Meteorology: Precipitation and Rain Gauges

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Questions and Answers

What is the term for the precipitation experienced on the d/s side of a mountain range?

Convective precipitation

Rain shadow (correct)

Orographic precipitation

Cyclonic precipitation

How do cyclones affect precipitation patterns?

They exclusively produce snowfall.

They cause precipitation only during warm fronts.

They lead to precipitation that can vary from drizzle to steady rain. (correct)

They are responsible for steady rain only.

Which type of rain gauge is designed to capture and record rainfall measurements continuously?

Scale type rain gauge

Simon type rain gauge

Non-recording type rain gauge

Recording type rain gauge (correct)

What process leads to the formation of clouds during convective precipitation?

Adiabatic cooling Signup and view all the answers

What type of precipitation tends to be intense but of short duration when caused by cold fronts?

Cyclonic precipitation Signup and view all the answers

Which atmospheric phenomenon is marked by a large mass of air circulating in a specific direction?

Cyclone Signup and view all the answers

What feature describes the area where heavy rains are recorded due to orographic effects?

Windward slope Signup and view all the answers

What is the primary use of point rainfall measurements obtained from rain gauges?

To compute mean areal rainfall Signup and view all the answers

What is the maximum capacity of the receiving bottle used for measuring rainfall?

100mm Signup and view all the answers

How often should observations be taken during heavy rainfall?

3 to 4 times a day Signup and view all the answers

What is the measuring accuracy of the graduated measuring cylinder?

0.1mm Signup and view all the answers

Which type of rain gauge is referred to as the standard recording rain gauge adopted in India?

Float type rain gauge Signup and view all the answers

What does the pen in a float type rain gauge record when the float rises?

A curve on the rain chart Signup and view all the answers

What happens when the float in the float type rain gauge reaches the top of the container?

The siphon drains the water Signup and view all the answers

How does the weighing type rain gauge measure rainfall?

By tracking the weight of water accumulation Signup and view all the answers

What kind of information does a recording type rain gauge provide?

The start and end of a rainfall event Signup and view all the answers

Which branch of hydrology focuses on the planning and design of projects for water control and use?

Engineering Hydrology Signup and view all the answers

Which process is NOT involved in the hydrologic cycle?

Inflation Signup and view all the answers

What is the primary energy source that activates the evaporation process in the hydrologic cycle?

Solar radiation Signup and view all the answers

Which type of hydrology studies the chemical characteristics of water?

Chemical Hydrology Signup and view all the answers

What term describes the continuous circulation of water within the Earth's hydrosphere?

Hydrologic Cycle Signup and view all the answers

Which aspect of hydrogeology is focused on the study of groundwater?

Ground Water Hydrology Signup and view all the answers

Which of the following processes involves the vaporization of water from its sources?

Evaporation Signup and view all the answers

Which branch of hydrology examines the interactions between organisms and the hydrological cycle?

Eco-hydrology Signup and view all the answers

What is the first step in determining the effective area of a raingauge station?

Draw perpendicular bisectors of each line. Signup and view all the answers

Which formula is used to compute the mean areal rainfall depth using Theissen Polygon Method?

$P̅ = ∑𝑛𝑖=1 𝑃𝑖 𝐴𝑖 / 𝐴$ Signup and view all the answers

In the Theissen Polygon Method, for which station was the enclosed area smallest?

D Signup and view all the answers

What is the measured rainfall for station C?

9.57 cm Signup and view all the answers

How much rain was measured at station B?

11.56 cm Signup and view all the answers

What is the total area of all enclosed polygons for the raingauge stations?

95.25 sq km Signup and view all the answers

What do the bisectors form around each raingauge station?

Polygons Signup and view all the answers

What is the mean areal rainfall computed from the given data?

10.56 cm Signup and view all the answers

What is the maximum length of overland flow typically observed?

150 m Signup and view all the answers

Which of the following best describes the term 'effective rainfall'?

Rainwater remaining after initial losses are satisfied Signup and view all the answers

What type of runoff occurs soon after the start of a rainfall event?

Direct runoff Signup and view all the answers

Which phenomenon describes the movement of standing water down the slope after rainfall?

Overland flow Signup and view all the answers

What must occur for runoff to take place after rainwater is introduced?

Rainwater must flow into a channel Signup and view all the answers

Which type of runoff occurs before reaching the main groundwater table?

Interflow Signup and view all the answers

What is the importance of maintaining the water level outside the ring during infiltration tests?

To ensure accurate measurement of infiltration rates Signup and view all the answers

In the context of runoff, what does 'indirect runoff' potentially refer to?

