combined storage capacity of about 575 km
3
(Tigrek and Aras 2012). The financial costs and
human resources required to construct reservoirs
are enormous. In addition, there is socioeconomic and environmental disruption brought
about by the construction of dams to the local
populace lifestyles. Most countries, especially
developing, rely on external funding in the form
of grants or loans to offset the cost of developing
their reservoir capacities.
Despite the benefits and enormous cost of
constructing reservoirs, most natural lakes and
reservoirs are currently threatened by sedimentation. Reservoirs are designed to have a given
lifespan, where they offer useful services, after
which they are supposed to be rehabilitated or
decommissioned. However, sedimentation drastically reduces this lifespan. According to Wisser
et al. (2013) sedimentation, which results in
volume loss, controls the lifespan of reservoirs
since it occurs faster than the loss of structural
integrity of the dam wall. Globally, about 31 km
3
of reservoir volume is lost annually to sedimentation and this could deplete half of the current
reservoir’s capacity by 2100 (Sumi et al. 2004).
According to Palmieri et al. (2003), the worldwide annual loss of reservoir storage capacity can
be associated with the need for 45% additional
reservoir capacity. This additional capacity is
estimated to cost about US$ 13 billion per year
(Palmieri et al. 2003). With capacity loss due to
sedimentation, hydropower generation is also
affected. On the other hand, sedimentation not
only leads to capacity loss but also results in
degradation of water quality, hence increases the
costs of water treatment in the case of drinking
water reservoirs.
The loss of volume in the reservoir is related
to food production activities upstream—and in
general with watershed management, which
includes water, soil and land-use. At the source,
mainly farmland, the costs are also discernible.
The upstream farmers lose their fertile top soil to
agents of erosion. The productive top layer is lost
and consequently, the cost of food production
goes up. This includes the expensive fertilizers
applied to improve farm productivity.
Consequently, farm income declines. If
unchecked, it becomes a vicious cycle of loss,
thus the more soil the farmer loses, the more
fertilizer will be required to raise production.
Therefore, it is imperative to quantify the nexus
between food production and water quantity
downstream and the ability of reservoirs to sustainably supply water and/or generate electricity.
Similar nexus assessments have been done in
other parts of SSA (e.g., Karlberg et al. 2015).
Controlling erosion upstream remains the
most viable option for sedimentation control.
Compared to the cost of dredging, scouring and
trucking, upstream conservation remains the
most viable measure (Kawashima et al. 2003).
Conservation measures have been used to control
erosion into major dams worldwide with or
without reward schemes to the farmers. For
instance, a study in Sasumua watershed, Kenya,
showed that farmers under Payment for Environmental Services (PES) can significantly
reduce sediment load into the reservoir as indicated by an observed decline of average Total
Suspended Solids (TSS) from 71.05 mg/L to an
average TSS of 42.73 mg/L in the inflow rivers
(Nduhiu et al. 2016). The adoption of PES
schemes has increased the chances of success in
erosion control in Sasumua and other parts of the
world (Dougill et al. 2012; Nduhiu et al. 2016).
Unlike upstream erosion control, dredging has
the capability of restoring the storage capacity of
reservoirs where deposited sediment is removed.
However, studies in the United States indicated
that the cost of dredging might be twice as high
as the cost of developing new reservoirs (Alan
Plummer Associates et al. 2005). Thus, upstream
erosion control remains one of the most viable
options for sedimentation control in reservoirs
and lakes in Kenya.
This paper gives information about the
assessment of sedimentation rates of reservoirs in
Kenya and identifies challenges and constraints
to the assessment. The paper also evaluates how
multifunctional historical data can be generated
from sedimentation assessment via Bathymetric
Survey System to inform the nexus of food
production and water management.
82
J. Sang and C. Maina
3
(Tigrek and Aras 2012). The financial costs and
human resources required to construct reservoirs
are enormous. In addition, there is socioeconomic and environmental disruption brought
about by the construction of dams to the local
populace lifestyles. Most countries, especially
developing, rely on external funding in the form
of grants or loans to offset the cost of developing
their reservoir capacities.
Despite the benefits and enormous cost of
constructing reservoirs, most natural lakes and
reservoirs are currently threatened by sedimentation. Reservoirs are designed to have a given
lifespan, where they offer useful services, after
which they are supposed to be rehabilitated or
decommissioned. However, sedimentation drastically reduces this lifespan. According to Wisser
et al. (2013) sedimentation, which results in
volume loss, controls the lifespan of reservoirs
since it occurs faster than the loss of structural
integrity of the dam wall. Globally, about 31 km
3
of reservoir volume is lost annually to sedimentation and this could deplete half of the current
reservoir’s capacity by 2100 (Sumi et al. 2004).
According to Palmieri et al. (2003), the worldwide annual loss of reservoir storage capacity can
be associated with the need for 45% additional
reservoir capacity. This additional capacity is
estimated to cost about US$ 13 billion per year
(Palmieri et al. 2003). With capacity loss due to
sedimentation, hydropower generation is also
affected. On the other hand, sedimentation not
only leads to capacity loss but also results in
degradation of water quality, hence increases the
costs of water treatment in the case of drinking
water reservoirs.
The loss of volume in the reservoir is related
to food production activities upstream—and in
general with watershed management, which
includes water, soil and land-use. At the source,
mainly farmland, the costs are also discernible.
The upstream farmers lose their fertile top soil to
agents of erosion. The productive top layer is lost
and consequently, the cost of food production
goes up. This includes the expensive fertilizers
applied to improve farm productivity.
Consequently, farm income declines. If
unchecked, it becomes a vicious cycle of loss,
thus the more soil the farmer loses, the more
fertilizer will be required to raise production.
Therefore, it is imperative to quantify the nexus
between food production and water quantity
downstream and the ability of reservoirs to sustainably supply water and/or generate electricity.
Similar nexus assessments have been done in
other parts of SSA (e.g., Karlberg et al. 2015).
Controlling erosion upstream remains the
most viable option for sedimentation control.
Compared to the cost of dredging, scouring and
trucking, upstream conservation remains the
most viable measure (Kawashima et al. 2003).
Conservation measures have been used to control
erosion into major dams worldwide with or
without reward schemes to the farmers. For
instance, a study in Sasumua watershed, Kenya,
showed that farmers under Payment for Environmental Services (PES) can significantly
reduce sediment load into the reservoir as indicated by an observed decline of average Total
Suspended Solids (TSS) from 71.05 mg/L to an
average TSS of 42.73 mg/L in the inflow rivers
(Nduhiu et al. 2016). The adoption of PES
schemes has increased the chances of success in
erosion control in Sasumua and other parts of the
world (Dougill et al. 2012; Nduhiu et al. 2016).
Unlike upstream erosion control, dredging has
the capability of restoring the storage capacity of
reservoirs where deposited sediment is removed.
However, studies in the United States indicated
that the cost of dredging might be twice as high
as the cost of developing new reservoirs (Alan
Plummer Associates et al. 2005). Thus, upstream
erosion control remains one of the most viable
options for sedimentation control in reservoirs
and lakes in Kenya.
This paper gives information about the
assessment of sedimentation rates of reservoirs in
Kenya and identifies challenges and constraints
to the assessment. The paper also evaluates how
multifunctional historical data can be generated
from sedimentation assessment via Bathymetric
Survey System to inform the nexus of food
production and water management.
82
J. Sang and C. Maina