Harry Wright Lake Reservoir EarthCache
Hidden : 9/22/2013
Difficulty:
1.5 out of 5
Terrain:
1 out of 5

Size: Size: other (other)

Join now to view geocache location details. It's free!

Watch

How Geocaching Works
Looking for a different adventure?

Please note Use of geocaching.com services is subject to the terms and conditions in our disclaimer.

Geocache Description:

This is number 15 of 18 of the Lake Road Walking/Bike Trail Series of Caches


A reservoir is a natural or artificial lake, storage pond or impoundment from a dam which is used to store water. Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.
The term reservoir may also be used to describe naturally occurring underground reservoirs such as those beneath an oil or water well.

Types

Valley Dammed Reservoir
 A dam constructed in a valley relies on the natural topography to provide most of the basin of the reservoir. Dams are typically located at a narrow part of a valley downstream of a natural basin. The valley sides act as natural walls with the dam located at the narrowest practical point to provide strength and the lowest practical cost of construction. In many reservoir construction projects people have to be moved and re-housed, historical artifacts moved or rare environments relocated. Construction of a reservoir in a valley will usually necessitate the diversion of the river during part of the build often through a temporary tunnel or by-pass channel. In hilly regions reservoirs are often constructed by enlarging existing lakes. Sometimes in such reservoirs the new top water level exceeds the watershed height on one or more of the feeder streams such as at Llyn Clywedog in Mid Wales. In such cases additional side dams are required to contain the reservoir. Where the topography is poorly suited to a single large reservoir, a number of smaller reservoirs may be constructed in a chain such as in the River Taff valley where the three reservoirs Llwyn-on Reservoir, Cantref Reservoir and Beacons Reservoir form a chain up the valley.
Bank-side reservoir
Where water is taken from a river of variable quality or quantity, bank-side reservoirs may be constructed to store the water pumped or siphoned from the river. Such reservoirs are usually built partly by excavation and partly by the construction of a complete encircling bund or embankment which may exceed 6 km in circumference. Both the floor of the reservoir and the bund must have an impermeable lining or core, initially these were often made of puddled clay, but have generally been superseded by the modern use of rolled clay. The water stored in such reservoirs may have a residence time of several months during which time normal biological processes are able to substantially reduce many contaminants and almost eliminate any turbidity. The use of bank-side reservoirs also allows a water abstraction to be closed down for extended period at times when the river is unacceptably polluted or when flow conditions are very low due to drought. The London water supply system is one example of the use of bank-side storage for all the water taken from the River Thames and River Lee with many large reservoirs such as Queen Mary Reservoir visible along the approach to London Heathrow Airport.
Service reservoir
Service reservoirs store fully treated potable water close to the point of distribution. Many service reservoirs are constructed as water towers, often as elevated structures on concrete pillars where the landscape is relatively flat. Other service reservoirs are entirely underground, especially in more hilly or mountainous country. In the United Kingdom, Thames Water has many underground reservoirs built in the 1800s, most of which are lined with brick. A good example is the Honor Oak Reservoir, constructed between 1901 and 1909. When it was completed it was the largest brick built underground reservoir in the world and is still one of the largest in Europe. The reservoir now forms part of the Southern extension of the Thames Water Ring Main. The top of the reservoir has been grassed over and is now the Aquarias Golf Club. Service reservoirs perform several functions including ensuring sufficient head of water in the water distribution system and providing hydraulic capacitance in the system to even out peak demand from consumers enabling the treatment plant to run at optimum efficiency. Large service reservoirs can also be managed to so that energy costs in pumping are reduced by concentrating refilling activity at times of day when power costs are low.

