midterm

Question 1

is the transfer of water from the liquid to the vapor state

Answer 1

Evaporation

Question 2

is the process by which plants remove water from the soil and release it into the air as vapors.

Answer 2

Transpiration

Question 3

is the combined processes of losing water to the atmosphere from water surface, soil surface, and from plants.

Answer 3

Evapotranspiration

Question 4

Factors affecting the rate of Evaporation (6)

Answer 4

1. Vapor pressure at the water surface and above.
2. Air and Water Temperatures
3. Wind Speed
4. Atmospheric Pressure
5. Quality of Water
6. Size of Water Bodies

Question 5

The rate of evaporation is proportional to the difference between the saturation vapor pressure at the water temperature,

ew and the actual vapor pressure in the air, ea,

thus,
EL = c (ew – ea)

Answer 5

1. Vapor pressure at the water surface and above.

Question 6

with all factors remaining the same, the rate of evaporation increases with an increase in the water temperature.

Answer 6

Air and Water Temperatures

Question 7

With aids in removing the evaporated water vapor from the zone of evaporation and
consequently creates greater scope of evaporation. The rate of evaporation increases with the wind speed up to critical speed.

Answer 7

Wind Speed

Question 8

With all factors remaining the same, a decrease in barometric pressure increases evaporation.

Answer 8

Atmospheric Pressure

Question 9

When a solute is dissolved in water, the vapor pressure of the solution is lesser than that of
pure water and hence causes reduction on the rate of evaporation

Answer 9

Quality of Water

Question 10

Deep water bodies have more heat storage than shallow ones. A deep lake may store
radiation energy in summer and release it in winter causing less evaporation in summer and
more evaporation in winter.

Answer 10

Size of Water Bodies

Question 11

________ is very important in many hydrologic problems associated with planning and operation of reservoirs and irrigation systems. It is also important in areas where water is scarce. The exact measurement of evaporation is one of the most difficult tasks.

Answer 11

Determination of Evaporation

Question 12

Determination of Evaporation
It can be estimated using the
following methods: (3)

Answer 12

1. Using evaporimeter data
2. Empirical evaporation equations
3. Analytical methods

Question 13

_________ are water-containing pans which are exposed to the atmosphere and the loss of water by
evaporation is measured in them at regular intervals. Factors affecting the rate of evaporation are also
noted such as humidity, wind movement, air and water temperatures and precipitation.

Answer 13

Evaporimeters

Question 14

Types of Evaporimeters: (4)

Answer 14

1. Class A Evaporation Pan
2. ISI Standard Pan
3. Colorado Sunken Pan
4. US Geological Survey Floating Pan

Question 15

This consists of 1210 mm width and a depth of 255 mm. It is used by the U.S. Weather Bureau and is known as Class A Land Pan.
The depth of water is maintained below 18 cm and 20 cm. The pan is normally made of unpainted galvanized iron sheet. Monel metal is used where corrosion is problem. The pan is supported by wooden platform of 15 cm height above the ground to allow
free circulation of air below the pan.
Evaporation measurements are made by measuring the
depths of water with a hook gauge in a stilling well.

Answer 15

1. Class A Evaporation Pan

Question 16

This is known as modified Class A Pan. It consists of a pan 1220 mm in diameter with 255 mm of
depth. The pan is made of copper sheet of 0.90 mm thickness, tinned inside and painted white outside. A fixed-point gauge indicates the level of water. A calibrated cylindrical measure is used
to add or remove water, maintaining the water level in the pan to a fixed mark. The top of the pan is covered fully with a hexagonal wire netting on a galvanized iron to protect the water in the
pan from birds and to make the temperature more uniform during the day and night. The evaporation of this pan is found to be less by 14% compared to unscreened pan.

Answer 16

ISI Standard Pan

Question 17

This is a 920 mm square and 460 mm deep made up of unpainted galvanized iron sheet and buried into the ground within 100 mm at the top. The main advantage of this type is that radiation and aerodynamic characteristics are similar to a lake.
However, it has the following disadvantages:
a. Difficult to detect leaks
b. Extra care is needed to keep the surrounding area free from all grass, dust, etc.
c. Expensive to install

Answer 17

Colorado Sunken Pan

Question 18

A square pan with 900 mm side and 450 mm depth supported by drum floats in the middle of a raft is set afloat on a lake to simulate the characteristics of a large body of water. The water level
is kept constant leaving a rim of 75 mm. Diagonal baffles provided in the pan reduce the surging
in the pan due to wave action.

Answer 18

US Geological Survey Floating Pan

Question 19

Evaporation pans are not exact models of large reservoirs and have the following drawbacks:

Answer 19

1. They differ in the heat-storing capacity and heat transfer from the sides and bottom.
2. The height of the rim in an evaporation pan affects the wind action over the surface.
3. The heat-transfer characteristics of the pan material are different from that of the reservoir.

