REVISION KNEC QUESTIONS MODULE 3
1. Define the term landslide. (2 marks)
- A collapse of a mass of earth or rock from a mountain or cliff.
2. Describe any four types of land slides. (8 marks)
Landslide movements are interpreted from the geomorphic expression of the landslide
deposit and source area, and are categorized as falls, topples, spreads, slides, or flows.
- Falls are masses of soil or rock that dislodge from steep slopes and free-fall,
bounce, or roll downslope.
- Topples move by the forward pivoting of a mass around an axis below the
displaced mass.
- Lateral spreads, commonly induced by liquefaction of material in an earthquake,
move by horizontal extension and shear or tensile fractures.
- Slides displace masses of material along one or more discrete planes. In
rotational sliding the slide plane is curved and the mass rotates backwards around
an axis parallel to the slope; in translational sliding the failure surface is more or
less planar and the mass moves parallel to the ground surface
- Flows mobilize as a deforming, viscous mass without a discrete failure plane.
3. Outline any five preventive measures of land slides. (10 marks)
- Slope Vegetation
One of the quickest and easiest ways to prevent a landslide on a slope is to
vegetate it.
- Retaining Walls
A solid, well-designed retaining should be made of sturdy materials such as
masonry, brick, stone or steel. Drainage materials behind the wall help increase
the stability of the wall.
- Diverting Debri Pathways
1
, Building pathways to divert debris is another option to prevent landslides on your
property.
- Temporary Prevention
For temporary landslide prevention, sandbags can be used to divert water from
uncontrolled spilling just as retaining walls or diverted pathways do. Another
method is to protect unstable areas with plastic sheeting, especially in areas
without vegetation because of recent fires.
4. Define the following bench terracing terminology. (8 marks)
i) Vertical interval
- Terrace spacing or the vertical distance between two successive bench terraces
ii) Horizontal interval
- It is the horizontal spacing between terraces. The distance between a point on one
terraces to a similar point on the next terrace.
iii) Maximum terrace length
- Horizontal distance from beginning to the end of a terrace. It is limited by the size
and shape of the field but a maximum of 100 m is recommended in one draining
direction although may be longer for ASAL areas.
iv) Terrace gradient
- Ratio of vertical interval to horizontal interval.
5. Given that the slope of a land is 10%, soil erodibility factor is 2, and rainfall erosivity
is 4, determine the vertical and horizontal interval of the terrace. (6 marks)
V.I= (S/a +b) 0.3 meters
Where a = the rainfall factor which varies depending on rainfall intensity amount
sequence and variability
b=soil erodibility
V.I. = (10/2+4)0.3 = 0.5
6. Define the following terms used in irrigation. (4 marks)
i) Field capacity
- Field Capacity is the amount of soil moisture or water content held in the soil
after excess water has drained away and the rate of downward movement has
decreased.
ii) Consumptive use
- Crop consumptive water use is the amount of water transpired during plant
growth plus what evaporates from the soil surface and foliage in the crop area.
7. A trapezoidal channel has the following characteristics;
- Manning’s roughness coefficient 0.04
- Depth of flow 4 meters
- Bed slope 0.5%
- Bottom width 4 meters
- Side slope inclination 450
Determine:
i) The discharge through the channel
ii) Whether the flow is turbulent or not
Reynolds number Re; Re = ρ u L / μ
2
, where
Re = Reynolds Number (non-dimensional)
ρ = density (kg/m3, lbm/ft3 )
u = velocity based on the actual cross section area of the duct or pipe (m/s, ft/s)
μ = dynamic viscosity (Ns/m2, lbm/s ft)
L = characteristic length (m, ft)
laminar - when Re < 2300
transient - when 2300 < Re < 4000
turbulent - when Re > 4000
Density of water = 1000Kg/m3
Dynamic viscosity of water = 8.90 × 10−4 Pa.
8. Outline THREE basic objectives of a water supply system. (6 marks)
- Supply wholesome and safe water to consumers
- To supply water in sufficient quantities
- To supply water at convenient points and timings
- To supply water at reasonable cost to users
- To encourage household and personal cleanliness of users
9. Describe the following methods of treating domestic water (6 marks)
i) Plain sedimentation
- Sedimentation is a simple, physical pre-treatment of water prior to application of
other purification treatments such as filtration and disinfection. It removes
undesirable small particulate suspended matter (sand, silt and clay) and some
biological contaminants from water under the influence of gravity. The longer the
water is held undisturbed, the more the suspended solids and pathogens will settle
to the bottom of the container. Adding coagulants can accelerate the sedimentation
process. Three common chemicals used for this purpose are aluminium sulphate,
polyaluminium chloride (also known as PAC or liquid alum) and ferric sulphate.
ii) Coagulation
- The coagulation process involves the addition of the chemical (e.g. alum) and then
a rapid mixing to dissolve the chemical and distribute it evenly throughout the
water. Alum produces positive charges to neutralize the negative charges on the
particles. Then the particles can stick together, forming larger particles which are
more easily removed.
iii) Filtration
- Water flows through a filter designed to remove particles in the water. The filters
are made of layers of sand and gravel, and in some cases, crushed anthracite.
