Permaculture Tip of the day – NRCS Dam Construction Definitions

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We have our own language in permaculture. I mean the word permaculture was coined by a Tasmanian and an Australian wrote the first permaculture book “Permaculture One”.  If you have never been to either Australia or Tasmania, the movies and TV shows are not far off . Words combine into one another, shortened, and tonal inflections happening at interesting moments make for a rare and pretty dialect. Their primary language is a type of English that is very much native to their region and their accent is rather delightfully unrecognizable. Funny thing is, that myself being from Texas, it felt rather familiar and comfortable of sorts. If you ever found yourself around some of my family, all of what I mentioned earlier rings true.
Even though we have our own language which is very much a mix of other disciplines and Australian dialect, when we communicate with those in professions outside our bubble, it is wise to put on our multilingual hat and prep ourselves to communicate with them. Below is a list of definitions specifically from the USDA’s (United States Department of Agriculture) SCS’s (now the NRCS) department. It is wise to note that other parts of the world have similar, but different terms for the same or varying definition.
Base Flow is the sustained or fair-weather discharge which persists after storm runoff and associated quick return flow have been depleted. It is usually derived from groundwater discharge or gradual snow or ice melt over extended periods of time, but need not be continuous flow. (It can be based on annual or seasonal periods depending upon when major floods usually occur.)
Conservation Storage is water impounded for consumptive uses such as municipal, industrial and irrigation and non-consumptive uses such as recreation and fish and wildlife.
The Control Section in an open channel spillway is that section where accelerated flow passes through critical depth.
A Dam is an artificial barrier, together with any associated spillways and appurtenant works, across a watercourse or natural drainage area, which does or may impound or divert water.
Design Life is a period of time during which a dam is designed to perform its assigned functions satisfactorily.
A Dry Dam is a dam that has an ungated outlet positioned so that essentially all stored water will be drained from the reservoir by gravity. The reservoir will normally be dry.
An Earth Dam is a dam in which the principal barrier is an embankment of earth or rock fill or combination of earth and rock fill.
An Earth Spillway is an open channel spillway in earth materials without vegetation.
Economic life is the period of time during which economic benefits accrue to a dam.
Effective Height of Dam is the difference in elevation in feet between the lowest open channel emergency spillway crest and the lowest point in the original cross section on the centerline of the dam. If there is no open channel emergency spillway, the top of the dam becomes the upper limit.
The Emergency Spillway is the spillway designed to convey excess water through, over or around a dam.
The Emergency Spillway Hydrograph is the hydrograph used to establish the dimensions of the emergency spillway.
An Emergency Spillway System is a single emergency spillway or combination of emergency spillways designed to work together.
The Exit Channel of an open channel spillway is the portion downstream from the control section which conducts the flow to a point where it may be released without jeopardizing the dam.
The Freeboard Hydrograph is the hydrograph used to establish the minimum settled elevation of the top of the dam. It is also used to evaluate the structural integrity of the spillway system.
The Inlet Channel of an open channel spillway is the portion upstream from the control section.
Joint Extensibility is the amount a pipe joint can be extended from the fully engaged position without losing strength or watertightness. In case of rubbergasket joints it is measured from the center of the gasket to the point of flare of the bell ring or collar when the joint is fully closed.
Joint Gap is the longitudinal dimension between the end face of the spigot end of a pipe joint and the corresponding face of the bell end of the connecting pipe. It does not include the beveled portion designed for sealing compounds.
The Joint Use Pool is the portion of a reservoir which serves two or more purposes; for instance, conservation storage and floodwater storage.
A Primary Emergency Spillway is the spillway with the lowest crest elevation in an emergency spillway system.
The Principal Spillway is the lowest ungated spillway designed to convey water from the reservoir at predetermined release rates.
The Principal Spillway Hydrograph is the hydrograph used to determine the minimum crest elevation of the emergency spillway. It is used to establish the principal spillway capacity and determine the associated minimum floodwater retarding storage.
Quick return flow is the diminishing discharge directly associated with a specific storm that occurs after surface runoff has reached its maximum. It includes base flow, prompt subsurface discharge (commonly called interflow) and delayed surface runoff.
A Ramp Spillway is a vegetated spillway constructed over an earth dam in a manner such that the spillway is a part of the embankment.
The Retarding Pool is the portion of the reservoir allotted to the temporary impoundment of floodwater. Its upper limit is the elevation of the crest of the emergency spillway.
Retarding Storage is the volume in the retarding pool.
A Rock spillway is an open channel spillway through competent, non-erodible, natural rock materials.
The Sediment Pool is the portion of the reservoir allotted to the accumulation of submerged sediment during the design life of the dam.
The Sediment Pool Elevation is the elevation of the surface of the anticipated submerged sediment accumulation at the dam.
Sediment Storage is the reservoir capacity allocated to total sediment (submerged and aerated) accumulation during the life of the dam.
A Spillway is an open or closed channel, conduit or drop structure used to convey water from a reservoir. It may contain gates, either manually or automatically controlled, to regulate the discharge of water.
Storage is the capacity of the reservoir below the elevation of the crest of the emergency spillway.
A Vegetated Spillway is a vegetated open channel spillway in earth materials.
Visual Focal is an element in the landscape upon which the eyes automatically focus because the element’s size, form, color, or texture contrast clearly with its surroundings.
Hope this helps you on your quest to better understanding and communicating within and outside of our permaculture realms.
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