Question 20

Empirical Evaporation Equations

Answer 20

1. Meyer’s Formula
2. Rohwer’s Formula

Question 21

Analytical Method of Estimating Evaporation (3)

Answer 21

1. Water-Budget Method
2. Energy-Balance Method
3. Mass-Transfer Method

Question 22

Methods for Reduction of Evaporation Losses

Answer 22

1. Reduction of Surface Area
2. Mechanical Cover
3. Chemical Films

Question 23

The volume of water lost by evaporation is directly proportional to the surface area of the water
body, this reduction of surface area can reduce evaporation loss. Using deep reservoirs in place of wider ones can meet this method of reducing loss of water.

Answer 23

1. Reduction of Surface Area

Question 24

Permanent, temporary of floating roofs can be used to cover reservoirs, but this is only feasible for smaller water bodies.

Answer 24

Mechanical Cover

Question 25

this method consists of **applying a thin chemical film on the water surface to reduce evaporation.** This is **feasible for reservoirs of considerable size.**

Answer 25

Chemical Films

Question 26

is the **process by which water leaves the body of a living plant and reaches the atmosphere as vapor.** The water is taken up by the plant-root system and escape through the leaves.

Answer 26

Transpiration

Question 27

Factors Affecting Transpiration:

Answer 27

1. Atmospheric vapor pressure 2. Temperature 3. Wind 4. Light intensity 5. Characteristics of plants

Question 28

the **resulting evapotranspiration** when sufficient moisture is always available to completely meet the needs of vegetation covering the area. These **depends essentially on the climactic factors.**

Answer 28

Potential Evapotranspiration (PET)

Question 29

the real evapotranspiration occurring in a specific situation

Answer 29

Actual Evapotranspiration (AET)

Question 30

denotes loss by evapotranspiration.

Answer 30

Consumptive Use

Question 31

the **maximum quantity of water that the soil can retain** against the force of gravity.

Answer 31

Field Capacity

Question 32

the **moisture content of a soil at which the moisture is no longer available in sufficient quantity** to sustain the plants.

Answer 32

Permanent Wilting Point

Question 33

the difference between the field capacity and the permanent wilting point.

Answer 33

Available Water

Question 34

Measurement of Evapotranspiration

Answer 34

1. Lysimeter 2. Field Plot

Question 35

A **special water tank containing a block of soil and set in a field of growing plants.** The plants grown in the ________ are the same as in the surrounding field. **Evapotranspiration is estimated in terms of the amount of water required to maintain constant moisture conditions** within the tank measured wither volumetrically through an arrangement made in the lysimeter. _________ should be designed to accurately reproduce the soil condition, moisture content, type and size of the vegetable of the surrounding area. They should be buried so that the soil is the same level inside and outside the container.

Answer 35

1. Lysimeter

Question 36

In a **special plot all the elements of the water budget in a known interval of time** are measured and the evapotranspiration is determined as: Evapotranspiration = precipitation + irrigation input – runoff – increase in soil storage – groundwater loss

Answer 36

Field Plot

Question 37

refers to the **process of reducing the water volume for runoff.** This consists of the interception process and the depression storage. This abstraction represents the quantity of storage that must be satisfied first before run-off begins.

Answer 37

Initial loss

Question 38

is the **volume of water caught by the vegetation and the structures** and then subsequently evaporated.

Answer 38

Interception

Question 39

This is the **volume of water that fills up all the depressions when precipitation reaches the ground** before overland flow occurs. This is **lost through the process of filtration and evaporation.**

Answer 39

depression Storage

Question 40

This is the **movement of water through the soil surface** which plays an important role in the run-off process by **affecting the timing, distribution, and magnitude of the surface run-off.** It is also the **primary step in the natural groundwater recharge.**

Answer 40

Infiltration

Question 41

is the **maximum rate at which the ground can absorb water.**

Answer 41

Infiltration Capacity

Question 42

is a **device used to measure the rate of infiltration.** It consists of a cylinder driven into the ground and a buffer cylinder driven into the ground concentric with the cylinder. The cylinders are filled with water up to the same level and the change in water levels is observed for a time duration. The **purpose of the buffer cylinder is to ensure that the flow of water is truly vertical representing the infiltration**

Answer 42

Infiltrometer

Question 43

Factors affecting infiltration:

Answer 43

1. Type of Soil 2. Properties of Soil 3. Structure of Soil 4. Size of soil particle 5. Texture of soil 6. Condition of surface

Question 44

means the **draining or flooding off of precipitation from a catchment area** through a surface channel.

Answer 44

Run-off

Question 45

is the **excess precipitation** moving over the land surfaces to reach smaller channels.