Filtration collects the suspended impurities in water and enhances the
effectiveness of disinfection. The filters are routinely cleaned by backwashing.
iv) Disinfection
- Water is disinfected before it enters the distribution system to ensure that any
disease-causing bacteria, viruses, and parasites are destroyed. Chlorine is used
3
, because it is a very effective disinfectant, and residual concentrations can be
maintained to guard against possible biological contamination in the water
distribution system.
10. State the functions of a reservoir in a water supply system. (4 marks)
- storage,
- water conservation,
- flood control,
- water treatment
- Water for emergency supply like fire fighting
11. State;
i) Two effects of excess water in agricultural soil
I. The field will get water logged and the crop cannot get sufficient water and air, as
good aeration and warmth in the root zone are essential for proper plant growth.
II. Bacteria that change organic matter into plant foods cannot get necessary air and
warm temperature in the soil.
III. Desirable chemical reactions cannot take place and nutrient availability is not easily to
the plants.
IV. Proper root development and absorption of nutrients is not accelerated.
V. Seed germination is affected due to poor aeration and warm temperature.
VI. Plants affected by diseases and pest attack.
VII. Many toxic salts affecting water absorption by roots and causes damage to crops.
VIII. Agricultural operation viz. inter cultivation cannot be carried out properly.
ii) Two indicators of poorly drained soils (4 marks)
- In clay soils a pan will look a patchy grey/blue colour.
- Surface water, ponding and flooding.
- Yellow leaves on plants caused by a lack of nitrogen and oxygen.
- Machinery tracks.
- The soil particles pack together into clods.
- Mosses and other weeds.
12. Describe the following water drainage systems (16 marks)
i) Open ditch
Ditches can be of any shape or size and they can take large volumes of water. These
drains do use up land and do need looking after. Excessive weeds should be cleared so
they continue to work properly.
At shallow gradients, ditches should have smooth beds for unrestricted water flow.
Ditches must have a sufficient fall to allow free flowing water, but not so steep that
scouring or undercutting to the bottom and sides of the channel occurs. Gradients
between 1:15 and 1:40 will work effectively. If steeper ditches are unavoidable, try to
include bends and level areas to reduce water flow speed. Short steep sections may be
piped to avoid erosion of the ditch.
ii) Random ditch
The random ditch pattern is adapted to slowly permeable soils having depression
areas that are too large to be eliminated by land smoothing or grading. Field ditches
4
1. Define the term landslide. (2 marks)
- A collapse of a mass of earth or rock from a mountain or cliff.
2. Describe any four types of land slides. (8 marks)
Landslide movements are interpreted from the geomorphic expression of the landslide
deposit and source area, and are categorized as falls, topples, spreads, slides, or flows.
- Falls are masses of soil or rock that dislodge from steep slopes and free-fall,
bounce, or roll downslope.
- Topples move by the forward pivoting of a mass around an axis below the
displaced mass.
- Lateral spreads, commonly induced by liquefaction of material in an earthquake,
move by horizontal extension and shear or tensile fractures.
- Slides displace masses of material along one or more discrete planes. In
rotational sliding the slide plane is curved and the mass rotates backwards around
an axis parallel to the slope; in translational sliding the failure surface is more or
less planar and the mass moves parallel to the ground surface
- Flows mobilize as a deforming, viscous mass without a discrete failure plane.
3. Outline any five preventive measures of land slides. (10 marks)
- Slope Vegetation
One of the quickest and easiest ways to prevent a landslide on a slope is to
vegetate it.
- Retaining Walls
A solid, well-designed retaining should be made of sturdy materials such as
masonry, brick, stone or steel. Drainage materials behind the wall help increase
the stability of the wall.
- Diverting Debri Pathways
1
, Building pathways to divert debris is another option to prevent landslides on your
property.
- Temporary Prevention
For temporary landslide prevention, sandbags can be used to divert water from
uncontrolled spilling just as retaining walls or diverted pathways do. Another
method is to protect unstable areas with plastic sheeting, especially in areas
without vegetation because of recent fires.
4. Define the following bench terracing terminology. (8 marks)
i) Vertical interval
- Terrace spacing or the vertical distance between two successive bench terraces
ii) Horizontal interval
- It is the horizontal spacing between terraces. The distance between a point on one
terraces to a similar point on the next terrace.
iii) Maximum terrace length
- Horizontal distance from beginning to the end of a terrace. It is limited by the size
and shape of the field but a maximum of 100 m is recommended in one draining
direction although may be longer for ASAL areas.
iv) Terrace gradient
- Ratio of vertical interval to horizontal interval.
