midtems Flashcards
This type of precipitation happens in varying intensities. The areal extent of ____________________ is small in the range of less than 10km in diameter.
Convective Precipitation
It occurs when warm, moist air is drawn into a low-pressure cold front. The warm air rises as it is drawn into the low-pressure zone and is subjected to adiabatic cooling.
Cyclonic Precipitation
Precipitation which is caused by hills or mountain ranges deflecting the moisture-laden air masses upward, causing them to cool and precipitate their moisture.
Orographic Precipitation
This term is used generally when the water droplets are of size 0.5-6 mm.
Rain
It consists of ice crystals which is combined form of ice flakes. Initially these flakes
have density in the range of 0.06-0.15 g/cc (avg of 0.1 g/cc).
Snowfall
When water droplets are of size lesser than 0.5 mm. Its intensity should be less than 1 mm/hr. In this case, particles are of such range that they can be seen floating into the air.
Drizzle
When rain or drizzle comes in contact with cold ground at around 0°C, the water is
converted into ice coating termed as _______.
Glaze
It is frozen rain drop which is formed when rain falls through air at sub-atmospheric
temperature or sub-freezing temperature.
Sleet
consisting of balls or lumps of ice, called hailstones, that form during thunderstorms.
size > 8 mm
Hail
-Total rainfall over a specific area
- Rain gauges (in mm)
Rainfall Depth
-Length of time rainfall occurs
- Start to end of rainfall event
Rainfall Duration
rate of rainfall (mm/hr)
Rainfall Intensity
a graphical representation of rainfall intensity over time
HYETOGRAPH
refers to the quantification of precipitation at a specific
location using instruments like rain gauges. This method captures the amount of rain that falls over a fixed area, providing data that can be used for hydrological studies, weather forecasting,
and agricultural planning.
Point rainfall measurement
Example of Point Rainfall Measurement Instruments:
- Standard Rain Gauge
- Tipping Bucket Rain Gauge
- Weighing Rain Gauge
is an instrument used to measure the amount of precipitation, typically rain,
over a specific period. It usually consists of a cylindrical container with a funnel at the top that directs rainwater into a graduated measuring tube. The amount of water collected in the tube is then measured, usually in millimeters or inches, to determine the total rainfall.
rain gauge
Design: A simple cylindrical container with a funnel leading to a graduated measuring tube.
Usage: Measures the total rainfall over a period. The user manually checks and records the measurement.
Standard Rain Gauge (Non-Recording Rain Gauge)
Design: Contains a small bucket that tips and empties when it fills with a predetermined amount of water (often 0.2 mm or 0.01 inch). Each tip is recorded electronically.
Usage: Provides continuous, real-time measurements of rainfall, making it useful for automatic weather stations.
Advantages: Records both the amount and intensity of rainfall.
Tipping Bucket Rain Gauge
Design: Collects rain in a container placed on a scale. The weight of the water is measured and converted into a depth of rainfall.
Usage: Used in environments where snow or ice might accumulate, as it can weigh precipitation
in all forms.
Advantages: Highly accurate and can measure all types of precipitation (rain, snow, sleet).
Weighing Rain Gauge
Design: Uses laser or infrared beams to detect raindrops as they pass through a sensing area.
Usage: Commonly used in automated weather stations and aviation, where precise, real-time data is essential.
Advantages: Can measure the size and velocity of raindrops, which helps in calculating rainfall intensity.
Optical Rain Gauge
Design: Measures the sound of raindrops hitting a surface, typically used underwater to detect rainfall on the water’s surface.
Usage: Used in marine environments to monitor rainfall over oceans and large bodies of water.
Advantages: Can measure rain over a large area without direct contact.
Acoustic Rain Gauge
Design: Rainwater is collected in a large container with a float inside. The rise of the float
indicates the amount of rainfall, which is then recorded.
Usage: Used in hydrological studies, particularly in areas prone to heavy rainfall.
Advantages: Can handle large volumes of water, making it suitable for areas with intense
rainfall.
Float-Type Rain Gauge
refers to the amount of rainfall measured at a specific location, typically using a rain gauge.