Answer 45

Overland Flow

Question 46

a **flow travelling all the time over the surface as overland flow** and through the channels as open channel flow and reaching the catchment area.

Answer 46

Surface runoff

Question 47

is a **part of the precipitation that infiltrates and moves laterally through upper crusts of the soil** and returns to the surface at some location away from the point of entry into the soil. This is sometimes called as **through flow, storm seepage, subsurface flow, or quick return flow. ** ________ is classified as: 1. Prompt interflow – an interflow with the least lag 2. Delayed flow

Answer 47

Interflow

Question 48

is a part of run-off that **percolates deeper into the soil and reaching groundwater storage.**

Answer 48

Groundwater flow or Groundwater runoff

Question 49

Classification of Runoff:

Answer 49

1. Direct Runoff 2. Baseflow

Question 50

The **part of runoff that enters the stream immediately after the precipitation.** It includes surface runoff, prompt interflow, and precipitation on the channel surface. This is **sometimes called as direct storm runoff or storm runoff.**

Answer 50

1. Direct Runoff

Question 51

The **delayed flow that reaches the stream essentially as groundwater flow** including delayed interflow.

Answer 51

Baseflow

Question 52

the **entire area of a river basin** whose surface runoff (due to a storm) **drains into the river in the basin.** Also known as **drainage basin, or catchment area.**

Answer 52

Watershed

Question 53

Parts of Watershed

Answer 53

* Drainage Divide * Concentration point or Measuring point * Concentration time

Question 54

**the boundary line,** along a topographic ridge, separating the two adjacent watersheds.

Answer 54

Drainage Divide

Question 55

the **single point or location at which all surface drainage from a watershed comes together** or concentrates as outflow of the basin in the stream channel.

Answer 55

Concentration point or Measuring point

Question 56

the **time required** for the rain falling at the most distant point in a watershed **to reach the concentration point.**

Answer 56

Concentration time

Question 57

Physical Characteristics of a Watershed

Answer 57

* The **number** of streams * the **length** of streams * **stream density** – which is expressed as the number of streams per square kilometer area of the watershed. * **drainage density** – which is expressed as the total length of all stream channels per unit area of the watershed.

Question 58

Classification of Streams

Answer 58

1. Influent Streams and Effluent Streams 2. Intermittent and Perennial Streams

Question 59

when the **seepage from the stream feeds the groundwater resulting in the build up of water mound.** This happens when the ground water table is below the bed of the stream. **Such streams will dry up completely in rainless period** and are called **ephemeral streams.**

Answer 59

Influent Streams

Question 60

the **ground water feed the stream.** This happens when the ground water table is **above the bed of the stream.**

Answer 60

Effluent Streams

Question 61

when the ground water table lies above the stream during the wet season but drops below the bed during the dry season. **The stream flows during wet season due to surface runoff and groundwater contribution but becomes dry during dry seasons.**

Answer 61

Intermittent Streams

Question 62

when the **ground water table never drops below the bed of the stream** even in the most severe droughts and therefore **they flow throughout the year.**

Answer 62

Perennial Streams

Question 63

is that **balance of water,** which flows or **runs over the natural ground surface after losses** by evaporation, interception and infiltration.

Answer 63

Run-off

Question 64

the **net quantity of water available for storage,** after all loses, for the **purposes of water resource utilization and planning, like irrigation, water supply, etc. **

Answer 64

Yield of Catchment

Question 65

it is the **discharge in times of flooding of the catchment area,** i.e., when the intensity of rainfall is greatest and the condition of catchment regarding humidity is also favorable for an appreciable run-off.

Answer 65

Maximum Flood Discharge

Question 66

Run-off Estimation Methods:

Answer 66

1. Empirical Formulae, curves, and tables 2. Infiltration Method 3. Rational Method 4. Overland Flow Hydrograph 5. Unit Hydrograph Method

Question 67

**By deducting the infiltration loss,** i.e., the area under the infiltration curve, from the total precipitation or by the use of infiltration indices, which are already discussed. These methods are largely empirical and the derived values are applicable only when the rainfall characteristics and the initial soil moisture conditions are identical to those for which these are derived.

Answer 67

Infiltration Method

Question 68

a **rational approach** is to obtain the yield of a catchment by **assuming a suitable run-off coefficient.**

Answer 68

Rational Method

Question 69

**Overland flow occurs as a thin sheet of water over the ground surface** (soon after a storm starts), joins a stream channel, and then flows in the channel to the concentration point.

Answer 69

Overland Flow Hydrograph

Question 70

The **hydrograph of direct surface discharge measured at the outlet of drainage area, which produces a unit depth of direct runoff** (i.e., a Pnet of 1 cm over the entire area of the catchment) resulting from a unit storm of specified duration (called unit period) is called a unit hydrograph of that duration.

Answer 70

Unit Hydrograph Method -