leads to a monetary damage function. The damage function is thus obtained from the estimated
relationship between dose and effect after an
economic price has been attributed to each
degraded physical unit.
The damage function method, like all methods
of monetary valuation of physical effects, is
carried out in three fundamental stages. Firstly,
the physical effect of environmental change on
the receiver (real estate, natural resources,
machinery or persons affected by the modification) is estimated. In the case of Lake Lagdo, this
relationship was established by the study commissioned by MEADEN in 2005. This study
revealed a sediment deposit of about 40.80 million cubic meters each year, which potentially
implies the loss of a volume of water of the same
order. Secondly, a quantitative causality link is
established between a change in the environment
and its consequences on production or costs. In
the second step, a quantitative link between lake
sedimentation and its effects on the storage
capacity of the reservoir must be established.
This step requires estimation of the amount of
electrical energy that would be lost each year by
the depreciation of the reservoir of 40.80 million
cubic meters of water lost due to sediment
deposition in the lake. Based on the study by
(Cruz et al. 1988), which estimated the off-site
costs of sedimentation of the dam reservoir in the
Magat and Pantabangan watersheds in the
Philippines, we can determine the volume of
water needed to generate the kilowatt hour of
electricity. Thirdly, the economic value of these
impacts is estimated by estimating the market
value of these impacts on production or costs. It
is a question of associating a monetary value to
the link ascertained in the second step. In other
words, the quantified damage, in this case, the
loss of electrical energy is evaluated by assigning
a value to it based on the price of electricity on
the market.
2.2.2 Description of the Variables
The description of the variables to be used for the
estimation requires first an explanation of some
notions that are relevant in understanding the
impact of sedimentation in artificial lakes.
Dead storage capacity and live storage
capacity: The storage capacity of the lake is
divided into live storage capacity and dead storage capacity. The dead storage capacity is at the
bottom of the reservoir and it is part of the total
capacity of the reservoir that is allocated to
sediment storage (Cruz et al. 1988). Usually,
engineers plan a certain amount of dead storage
in a dam reservoir based on existing sedimentation rates, with the remaining storage capacity
assumed to be active. An unexpected increase in
sedimentation due to soil erosion upstream is
assumed to increase the components of the dead
storage of a reservoir. This means that the more
active storage becomes inactive and therefore,
there is a loss of water available for hydraulic
power, irrigation and other economic benefits.
The direct storage capacity is above the tank.
The storage of water in the direct reservoir can be
used to supply water for hydroelectric power,
irrigation, etc. Sedimentation can reduce the
direct storage capacity of a reservoir resulting in
the loss of economic benefits. The tank, therefore, plays the role of an accumulator of energy
(Cruz et al. 1988). Consequently, any reduction
in the live storage will impair the performance of
the associated plant by reducing the energy
capacity and the maximum power available
during the most critical periods of consumption
at the time of inadequate flows. With siltation of
the tank, soil erosion reduces the hydroelectric
potential and thus the potential benefits of the
Lagdo power plant. This reduction in potential
profits is expressed in terms of reduced tank
capacity. Table 1 shows the capacity of these
tanks for Lake Lagdo.
To cover its annual production, the plant
needs a volume of water that is at the level of the
normal coast (216 m asl), i.e., a volume of water
equivalent to 4.57 billion cubic meters. The
minimum water level is 206 m. If the volume of
water falls short of this level, there will be no
electricity production. If the maximum elevation
of the lake level is 218.18 m asl, the Reliability
Centered Maintenance (RCM) bathymetric measurements in 2004 show the lowest coasts of the
current floor at 194 m asl, a maximum depth of
24.18 m. Also, turbine management is
98
D. Y. Ngondjeb and E. Ayuk
relationship between dose and effect after an
economic price has been attributed to each
degraded physical unit.
The damage function method, like all methods
of monetary valuation of physical effects, is
carried out in three fundamental stages. Firstly,
the physical effect of environmental change on
the receiver (real estate, natural resources,
machinery or persons affected by the modification) is estimated. In the case of Lake Lagdo, this
relationship was established by the study commissioned by MEADEN in 2005. This study
revealed a sediment deposit of about 40.80 million cubic meters each year, which potentially
implies the loss of a volume of water of the same
order. Secondly, a quantitative causality link is
established between a change in the environment
and its consequences on production or costs. In
the second step, a quantitative link between lake
sedimentation and its effects on the storage
capacity of the reservoir must be established.
This step requires estimation of the amount of
electrical energy that would be lost each year by
the depreciation of the reservoir of 40.80 million
cubic meters of water lost due to sediment
deposition in the lake. Based on the study by
(Cruz et al. 1988), which estimated the off-site
costs of sedimentation of the dam reservoir in the
Magat and Pantabangan watersheds in the
Philippines, we can determine the volume of
water needed to generate the kilowatt hour of
electricity. Thirdly, the economic value of these
impacts is estimated by estimating the market
value of these impacts on production or costs. It
is a question of associating a monetary value to
the link ascertained in the second step. In other
words, the quantified damage, in this case, the
loss of electrical energy is evaluated by assigning
a value to it based on the price of electricity on
the market.
2.2.2 Description of the Variables
The description of the variables to be used for the
estimation requires first an explanation of some
notions that are relevant in understanding the
impact of sedimentation in artificial lakes.
Dead storage capacity and live storage
capacity: The storage capacity of the lake is
divided into live storage capacity and dead storage capacity. The dead storage capacity is at the
bottom of the reservoir and it is part of the total
capacity of the reservoir that is allocated to
sediment storage (Cruz et al. 1988). Usually,
engineers plan a certain amount of dead storage
in a dam reservoir based on existing sedimentation rates, with the remaining storage capacity
assumed to be active. An unexpected increase in
sedimentation due to soil erosion upstream is
assumed to increase the components of the dead
storage of a reservoir. This means that the more
active storage becomes inactive and therefore,
there is a loss of water available for hydraulic
power, irrigation and other economic benefits.
The direct storage capacity is above the tank.
The storage of water in the direct reservoir can be
used to supply water for hydroelectric power,
irrigation, etc. Sedimentation can reduce the
direct storage capacity of a reservoir resulting in
the loss of economic benefits. The tank, therefore, plays the role of an accumulator of energy
(Cruz et al. 1988). Consequently, any reduction
in the live storage will impair the performance of
the associated plant by reducing the energy
capacity and the maximum power available
during the most critical periods of consumption
at the time of inadequate flows. With siltation of
the tank, soil erosion reduces the hydroelectric
potential and thus the potential benefits of the
Lagdo power plant. This reduction in potential
profits is expressed in terms of reduced tank
capacity. Table 1 shows the capacity of these
tanks for Lake Lagdo.
To cover its annual production, the plant
needs a volume of water that is at the level of the
normal coast (216 m asl), i.e., a volume of water
equivalent to 4.57 billion cubic meters. The
minimum water level is 206 m. If the volume of
water falls short of this level, there will be no
electricity production. If the maximum elevation
of the lake level is 218.18 m asl, the Reliability
Centered Maintenance (RCM) bathymetric measurements in 2004 show the lowest coasts of the
current floor at 194 m asl, a maximum depth of
24.18 m. Also, turbine management is
98
D. Y. Ngondjeb and E. Ayuk