Runoff that originates from groundwater Signup and view all the answers

What does the variable 'm' represent in Weibul's equation for plotting position?

The rank number of the event after arranging in descending order Signup and view all the answers

How is the return period (T) calculated in relation to plotting position (p%)?

T = 1/p% Signup and view all the answers

What would the plotting position be for the highest rainfall of 50cm recorded over 50 years?

1.96% Signup and view all the answers

In the case of two highest rainfall events of 25cm in 1987 and 1995, what is the rank number for the year 1995?

2 Signup and view all the answers

Given a length of record (n) of 75 years and a rank number (m) of 1, what is the plotting position for 1987?

1.25% Signup and view all the answers

What is the calculated return period (T) for the rainfall depth of 25cm observed in 1987?

80 years Signup and view all the answers

What is the plotting position formula applied in the context of extreme rainfall events?

p% = m/(n + 1) x 100 Signup and view all the answers

Which of the following is a correct description of the Weibul's equation used for rainfall frequency?

It plots rainfall events based on historical data. Signup and view all the answers

Study Notes

Watershed Hydrology (SWC-201) Lecture Notes

Course: Watershed Hydrology (SWC-201)
Instructor: Dr. R. Suresh, Professor SWE
Department: Soil & Water Engineering
College: College of Agricultural Engineering
University: R.P.C.A.U., Pusa (Samastipur)-848 125

Lecture 1: Introduction

Hydrology: The science of water, its occurrence, distribution, circulation on and below the earth, and its interaction with earth materials.
Watershed: A land area in which all precipitation drains to the same point, a basin or catchment.
Importance of Hydrology: Understanding water production from catchments; relationship between surface and groundwater; flood forecasting and design of hydraulic structures; water supply design; crop planning.
Divisions of Hydrology: Engineering hydrology (design and operation of water projects), Applied hydrology (study of hydrological cycle, precipitation, runoff), Chemical hydrology (chemical characteristics of water), Eco-hydrology (interaction between organisms and the hydrological cycle), Hydrogeology (groundwater), Hydro-informatics (information technology in hydrology), Hydrometeorology (water-energy transfer), Isotope hydrology (origin and age of water).

Lecture 2: Watershed- Concepts and Laws

Watershed Components:
Boundary: Defines the size and shape of the watershed, typically ridges or elevated areas.
Stream Network: Interconnected stream system draining the watershed to the outlet. Drainage density is the ratio of total stream length to total area.
Watershed Soils/Land: Varied soil types and their characteristics affect water movement and availability.
Land Use System: Different land uses (agriculture, forests, etc.) influence the hydrological behavior of the watershed.

Lecture 3: Clouds and Precipitation

Clouds: The source of precipitation, including nimbostratus (continuous rain) and cumulonimbus (thunderstorms).
Precipitation: Moisture from clouds falling as rain, snow, hail, sleet impacting water resources and affecting various activities.
Forms of Precipitation: Liquid forms (rain, drizzle), solid forms (snow, sleet, hail).
Factors affecting precipitation: Evaporation, Condensation, Sublimation, Precipitation

Lecture 4: Rainfall Measurement

Rain Gauges: Used to measure rainfall, Non-recording (measuring rainfall at a particular interval) type and recording (continuous) type.
Non-recording: Simplest type, using a funnel and bottle to collect rainfall.
Recording: More complex types, automatically recording rainfall events.
Float: Water level rise causes a float to move, recording on a chart.
Weighing: An increasingly heavier float/lever system indicates rainfall.
Tipping bucket: Each 0.25 mm rainfall causes a bucket to tip, recorded mechanically or electronically.

Lecture 5: Mean Areal Rainfall

Computing Mean Areal Rainfall: Method used to determine average rainfall over a large area.
Arithmetic Average Method: Simple average of collected rainfall data at individual stations.
Thiessen Polygon Method: Area-weighted average using polygons around stations.
Isohyetal Method: Plotting isohyets (lines of equal rainfall), determining average precipitation in each area between the isohyets.

Lecture 6: Rainfall Analysis

Mass Curve: Accumulated rainfall over time.
Double Mass Curve: Used to check consistency of data, to identify abrupt changes in rainfall records.
Hyetograph: Rainfall intensity versus time, showing rainfall distribution over a period.

Lecture 7: Rainfall Abstractions and Initial Loss

Initial Loss: Water losses due to interception, evaporation, infiltration, and depression storage prior to runoff.
Interception: Precipitation intercepted by vegetation and then evaporated.
Depression Storage: Water stored in surface depressions that evaporates or infiltrates.
Infiltration: Water entering the soil.
Runoff coefficient: The proportion of rainfall that becomes runoff.

