National Hydrology committee of Afghanistan (NHCA ...

National Hydrology committee of
Afghanistan (NHCA)
Sedimentation in Reservoire
OCt.2007
Prof. Mohammad Qasem Seddeqy
KPU

بسم االله الرحمن الرحيم
وجعلنامن الماءکل شئء حی
30
واز آب هر چيزی رازنده گردانيدیم سوره انبيا ایه

Classification of Rivers according to
the topography of the river basin
‣ Upper reaches in the hilly region
‣ Lower reaches in the alluvial plain
Rivers on alluvial plains may be broadly classified in
to three types:
1. The meandering type
2. The aggrading type
3. The degrading type

Sediment is fragmental material,
primarily formed by the physical
and chemical disintegration of
rocks from the earth crust.
The process of moving and
removing from their original
source or resting place is called
erosion

Why a good understanding of sediment
transport processes is indispensable
1. Morphological boundary condition for
design of Hydraulic structure and river
training works
2. Sedimentation in reservoirs
3. Sediment problems at Intakes
4. Environmental Impact assessment

Origin and types of Sediment
‣ Cohesive
‣ Non Cohesive
Cohesive sediment – the physical- chemical
interaction between particles plays a
significant role.
Non Cohesive sediment – there is no
physical and chemical interaction between
individual particles .

Sediment Control Plan
Q
Control Point
(Q+A-B)*α
B
A
E
C
D
Target Area
‣ E=(Q+A - B)(1 -α) - C - D

Sediment Control Plan
‣ E=(Q+A - B)(1 -α) - C - D
• E : Design allowable sediment discharge
• Q : Design sediment discharge at the design
control point of the upstream end of the
subject sub-basin
basin
• A : Design sediment production
• B : Design reduction of sediment production
• α : Ratio of volume of channel sediment
mitigation
• C : Design reduction of sediment discharge
• D : Design mitigation volume of sediment
discharge

Sediment Control Dam
‣ Function 1: To Stabilize
Hillside Slopes
Scouring force
becomes less than
before;
Shallower in depth,
Slower in velocity

Sediment Control Dam
‣ Function 1 To Reduce Sediment
Discharge
Sediment Capacity
for Flood Period
Initial Sediment
Capacity

Sediment Control Dam
‣ Function 2: To Mitigate Streambed
Erosion by milder bed-slope with
Stepwise Dams
L
h
m
n
1
1
m>n
L=((m*n)/(m - n))*h

Sediment Control Dam
‣ Function 3: To Mitigate Sediment
Runoff
Design Sedimentation Line
to Cover the Unstable
Sediment Deposition
Unstable Sediment
Deposition

3D VIEW OF KABUL RIVER BASIN
Kabul
Naghlu
dam
Oulet basin

3D View of Alingar River
Basin
Darunta
Dam

Other view from agriculture land of
Gulbahar –Panjsheer desert

3D view of Sorobi and Naglu
dams
Naghlu dam
Sorobi
dam

3D View of from Kunar River
Kunar river
Pakistan
Darunta
dam

3D View of Darunta Dam
2002-09-
Darunta
dam
: Date
Landsat 7 satalite
22

3D View of Panjsheer river
Basin
Gulbahar
desert
Naghlu
dam
Darunta
dam

Darunta Reservoir 24
years ago
1979-06-
: Date Landsat 3 satalite
20

•Sedimentation
‣ Intensive soil erosion has been causing
rapid sedimentation of reservoirs with
an important loss of irrigation lands,
power generation capacity and life time
of reservoirs
‣ Afganistan is facing annually with 150
million m3 sedimentation in the
reservoirs and 400 million m3
sedimentation to downstream of dam
reservoirs and irrigation networks

Causes of sedimentation
‣ Desertification
1. Continued deforestation from logging and fuel wood needs : In
South,east and northeast of Afghanistan.
2. overgrazing:The grazing lands used by Kochis (nomads)have
been dried out due to the lack of sufficient rainfalls & converting to
cultivable land causing considerable reduction in livestock and
livelihood.
3. Destroying land covers bush used for fuel wood
4. Soil erosion due to flood and wind
5. Unsustainable agriculture :Salinization:
of soil ,over use of
agricultural inputs.
6. Drought :Started in 1969,getting up to a critical status in 1997-
2002 ,causing hydrological circulations of the soil

‣ Lack of river mangement and training work
‣ Land use
‣ steep drainage basin slopes and relief
‣ high rainfall magnitudes and frequencies
‣ Lack of Reservoir maintenance

Extensive
destruction of
forest over the
past 25 years

Sedimentation and erosion
problems affect the following
sectors.
‣ Health(drinking water , domestic )
‣ Society
‣ Economy(Water
supply,Irrigation,Hydropower,Maintenance
and operation of
Reservoir,Navigation
Navigation,Flood
Protection,Fishery
)
‣ Environment

Flash flooding is a direct
consequence of land cover
degradation in Balkh river
26 March, 2003

Sediment deposition into reservoirs
has several major detrimental
effects.
‣ Loss of storage capacity.
‣ Damage to or impairment of hydro equipment.
‣ Bank erosion and instabilities.
‣ Downstream channel modification.
‣ Reduced downstream suspended sediment load.
‣ Upstream aggradations.
‣ Effect on water quality.
‣ Effect on waste assimilation.
‣ Effect on navigation and recreation.
‣ Effect on aquatic life.

Plans for mitigation of erosion and
sedimentation
‣ For urgently Dredging, Sub cut, empty washing
‣ Reforestation and plantation for land covering long term
‣ Preparation of National Strategy and policy for
erosion and sediment mitigation.
‣ Use water resource potential in the country through
rain and flood water harvesting, construction of
small, medium, and large depressions, pools and
dams for flood control and prevention of erosion .
‣ Construction of protective structures along river
where sliding may occur.

Immediate Response
‣ Good river management :includes sediment and
floodplain management
‣ National Emergency Employment Program,
National Solidarity Program and National
Hydrology program of Afghanistan (NHCA),
Based Development program and other
Nationwide programs are contributing to Erosion
and sedimentation relief
‣ Emergency Rehabilitation Irrigation Project
(Hydraulic structures)
‣ Intermittent meetings by UN and Governmental
and well-known non-Governmental Agencies for
assessing response and coordination regarding
erosion and sedimentation management and
capacity Building

conclusion
‣ The principal reservoirs of Afghanistan are rapidly losing their
storage capacity and day by day exacerbated because of high rates
of sediment influx and accumulation.
‣ The factors that promote sedimentation in the reservoirs include
land use, steep drainage basin slopes and relief, and most
importantly, high rainfall magnitudes and frequencies and lack of o
maintenance due to prolong war.
‣ connecting reservoirs at high elevations with those at lower
elevations, results in an increased drainage area and available
water. As the upstream reservoirs fill with sediment, however, the
bottoms reach the outlet structures and sediment is bypassed into
the lower reservoirs, accelerating the sedimentation rates in these
impoundments.

‣ Reservoirs with small drainage areas loss
storage capacity at a faster rate than
reservoirs with larger basins, especially in
developed basins.
‣ In reservoirs with large basins
however,intense rainfall in a short period
can transport large amounts of sediment
into the reservoirs, rapidly depleting their
storage capacity.

‣ Efforts to significantly increase the overall
water resources by simply building more
dams over time , is proving to be
ineffective on a long-term basis.

Thank you for attention