you in both peace of mind and in your wallet.
The Association of State Dam Safety Officials (www.damsafety.org) is an organization comprised of regulators, operators, and consultants whose focus is on the safe construction, operation, maintenance, and repair of all kinds of dams. At the time this was written, there was a clickable map about halfway down the home page that will take you to the contact information and home page of each state's Dam Safety page. Every one has downloadable documents and reference materials to help you develop a dam monitoring and maintenance program.
Finally, in the "where not to go for advice" category is the office of state dam regulators themselves. This isn't to demean their work or their role, however the focus of their mandate is the safety of the folks and property downstream of your dam. Although that is certainly a priority, their judgment and recommendations cannot be counted upon to be in your best interests. Ultimately, you'll need an engineer to sign, seal, and oversee construction of any modifications or repairs. The adage about getting something for nothing was never truer. You should rely only on the counsel and guidance of the professional engineer dam specialist working for your organization only.
Despite its apparent simplicity, the systems at work in your dam are extremely complex requiring knowledgeable, proactive management. When a camp dam fails, it can sound the death knell for the lake and its associated programs because of the time and costs of permitting, design, and construction. Can your organization afford to do without that part of the program--for years or perhaps permanently? Does your insurance cover the potential claims from folks downstream should your dam fail--and the cost of its replacement? If your answer to either of these is "No," or "I don't know," then it's probably time to take charge of this indispensable part of your facility and program by developing a monitoring and maintenance program as well as a relationship with an expert. It's like money in the bank!
Rick Stryker is a professional engineer with Camp Facilities Consulting, providing study, design, permitting, and construction consultation services to the camp and conference center community. Camp personnel may contact him at 570-296-2765 or by e-mail at email@example.com.
Originally published in the 2006 July/August issue of Camping Magazine.
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|Date:||Jul 1, 2006|
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