Title: Optimal Yield
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Permanent Link: http://ufdc.ufl.edu/WL00001849/00001
 Material Information
Title: Optimal Yield
Physical Description: Book
Language: English
Publisher: American Geophysical Union
 Subjects
Spatial Coverage: North America -- United States of America -- Florida
 Notes
Abstract: Optimal Yield Definition Groundwater Management: The Use of Numerical Models
General Note: Box 9, Folder 7 ( SF-Safe Yield - 1956-1995 ), Item 2
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
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Bibliographic ID: WL00001849
Volume ID: VID00001
Source Institution: Levin College of Law, University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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10 Groundwater Management: The Use of Numerical Models

Remedial measures being tried or contemplated include (1) encouragement of water-
saving practices and managed production, (2) administrative regulation of with-
drawals, (3) artificial recharge of pond water, (4) importation of water, and (5) tax
relief in the form of a depletion allowance for the waning resource. -
This case-history discussion was adapted in part from a paper by S. W. Lohman.
The interested reader is referred to that paper for additional description of the
southern High Plains water situation. The paper also includes several other selected
cases of ground-water development under various conditions of hydrology and
geology, and description of the management programs adopted [Water Resources
Council, 1973]. -

Optimal Yield
Planning for long-term development of ground-water reservoirs and sustained
yield often focuses on concepts of "safe yield" and "mining." Many definitions of
these terms have been advanced. Any useful concept of safe yield for a ground-water
system requires that quantitative values for yield be established within the
framework of (A) the principle of continuity and (B) precise definition of the extent
to which side effects or undesirable results will be tolerated. Accordingly, the safe
yield of a ground-water reservoir usually is not a single, fixed rate of withdrawal but
is a variable rate that depends upon many complexly interrelated factors of which
the hydrologic conditions may be only one of many.
If the conditions of safe yield can be defined for a given reservoir-development
plan, it may be a useful concept in evaluating the possible alternatives of manage-
ment approaches. However, in practice, the concept is difficult to apply and has
been greatly misused. Unless the term can be explicitly defined for a particular case,
it will inhibit effective planning. The logic of safe yield is elusive and its use appears
to be declining. The term "mining," perhaps representing the antonym of safe yield,
is similarly vague in concept and has only limited utility. For this term, too, explicit
definition for a particular reservoir may be necessary.
Recently, the broad concept of "optimal yield" was introduced to replace safe
yield and mining yield. Optimal yield is defined as the optimal plan for the use of a
ground-water supply. It is a plan for realization of the maximum economic objec-
tives of a ground-water development subject to physical, chemical, legal, and other
constraints on the use of the reservoir. As defined, the optimal yield is a function of
time and of the state of the entire system, rather than simple specifications of
allowable pumping rates alone as is commonly the case with most safe yield and
mining concepts. For a given development, optimal yield will not necessarily require
sustained yield. Large withdrawals in excess of equilibrium limits may be the op-
timal developmental plan under this concept [Water Resources Council, 1973].
Optimal development of a groundwater resource implies an efficient balance between
supply and demand. It further implies, or it should, that net benefits reflect en-
vironmental costs as well as the more traditional capital, operation, and maintenance
costs. The benefits of groundwater development must be tempered with its potentially
attendant environmental impacts.
Exploitation of the resource, particularly if it is mined, may lead to land subsidence,
the gradual collapse of the land surface that may result if the pumping is excessive
enough to lower groundwater heads. As a result of land subsidence, buildings, roads,
and water and sewer mains may be damaged and the surface drainage pattern altered,
adversely affecting surface runoff.
Groundwater provides the base flow of streams and often plays a dominant role in
determining the quality of surface water, particularly during periods of low flow. Along
coastal reaches, groundwater development may lead to the lowering of the freshwater
head of the system with the consequent intrusion of salt water.
As environmental issues have become translated into development objectives,
groundwater modeling has become a more demanding task. Less well understood are
the geochemical properties of aquifers and the manner in which pollutants are
transported and affect the properties. Nonetheless, appropriate models have been

















10 Groundwater management: The Use of Numerical Models

Remedial measures ein tried or contemplated include (1) encouragement of water-
savin practices and production (2) administrative regulation of with-
drawals, (3) artificial re of pond water, (4) Importaton of water, and (5) tax
relief in the form of a n allowance for the waning resource. --
This case-history nwas adapted in part from a paper by S. W. Lohman.
f The interested reader s referred to that paper for additional description of the
southern High Plains wa situation. The paper also Includes several other selected
cases of Sround-water m under various conditions of hydrology and
-sgology, and descriptio of the management programs adopted (Water Raeourer
SCounc,. 19731. :.

Optimal Yield
Planning for long-te development of round-water reservoirs and sustained
yield often focuses on concepts of "safe yield" and "mning." Many definitions of
these terms have been advanced. Any useful concept of safe yield for a ground-water
System requires that qutitative values for yield be established within the
framework of (A) the op f continuity and (B) precise definition of the extent
to which side effects or undesirable results will be tolerated. Accodingly, the safe
y field of a ground-water reservalr usually is not a single, fixed rate of withdrawal but
is a variable rate that depends upon many complexly Interrelated factors of which
the hydrologic conditions may be only one of many. .,
SIf the conditions of safe yield can be defined for a given reservoi-development
plan, It may be a useful ocept in evaluating the possible alternatives of manage-
ment approaches. How n practice, the concept is difficult to apply and has
been greatly misused. U the term can be explicitly defined for a particular case,
it will inhibit effective The logic of safe yield is elusive and ts use appears
to be declining. The term' ," perhaps representing the antonym of safe yield,
is similarly vague in onpand has only limited utility. For this term, too, explicit
definition for a reservoir may be necessary.
Recently, the broad oep of "optimal yield" was Introduced to replace safe
yield and mining yield. yield is defined as the optimal plan for the use of a
ground-water supply. It a plan for realization of the maximum economic objec-
tives of a ground-water elopment subject to physical, chemical, legal, and other
constraints on the use of reservoir. As defined, the optimal yield is a function of
time and of the state of the entire system, rather than simple specifications of
allowable pumping rates as is commonly the case with most safe yield and
mining concepts. For a g development, optimal yield will not necessarily require
sustained yield. Large wit iwals n excess of equilibrium limits may be the op-
timal developmental plan r this concept [Water Resowur Council, 1973].
Optimal development of a groundwater resource implies an efficient balance between
supply and demand. It further implies, or it should, that net benefits reflect en-
vironmental costs as well as te more traditional capital, operation, and maintenance
costs. The benefits of ground ater development must be tempered with its potentially
attendant environmental imp .
Exploitation of the resource particularly if it is mined, may lead to land subsidence,
the gradual collapse of the nd surface that may result if the pumping is excessive
enough to lower groundwater heads. As a result of land subsidence, buildings, roads,
and water and sewer mains m y be damaged and the surface drainage pattern altered,
adversely affecting surface off.
Groundwater provides the ase flow of streams and often plays a dominant role in
determining the quality of suri e water, particularly during periods of low flow. Along
coastal reaches, groundwater levlopment may lead to the lower the he freshwater
head of the system with the nsequent intrusion of salt water.
As environmental issues iave become translated into development objectives,
groundwater modeling has beme a more demanding task. Less well understood are
the geochemical properties f aquifers and the manner in which pollutants are
transported and affect the p operties. Nonetheless, appropriate models have been




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