Lecture 8: Runoff and its Computation

Runoff: Excess water flowing over the land surface into channels, rivers or other watercourses.
Runoff Classification:
Direct Runoff: Runoff generated directly from rainfall.
Indirect Runoff: Runoff generated from groundwater or interflow.
Factors Affecting Runoff: Rainfall intensity, duration, distribution and direction, watershed characteristics (size, shape, slope, soil type, vegetation, and land use) as affecting factors.

Lecture 9: SCS method of Runoff Computation

Curve Number (CN): Represents the retention capacity of the soil.
Antecedent Moisture Conditions (AMC): Indicates the previous moisture level of the soil.
Soil hydrologic Groups: The classifications of the soil that determines the retention and infiltration properties.
Equation: (P-02.S)2 Q = (P+0.8S)
where P is rainfall , Q is Runoff, S is storage/ retention

Lecture 10: Cook's Method of Runoff Computation

Method: Four watershed characteristics: relief, infiltration rate, vegetation cover, and surface storage.
Numerical Values (W): Assigned to each characteristic based on its influence on runoff.
Runoff rate: Determined using the selected curve and ∑W value.
Equation: Qpeak = prfs

Lecture 11: Hydrograph

Hydrograph Definition: A graph plotting stream discharge against time, showing rise and fall of water.
Characteristics of a Hydrograph: Rising limb (increasing discharge), peak (maximum discharge), falling limb (decreasing discharge). Base flow (continuous, slow flow).
Factors affecting the hydrograph: Rainfall intensity, duration, watershed characteristics and time of the year.

Lecture 12: Unit Hydrograph

Unit Hydrograph Definition: A standardized hydrograph response to a unit depth of rainfall.
Assumptions of the Unit Hydrograph: Uniform distribution of rainfall, duration of rainfall, time and linearity.
Limitations: Not valid for all rainfall patterns or areas, not applicable for large areas or areas with temporal and spatial variation in intensity and duration of rainfall events.

Lecture 13: Unit Hydrograph for Different Durations

Superposition Method: Used when the duration of effective rainfall is a multiple of the basic UHG.
S-curve Method: Used when the duration of effective rainfall is not a multiple of the basic UHG.

Lecture 14: Synthetic Unit Hydrograph (SUHG)

Purpose: Estimate the streamflow response for un-gauged or ungaged watersheds.
Key Parameters: Basin lag (time between center of rainfall excess and peak of hydrograph), and standard duration of effective rainfall.
Computation procedure

Lecture 15: Stream Flow Measurement

Methods: Various techniques like staff gauge, chain/tape gauge, current meter, Pressure transmitter, crest stage indicator, and automatic stage recorder.

Lecture 16: Manning's Formula

Mannings Formula: Estimate flow velocity in open channels like rivers or natural streams. V = 1.49R^(2/3)S^(1/2)/n. Where V is the flow velocity, R is the hydraulic radius, S is the slope of the stream and n is Manning's roughness coefficient.
Factors affecting flow velocity: Hydraulic radius, slope and roughness (including vegetation).
Different types of channels: Including straight, irregular, rocky, weedy etc
Manning's roughness coefficient (n): Values for various channel conditions are provided in a table.

Lecture 17: Dilution Method

Purpose: To estimate stream discharge.
Principle: A known amount of tracer substance (e.g., salt) is added to the stream, and the concentration is measured downstream at a fixed rate.
Chemical Properties: Chemically conservative, easily measurable, soluble, non-toxic

Lecture 18: Stream- Discharge Relationship

Relationship: Plotted on log-log graph paper. The relationship is between discharge (Q) and stage (G).
Equation: Log Q = β log (G – a) + log C, where a, β, and C are constants determined from the data.
Procedure: Plot discharge versus stage.
Determination of constant "a": Determine the gauge height corresponding to zero discharge using the graph.

Lecture 19: Stream Flow and Reservoir Routing

Flood Routing: Determines the timing and magnitude of a flood wave at a point on a stream from known data at an upstream point.
Continuity Equation: dS/dt = I – O, where S is storage, I is inflow, and O is outflow.

Lecture 20: Routing Procedure

Muskingum Method: One of the method to compute the stream flow downstream of a specified point.
Calculation of Constants: The method involves calculating constants (Co, C1 and C2) based on the storage constant (K) and weighing factor (x).

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Description

Test your knowledge on precipitation concepts and rain gauge measurements in meteorology. This quiz covers various types of precipitation, the influence of cyclones, and the functionality of different rain gauges. Perfect for students studying atmospheric science and meteorology topics.