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In water-related science and engineering, there are two similar but distinct definitions in use for the word drawdown:

• In subsurface hydrogeology, drawdown is the reduction in hydraulic head observed at a well in an aquifer, typically due to pumping a well as part of an aquifer test or well test.
• In surface water hydrology and civil engineering, drawdown refers to the lowering of the surface elevation of a body of water, the water table, the piezometric surface, or the water surface of a well, as a result of the withdrawal or water.^[1]

In either case, drawdown is the change in hydraulic head or water level relative to the initial spatial and temporal conditions of the system. Drawdown is often represented in cross-sectional diagrams of aquifers. A record of hydraulic head, or rate of flow (discharge), versus time is more generally called a hydrograph (in both groundwater and surface water). The main contributor to groundwater drawdown since the 1960s is over-exploitation of groundwater resources.^[2]

Definition: In financial technical analysis, a drawdown is a method used to measure the financial risk of an investment. Simply put, it is the extent or the amount of losses carried by a financial instrument since it starts to decline from a high point until it bounces back to surpass such point. What Does Drawdown. Each Drawdown Notice shall contain summary details of any proposed Investment to which it relates (if any), including the nature of the business carried on by the proposed Portfolio Company and confirmation by the Manager that the proposed Investment falls within the Investment Policy, if necessary giving reasons for such conclusion. Drawdown is one of the most important and widely used mathematical technologies used by the analyst to analyze the performance of the stock or the fund or the fund based upon drawdown%. Investors will always prefer investing in a stock, or the fund will lower drawdowns history in the past as it directly hits the performance of the fund managers.

“ Drawdown is an exceptional example of cooperation between some of the sharpest thinkers on climate and energy matters, an atlas that has the potential to save the planet.” —Andreas Kuhlmann, CEO German Energy Agency “It will give you the best kind of hope, the kind that balances realism with radical vision. Drawdown is in its 14th printing, was a NYT bestseller, is published in 14 languages, has been referred to and used by heads of state, is part of the curriculum on every grade level from 4th grade to MIT graduate school, and is placed in a New Zealand hotel chain alongside the Gideon Bible. Drawdown named the goal.

Drawdown occurs in response to:

1. pumping from the bore
2. interference from a neighbouring pumping bore
3. in response to local, intensive groundwater pumping
4. regional seasonal decline due to discharge in excess of recharge^[3]

Terminology[edit]

• Aquifer is an underground layer of permeable rock or sand, that hold or transmit groundwater below the water table that yield a significant supply of water to a well.^[4]
• Aquifer test (or a pumping test) is a field experiment in which a well is pumped at a controlled rate and the aquifer's response (drawdown) is measured in one or more observation wells.^[5]
• Cone of depression is a conically-shaped depression that is produced in a water table as a result of pumping water from a well at a given rate.^[4]
• Groundwater is water located beneath the earth's surface in pores and fractures of soil and rocks.^[6]
• Hydraulic head (or piezometric head) is a specific measurement of the potential of water above a vertical datum.^[7] It is the height of the free surface of water above a given point beneath the surface.^[4]
• Pumping level is the level of water in the well during pumping.^[8]
• Specific capacity is the well yield per unit of drawdown.^[8]
• Static level is the level of water in the well when no water is being removed from the well by pumping.^[8]
• Water table is the upper level of the zone of saturation, an underground surface in which the soil or rock is permanently saturated with water.^[9]
• Well yield is the volume of water per unit time that is produced by the well from pumping.^[8]

Methods for measuring drawdown[edit]

• Transducers are used to measure water levels in groundwater wells, rivers, streams, tanks, open channels and lift stations.^[10]
• Acoustic well sounders or echometers are a simple, cost effective, and minimally intrusive tool used to measure subsurface pressures and levels.^[11]
• Electric sounders are a practical land cost-effective method used to measure well water levels.^[12] This method uses a weight attached to a stranded insulated wire and an ammeter to indicate a closed circuit. Current supplied from a small battery flows through the circuit when the tip of the wire is in contact with the surface of the water.^[13]
• Air line method is a convenient and nonintrusive method used to measure water levels that is often used for the repeated testing of wells over 300 feet deep.^[13] This method obtains water table depth using a pressure gauge and water displacement.^[14]
• Wetted tape method is a commonly-used method for measuring water levels up to roughly 90 feet deep. This method uses a lead weight attached to a steel measuring tape.^[13]