Point rainfall
This method involves taking the simple average of rainfall measurements from multiple
points within the area of interest.
Arithmetic Average
This method assigns weights to each rain gauge based on the area it represent
Thiessen Polygon Method
This method involves drawing contour lines (isohyets) of equal rainfall on a map. The area between these lines is then used to calculate the average rainfall.
Isohyetal Method
Converting point rainfall to aerial rainfall is crucial for designing and managing water
resources projects, such as dams, drainage systems, and flood control measures.
Areal Reduction Factors (ARF)
Is a graphical method used to check the consistency of precipitation data over
time.
DOUBLE MASS ANALYSIS
is the process where water on the ground surface enters the soil. It happens naturally when rain, irrigation, or any water source moves through the soil, filling gaps and spaces between particles.
Infiltration
Essential for sustaining water supplies and ecosystems, especially during dry periods.
Groundwater Recharge
Helps prevent flooding and erosion by reducing the volume of water that flows over land.
Reduction of Surface Runoff
Improves water quality by filtering contaminants as water moves through the soil.
Pollutant Filtration
Factors affecting infiltration
Precipitation Level, Soil Characteristics, Vegetative Cover, Slope of the Land, Soil Saturation, Evapotranspiration Level, Human Activities
can either increase or decrease infiltration.
Vegetative cover
refer to the assessment of how much water seeps into the soil from precipitation, irrigation, or other sources.
Infiltration Measurements
is a simple instrument that is used to determine the rate of infiltration of water into the soil. The rate of infiltration is determined as the amount of water per surface area and time unit, that penetrates the soil.
Double Ring Infiltrometer
a ring is driven into the ground and water is either continuously supplied or provided at a falling head condition.
Single Ring Infiltrometer
which apply water over a circular portion of the soil surface and measure the flow rate of water drawn into the soil, are widely used instruments for measuring the hydraulic conductivity of soil in the field.
Tension Infiltrometers
The ______________ is a significant empirical framework in hydrology, developed by Robert E. Horton in the early 1930s. It describes how the infiltration capacity of soil decreases over time during a rainfall event.
Horton Model
the model is not directly linked to measurable physical properties of the soil
Parameter Measurement
best suited for short-duration, high-intensity rainfall events and may not perform well under continuous or prolonged rainfall conditions
Limited Applicability
provides a reliable method for estimating how quickly water can infiltrate into soil
Estimation of Infiltration Rates
model captures the decrease in infiltration capacity over time
Dynamic Modeling
aids in designing effective stormwater management systems
Applications in Urban Planning
Horton’s work has laid the groundwork for subsequent advancements
Foundation for Further Research
The __________________________ is used to describe water infiltration into soils. It was developed by J.R. Philip in 1957 and is commonly applied to model unsteady infiltration of water into soil.
Philip’s Equation (or Philip’s infiltration equation)
The ______________________is an approximate model utilizing Darcy’s law. The model is developed with the assumption that water is ponded on the ground surface. Consider a vertical column of soil of unit horizontal cross-sectional area and let a control volume be defined around the wet soil between the surface and depth L.
Green-Ampt model
The Green-Ampt model was developed by ____________ and ______________ in the early 1900s, estimates downward infiltration when water ponds on the soil surface. It builds on earlier research in soil physics, particularly Edgar Buckingham’s work on unsaturated soil flow.
Heber Green & G.A. Ampt
helps explain why infiltration rates decrease over time, as the hydraulic gradient driving infiltration diminishes. Despite its assumptions, it remains a valuable tool for understanding and predicting infiltration dynamics.
The Green-Ampt model
___________ in hydrology refers to the period during which water accumulates on the surface of the ground or in depressions, such as ponds or fields, before it begins to infiltrate into the soil or runoff into nearby water bodies. It is a key factor in surface water dynamics, especially in areas with low infiltration rates or impervious surfaces, such as urban settings.
Ponding time
is the time interval between the onset of rainfall and when water starts to pool or accumulate on the ground surface due to the ground’s inability to absorb all the rainfall immediately.
Ponding time