Uses

Direct water supply
Many dammed river reservoirs and most bank-side reservoirs are used to provide the raw water feed to a water treatment plant which delivers drinking water through water mains. The reservoir does not simply hold water until it is needed; it can also be the first part of the water treatment process. The time the water is held for before it is released is known as the retention time. This is a design feature that allows particles and silts to settle out, as well as time for natural biological treatment using algae, bacteria and zooplankton that naturally live within the water. However natural limnological processes in temperate climate lakes produces temperature stratification in the water body which tends to partition some elements such as manganese and phosphorus into deep, cold anoxic water during the summer months. In the autumn and winter the lake becomes fully mixed again. During drought conditions, it is sometimes necessary to draw down the cold bottom water and the elevated levels of manganese in particular can cause problems in water treatment plants.
Hydroelectricity
A reservoir generating hydroelectricity includes turbines connected to the retained water body by large-diameter pipes. These generating sets may be at the base of the dam or some distance away. Some reservoirs generating hydroelectricity use pumped re-charge in which a high-level reservoir is filled with water using high-performance electric pumps at times when electricity demand is low and then uses this stored water to generate electricity by releasing the stored water into a low-level reservoir when electricity demand is high. Such systems are called pump-storage schemes.
Controlling watercourses
Reservoirs can be used in a number of ways to control how water flows through downstream waterways. Downstream water supply – water may be released from an upland reservoir so that it can be abstracted for drinking water lower down the system, sometimes hundred of miles further down downstream. Irrigation – water in an irrigation reservoir may be released into networks of canals for use in farmlands or secondary water systems. Irrigation may also be supported by reservoirs which maintain river flows allowing water to be abstracted for irrigation lower down the river. Flood control – also known as an "attenuation" or "balancing" reservoir, flood control reservoirs collect water at times of very high rainfall, then release it slowly over the course of the following weeks or months. Some of these reservoirs are constructed across the river line with the onward flow controlled by an orifice plate. When river flow exceeds the capacity of the orifice plate water builds behind the dam but as soon as the flow rate reduces the water behind the dam slowly releases until the reservoir is empty again. In some cases such reservoirs only function a few times in a decade and the land behind the reservoir may be developed as community or recreational land. A new generation of balancing dams are being developed to combat the climatic consequences of climate change. They are called "Flood Detention Reservoirs". Because these reservoirs will remain dry for long periods, there may be a risk of the clay core drying out reducing its structural stability. Recent developments include the use of composite core fill made from recycled materials as an alternative to clay. Canals – Where a natural watercourse's water is not available to be diverted into a canal, a reservoir may be built to guarantee the water level in the canal; for example, where a canal climbs to cross a range of hills through locks. Recreation – water may be released from a reservoir to artificially create or supplement white-water conditions for kayaking and other white-water sports. On salmonid rivers special releases (in Britain called freshets) are made to encourage natural migration behaviors in fish and to provide a variety of fishing conditions for anglers.
Flow balancing
Reservoirs can be used to balance the flow in highly managed systems, taking in water during high flows and releasing it again during low flows. In order for this to work without pumping requires careful control of water levels using spillways. When a major storm approaches, the dam operators calculate the volume of water that the storm will add to the reservoir. If forecast storm water will overfill the reservoir, water is slowly let out of the reservoir prior to, and during, the storm. If done with sufficient lead time, the major storm will not fill the reservoir and areas downstream will not experience damaging flows. Accurate weather forecasts are essential so that dam operators can correctly plan drawdowns prior to a high rainfall event. Dam operators blamed a faulty weather forecast on the 2010–2011 Queensland floods. Examples of highly managed Reservoirs are Burrendong Dam in Australia and Llyn Tegid in North Wales. Llyn Tegid is a natural lake whose level was raised by a low dam and into which the River Dee flows or discharges depending upon flow conditions at the time as part of the River Dee regulation system. This mode of operation is a form of hydraulic capacitance in the river system.
Recreation
The water bodies provided by many reservoirs often allow some recreational uses such as fishing, boating, and other activities. Special rules may apply for the safety of the public and to protect the quality of the water and the ecology of the surrounding area. Many reservoirs now support and encourage less informal and less structured recreation such as natural history, bird watching, landscape painting, walking and hiking and often provide information boards and interpretation material to encourage responsible use.

Operation
Water falling as rain upstream of the reservoir together with any groundwater emerging as springs is stored in the reservoir. Any excess water can be spilled via a specifically designed spillway. Stored water may be piped by gravity for use as drinking water, to generate hydro-electricity or to maintain river flows to support downstream uses. Occasionally reservoirs can be managed to retain high rain-fall events to prevent or reduce downstream flooding. Some reservoirs support several uses and the operating rules may be complex. Most modern reservoirs have a specially designed draw-off tower that can discharge water from the reservoir at different levels both to access water as the reservoir draws down but also to allow water of a specific quality to be discharged into the downstream river as compensation water. The operators of many upland or in-river reservoirs have obligations to release water into the downstream river to maintain river quality, support fisheries, maintain downstream industrial and recreational uses or for a range of other requirements. Such releases are known as compensation water.