5. Given that the slope of a land is 10%, soil erodibility factor is 2, and rainfall erosivity
is 4, determine the vertical and horizontal interval of the terrace. (6 marks)
V.I= (S/a +b) 0.3 meters
Where a = the rainfall factor which varies depending on rainfall intensity amount
sequence and variability
b=soil erodibility
V.I. = (10/2+4)0.3 = 0.5
6. Define the following terms used in irrigation. (4 marks)
i) Field capacity
- Field Capacity is the amount of soil moisture or water content held in the soil
after excess water has drained away and the rate of downward movement has
decreased.
ii) Consumptive use
- Crop consumptive water use is the amount of water transpired during plant
growth plus what evaporates from the soil surface and foliage in the crop area.
7. A trapezoidal channel has the following characteristics;
- Manning’s roughness coefficient 0.04
- Depth of flow 4 meters
- Bed slope 0.5%
- Bottom width 4 meters
- Side slope inclination 450
Determine:
i) The discharge through the channel
ii) Whether the flow is turbulent or not
Reynolds number Re; Re = ρ u L / μ
2
, where
Re = Reynolds Number (non-dimensional)
ρ = density (kg/m3, lbm/ft3 )
u = velocity based on the actual cross section area of the duct or pipe (m/s, ft/s)
μ = dynamic viscosity (Ns/m2, lbm/s ft)
L = characteristic length (m, ft)
laminar - when Re < 2300
transient - when 2300 < Re < 4000
turbulent - when Re > 4000
Density of water = 1000Kg/m3
Dynamic viscosity of water = 8.90 × 10−4 Pa.
8. Outline THREE basic objectives of a water supply system. (6 marks)
- Supply wholesome and safe water to consumers
- To supply water in sufficient quantities
- To supply water at convenient points and timings
- To supply water at reasonable cost to users
- To encourage household and personal cleanliness of users
9. Describe the following methods of treating domestic water (6 marks)
i) Plain sedimentation
- Sedimentation is a simple, physical pre-treatment of water prior to application of
other purification treatments such as filtration and disinfection. It removes
undesirable small particulate suspended matter (sand, silt and clay) and some
biological contaminants from water under the influence of gravity. The longer the
water is held undisturbed, the more the suspended solids and pathogens will settle
to the bottom of the container. Adding coagulants can accelerate the sedimentation
process. Three common chemicals used for this purpose are aluminium sulphate,
polyaluminium chloride (also known as PAC or liquid alum) and ferric sulphate.
ii) Coagulation
- The coagulation process involves the addition of the chemical (e.g. alum) and then
a rapid mixing to dissolve the chemical and distribute it evenly throughout the
water. Alum produces positive charges to neutralize the negative charges on the
particles. Then the particles can stick together, forming larger particles which are
more easily removed.
iii) Filtration
- Water flows through a filter designed to remove particles in the water. The filters
are made of layers of sand and gravel, and in some cases, crushed anthracite.
Filtration collects the suspended impurities in water and enhances the
effectiveness of disinfection. The filters are routinely cleaned by backwashing.
iv) Disinfection
- Water is disinfected before it enters the distribution system to ensure that any
disease-causing bacteria, viruses, and parasites are destroyed. Chlorine is used
3
, because it is a very effective disinfectant, and residual concentrations can be
maintained to guard against possible biological contamination in the water
distribution system.
10. State the functions of a reservoir in a water supply system. (4 marks)
- storage,
- water conservation,
- flood control,
- water treatment
- Water for emergency supply like fire fighting
11. State;
i) Two effects of excess water in agricultural soil
I. The field will get water logged and the crop cannot get sufficient water and air, as
good aeration and warmth in the root zone are essential for proper plant growth.
II. Bacteria that change organic matter into plant foods cannot get necessary air and
warm temperature in the soil.
III. Desirable chemical reactions cannot take place and nutrient availability is not easily to
the plants.
IV. Proper root development and absorption of nutrients is not accelerated.
V. Seed germination is affected due to poor aeration and warm temperature.
VI. Plants affected by diseases and pest attack.
VII. Many toxic salts affecting water absorption by roots and causes damage to crops.
VIII. Agricultural operation viz. inter cultivation cannot be carried out properly.
ii) Two indicators of poorly drained soils (4 marks)
- In clay soils a pan will look a patchy grey/blue colour.
- Surface water, ponding and flooding.
- Yellow leaves on plants caused by a lack of nitrogen and oxygen.
- Machinery tracks.
- The soil particles pack together into clods.
- Mosses and other weeds.
12. Describe the following water drainage systems (16 marks)
i) Open ditch
Ditches can be of any shape or size and they can take large volumes of water. These
drains do use up land and do need looking after. Excessive weeds should be cleared so
they continue to work properly.
At shallow gradients, ditches should have smooth beds for unrestricted water flow.
Ditches must have a sufficient fall to allow free flowing water, but not so steep that
scouring or undercutting to the bottom and sides of the channel occurs. Gradients
between 1:15 and 1:40 will work effectively. If steeper ditches are unavoidable, try to
include bends and level areas to reduce water flow speed. Short steep sections may be
piped to avoid erosion of the ditch.
ii) Random ditch
The random ditch pattern is adapted to slowly permeable soils having depression
areas that are too large to be eliminated by land smoothing or grading. Field ditches
4
