(SEM V) THEORY EXAMINATION 2022-23 ENGINEERING HYDROLOGY

SECTION A – Short Answer Type Questions (2 Marks each)

(a) Write the Water Budget Equation.

The water budget equation expresses the balance between the inflow, outflow, and storage of water in a hydrological system.

P=R+E+ΔSP = R + E + \Delta SP=R+E+ΔS

Where:

P = Precipitation (input)             R = Runoff (surface flow)              E = Evapotranspiration (loss)

ΔS = Change in storage (groundwater + surface water)

Importance:
This equation helps in estimating water availability, designing reservoirs, and understanding drought or flood conditions in a catchment area.

(b) Define Actual Evapotranspiration (AET).

Actual Evapotranspiration (AET) is the real rate of water loss from soil and vegetation to the atmosphere under existing conditions of moisture availability.
It differs from potential evapotranspiration (PET), which is the maximum possible loss if water is not limiting.

Formula (conceptual):

AET=f(P,PET)AET = f(P, PET)AET=f(P,PET)                         where AET is always ≤ PET.

Importance:

Used in irrigation scheduling, crop water requirement studies, and hydrological balance computation.

SECTION B – Long Answer Type Questions (10 Marks each)

(a) Explain the Different Forms of Precipitation.

Precipitation refers to all forms of water—liquid or solid—that fall from clouds and reach the ground.

Major forms:

Rain: Liquid water droplets larger than 0.5 mm; most common in tropical regions.

Drizzle: Small droplets (< 0.5 mm); common in foggy or coastal climates.

Snow: Ice crystals formed when temperature < 0°C; accumulates in polar or high-altitude regions.

Sleet: Mixture of rain and partially frozen pellets; occurs when warm air overlays cold air.

Hail: Hard balls of ice formed in cumulonimbus clouds during thunderstorms.

Tropical Cyclone (Schematic Section):

Structure: eye → eyewall → spiral rain bands.

Characterized by low pressure, high velocity winds, and torrential rainfall.

Engineering Relevance: Understanding precipitation types helps design drainage, flood control, and irrigation systems.

(b) Explain Double Mass Curve of Rainfall and its Use.

The Double Mass Curve (DMC) is a graphical method used to check and correct inconsistencies in rainfall records of a station.

Principle:
If the rainfall data of a station and the average rainfall of surrounding stations are consistent, their cumulative plots form a straight line. Any deviation indicates data inconsistency.

Steps:

Plot cumulative rainfall of the test station (Y-axis) vs cumulative mean rainfall of nearby stations (X-axis).

Identify changes in slope indicating inconsistency.

Determine correction factor as the ratio of old and new slopes.

Apply this correction to adjust the inconsistent data.

Applications:

Used for data quality control in hydrological studies.

Ensures reliable flood and drought analysis.

SECTION C – Very Long Answer Type Questions (10 Marks each)

(a) Explain Hydrograph and Its Components.

A hydrograph is a graphical representation showing the variation of discharge (flow rate) of a stream or river with time at a particular point.

Components of a Hydrograph:

Rising Limb: Represents the increase in discharge due to rainfall.

Crest Segment: Peak flow portion; indicates maximum discharge.

Recession Limb (Falling Limb): Decrease in discharge after rainfall stops.

Base Flow: Normal flow contributed by groundwater.

Lag Time: Time between rainfall peak and discharge peak.

Unit Hydrograph Concept:
A unit hydrograph represents direct runoff resulting from 1 cm of effective rainfall distributed uniformly over the catchment for a specified duration (e.g., 1-hr, 6-hr, 24-hr).
It helps in flood estimation, runoff prediction, and design of drainage structures.

(b) Differentiate between Open Wells and Tube Wells and Explain Their Construction.

Construction Method:

Site Selection: Based on groundwater survey and soil analysis.

Drilling/Boring: For tube wells using rotary or percussion methods.

Casing & Screen: Installed to prevent collapse and allow water entry.

Gravel Packing: To filter sediments.

Pumping Test: To determine yield and drawdown.

Significance:
Tube wells are widely used for irrigation, domestic water supply, and industrial uses due to their efficiency and reliability.