Pinelands Water Resources
The Pinelands is famous for its vast underground water supply. The Cohansey aquifer in the Pinelands contains over 17 trillion gallons of pure water, enough to cover the entire State of New Jersey with ten feet of water. This underground reservoir feeds most the area's streams, supports its agricultural industry, maintains the ecological balance of our coastal estuaries, and provides drinking water for hundreds of thousands of people. The high water table and porous, sandy soil of the Pinelands make this aquifer particularly vulnerable to pollution. Pollutants move quickly through this sandy soil into the ground water.
To ensure that this water is not substantially degraded, new sewer plants and on-site septic systems must be designed so that discharges do not raise pollution levels on the property to more than two parts per million nitrate-nitrogen. Nitrate-nitrogen, a primary pollutant in the Pinelands, can cause serious health problems and environmental damage.
In some cases, large lots are required to dilute pollutants from septic systems. In other cases, innovative septic systems must be used to reduce the level of pollutants entering the ground water. Septic systems must be installed above the water table (the point below ground where water begins) to function properly and prevent pathogens from entering the ground water. Construction is generally prohibited in areas where the ground water is within five feet of the surface during the wettest part of the year.
Another major feature of the Pinelands Plan relates to the retention of storm water. Because of the porous soils here, most rainwater percolates through the soil and replenishes the ground water system. However, development normally reduces the amount of water drained into the aquifer unless special measures such as swales or retention basins are used. Unfortunately, storm sewers normally only carry water away and discharge it into a stream. This results in a lowering of the ground water level and introduces pollutants directly into streams. The Pinelands Plan, therefore, requires that increased storm water run off caused by development be retained on site.
There are a number of other standards which are designed to protect the region's water resources (e.g., minimum well depths), prohibitions on the disposal of toxic chemicals, and limits on the exportation of water outside of the Pinelands.

Terms

Hydrology is the study of the distribution and movement of water. The unusual shaped spillway regulates the lake's level (stage) by allowing the discharge (flow) to vary throughout the seasonal changes in the watershed. This prevents erosion of the area along the streams and the lake's shore.
Headwater - The upstream portion of a watershed.
Reservoir (pool) level - The elevation of the water in a reservoir at a given time, measured in feet above sea level.
Top of gates - The maximum controlled elevation at a project, typically the top of a spillway gate in a closed position or crest elevation of an uncontrolled outlet structure.
Spillway - A channel or passageway around or over a dam through which water is released, or "spilled," past the dam. Spillways at some dams are controlled with gates. At others, water flows over the top of the spillway automatically when the reservoir level gets to a certain elevation. A spillway is a safety valve for a dam; it can be used to discharge rainfall and runoff from major storms as necessary to maintain the reservoir below a predetermined maximum level.
CFS - Cubic feet per second, typically used as a measure of flow in a stream. A cubic foot is equivalent to about 7.5 gallons. A measure of 1,000 cfs is equal to about 7,500 gallons of water per second
Tailwater - The part of a river downstream from a dam, where the flow and quality of the water are substantially affected by the dam's discharge.


There is no need to enter Harry Wright Lake Park since there is free parking in the dirt lot on the east side of Lake Rd. If you did want to explore the headwater where the lake originates, a beach badge is required to enter the beach area and nearby parking during the summer months (Memorial Day through Labor Day), but I think they only check between 9am and 6pm, so we normally go earlier/later than those hours to avoid the fee.

To Log this Earthcache, you must complete the following and email to the CO when you post your find (a response will only be sent if there is a problem):
1. From the posted coords, survey the layout of the lake. What type of reservoir would you classify this as (Valley Dammed, Bank-Side, Service, a Combination, etc.)?
2. What do you conclude the uses of this particular reservoir would be (Direct Water Supply, Hydroelectricity, Controlling Watercourses, Flow Balancing, Recreation, a Combination, etc.)?
3. Use your GPS to measure how many feet above sea level is it at the spillway (posted coords).
4. Optional - Post a photo of you and/or your GPS at GZ. Especially if you were fortunate enough to arrive there around sunset. It's a great view!
Enjoy!

Additional Hints (No hints available.)



Advertising with Us

Inventory

There are no Trackables in this cache.

View past Trackables

What are Trackable Items?

Bookmark Lists

View all bookmark lists...