Drawdown Fund

Ecological impacts of groundwater drawdown[edit]

Groundwater drawdown due to excessive water extraction can have adverse ecological impacts. Groundwater environments often have high biodiversity, however, drawdown alters the amount and types of nutrients released to surrounding organisms.^[15] In addition, nearby wetlands, fisheries, terrestrial and aquatic habitats may be altered with a reduction in the water available to these ecosystems, sometimes altering species ecophysiology.^[16]

Extracting groundwater at a rate that is faster than it can be naturally replenished is often referred to as overdrafting. Overdrafting may decrease the amount of groundwater that naturally feeds surrounding water bodies, including wetlands, lakes, rivers and streams.^[17] Additionally, when a cone of depression is formed around a pumping well due to groundwater extraction, nearby groundwater sources may flow toward the well to replenish the cone, taking water from local streams and lakes. This may result in poor water quality in these local water bodies as baseflow water contribution is reduced, which could result in perennial streams becoming more intermittent, and intermittent streams becoming more ephemeral. Finally, drawdown from groundwater extraction may lead to an increased sensitivity of the ecosystem to climate change and may be a contributing factor to sea-level rise and land subsidence.^[17]

Related[edit]

References[edit]

Afghanistan Drawdown

1. ^'Glossary of Hydrologic Terms'. www.nws.noaa.gov. Retrieved 2019-03-19.
2. ^Mirnezami, S.J.; Bagheri, A.; Maleki, A. (2018). 'Inaction of Society on the Drawdown of Groundwater Resources: A Case Study of Rafsanjan Plain in Iran'. Water Alternatives. 11 (3): 725–748 – via Content Server.
3. ^Lytle, Michael J.; Markowski, Paul (1989). 'An Introduction to Well Drawdown'(PDF). Retrieved March 17, 2019.
4. ^ ^abc'Glossary of Hydrologic Terms'. www.nws.noaa.gov. Retrieved 2019-03-19.
5. ^'Pumping Tests :. Aquifer Testing 101'. www.aqtesolv.com. Retrieved 2019-03-17.
6. ^Groundwater Terms and Definitions(PDF), Goulbourn-Murray Water, p. 34, retrieved 2019-03-17
7. ^'Potential Energy and Hydraulic Head | EARTH 111: Water: Science and Society'. www.e-education.psu.edu. Retrieved 2019-03-18.
8. ^ ^abcdLytle, Michael J.; Markowski, Paul (1989). 'An Introduction to Well Drawdown'(PDF). Retrieved March 17, 2019.
9. ^'Water table | hydrology'. Encyclopedia Britannica. Retrieved 2019-03-18.
10. ^'Water Level Sensor or Submersible Pressure Tranducer'. www.globalw.com. Retrieved 2019-10-19.
11. ^'Acoustic Well Sounders'. www.fekete.ca. Retrieved 2019-04-01.
12. ^Alberta Agriculture Food and Rural Development (2012). 'Making and Using an Electric Sounder to Monitor Water Wells'(PDF). Government of Alberta.
13. ^ ^abcwellcare®. 'Determining Static Water Level in a Well'(PDF). Water Systems Council.
14. ^Henggeler, Joe. 'INSTALLING AN INEXPENSIVE AIR LINE TO MEASURE WATER DEPTHS IN WELLS'(PDF). Missouri Crop Resource Guide. Archived from the original(PDF) on 2019-04-01.
15. ^Department of the Environment and Energy (2018). 'What are the ecological impacts of groundwater drawdown?'(PDF). Government of Australia.
16. ^Antunes C, Chozas S, West J, et al. Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi‐arid coastal ecosystem. GlobChange Biol. 2018;24:4894–4908. https://doi.org/10.1111/gcb.14403
17. ^ ^ab“Environmental Impacts of Water Withdrawals and Discharges in Six Great Lakes Communities: A Role for Green Infrastructure”, J. W. Ridgway, R. Higuchi, L. Hoffman, and R. Pettit, Environmental Consulting & Technology Inc. Report, 45 pp, May 2016

Drawdown Definition