Hydrology: Components of Stream Flow

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Questions and Answers

What is a drainage basin?

The location where all water in a catchment area evaporates

The total length of all streams in a given area

An area where surface runoff drains into a river (correct)

The area separated by topographic ridges that collects rainfall

What does the term 'drainage divide' refer to?

The point where water exits a river basin

The area where water from rainfall collects

The line along a topographic ridge separating two drainage basins (correct)

The average slope of a drainage basin

What does stream density indicate in a drainage basin?

The rate at which rainwater evaporates

The total volume of water in streams per area

The number of streams per square kilometer (correct)

The average depth of the streams

How is drainage density defined?

As the total length of all stream channels per unit area Signup and view all the answers

What does a high value of drainage density suggest about a basin?

Well-developed network with torrential runoff Signup and view all the answers

What is concentration time in the context of a drainage area?

The duration for rainfall to flow from the furthest point to the outlet Signup and view all the answers

What characterizes a low value of drainage density?

High permeability of the terrain and moderate runoff Signup and view all the answers

What does Horton’s method of determining slope involve?

Dividing the area into square grids and counting contours crossed Signup and view all the answers

What is the calculated value of the form factor, $F_f$?

0.502 Signup and view all the answers

What does the compactness coefficient, $C_c$, represent in terms of stream characteristics?

The ratio of perimeter to the product of radius and pi Signup and view all the answers

Which type of streams are predominantly nourished by groundwater?

Effluent streams Signup and view all the answers

How does the intensity of storms affect runoff according to the content?

Low intensity storms decrease runoff by increasing groundwater storage Signup and view all the answers

What is the calculated value of the circularity ratio, $C_r$?

0.358 Signup and view all the answers

What factor is NOT mentioned as influencing the runoff from a drainage basin?

Soil moisture content Signup and view all the answers

According to the content, what occurs when a succession of storms happens?

Runoff increases due to initial soil wetness Signup and view all the answers

What is the elongation ratio, $E_r$, calculated from the given data?

0.8 Signup and view all the answers

What is the relationship between drainage basin shape and flood intensity?

Fan-shaped catchments produce greater flood intensity. Signup and view all the answers

Which coefficient is dependent solely on the slope of the catchment?

Compactness coefficient Signup and view all the answers

What does the elongation ratio (Er) represent?

The diameter of a circle with the same area as the basin to its maximum length Signup and view all the answers

What is the range of values for the circularity ratio (Cr)?

0.2 to 0.8 Signup and view all the answers

Which equation represents the slope in the vertical direction (Sv)?

S = (Nc - C.I.) / ΣY Signup and view all the answers

For the example given, the mean slope of the basin was calculated to be approximately what value?

0.0461 m/m Signup and view all the answers

How is the mean slope (S) calculated from vertical and horizontal slopes?

S = (Sv + Sx) / 2 Signup and view all the answers

Which can be determined using the basin's area, perimeter, and length?

Form factor, compactness coefficient, elongation ratio, and circularity ratio Signup and view all the answers

Which factor influences greater runoff in steep rocky catchments?

Less vegetation Signup and view all the answers

What effect does thick vegetation have on water runoff?

Reduces runoff Signup and view all the answers

What is the significance of the windward side of mountains in relation to runoff?

Produces more runoff Signup and view all the answers

How does valley storage affect flood magnitude?

Reduces flood magnitude Signup and view all the answers

Which method is NOT a valid runoff estimation technique?

Vegetation density analysis Signup and view all the answers

What determines maximum flood discharge?

Humidity conditions and rainfall intensity Signup and view all the answers

What does the term 'yield of a catchment' refer to?

The net quantity of water available for storage Signup and view all the answers

Which empirical equation form produces an exponential curve?

R = aP^n Signup and view all the answers

What is one of the assumptions of the unit hydrograph method?

The unit hydrograph reflects all the physical characteristics of the basin. Signup and view all the answers

What does the variable 'C' represent in Chezy's equation?

Chezy's constant Signup and view all the answers

How is the hydraulic mean radius 'R' calculated?

R = A / P Signup and view all the answers

How is time of concentration calculated using Kirpich's formula?

$t_c = 0.02L^{0.8}S^{-0.4}$ Signup and view all the answers

What is the primary purpose of stream gauging?

To determine the runoff from a catchment. Signup and view all the answers

What is the purpose of using the slope-area method?

To estimate peak floods where no gauging station exists Signup and view all the answers

What does the equation $Q = CLH^{3/2}$ represent?

Stream discharge calculation through a flume. Signup and view all the answers

Which of the following variables represents the difference in water levels in the slope-area method?

Δh Signup and view all the answers

In the contracted area method, what does the term 'A1' signify?

Area of the most contracted section Signup and view all the answers

What unit is used to express the intensity of rainfall in the example given?

Centimeters per hour Signup and view all the answers

What does the coefficient of a weir depend on?

The design and shape of the weir. Signup and view all the answers

What does the variable 'S' represent in the slope-area method?

Water surface slope Signup and view all the answers

Which method involves introducing a chemical to determine discharge?

Salt-concentration method Signup and view all the answers

Which land cover type has the highest coefficient in the example provided?

Forest Signup and view all the answers

What role does 'n' play in the Manning's equation for calculating flow?

It is the coefficient of roughness Signup and view all the answers

What is the significance of using a uniform intensity of net rainfall in unit hydrograph theory?

It allows for a consistent base period across different hydrologic conditions. Signup and view all the answers

Study Notes

Components of Stream Flow

Runoff occurs when a portion of rainfall infiltrates into the ground, evaporates, or flows over the land surface as overland flow.
Infiltration can cause water to move laterally (interflow) or to seep deeper into the ground (groundwater flow).
Overland flow and interflow combine to create direct runoff, while groundwater flow is called base flow.
Depression storage refers to water held in puddles, pits, and small ponds during overland flow.
Surface detention is the volume of water in overland flow that hasn't reached the stream yet.
Bank storage is runoff absorbed by permeable stream banks.
Direct surface flow can be calculated for large areas using unit hydrographs, and for small areas using overland flow analysis.

Catchment Characteristics

A drainage basin is an area where runoff flows into a river.
Drainage divides are boundaries separating adjacent basins.
The point where water flows out of a basin is the concentration point.
Concentration time is the time it takes for water from the most distant part of a basin to reach the concentration point.
Stream density is the number of streams per square kilometer.
Drainage density is the total length of stream channels per unit area, indicating drainage efficiency.
Higher drainage density indicates more torrential runoff, while lower density suggests less.
Form factor (A/L) and compactness coefficient (P/√A) describe basin shape.
Basin shape categories are "fan-shaped" and "fern-shaped".

Classification of Streams

Influent streams are those where groundwater feeds the stream, often found in arid regions (groundwater is higher than the stream).
Effluent streams are those where the stream feeds groundwater (groundwater is lower than the stream).
Intermittent streams flow only during periods of rainfall (or snowmelt).
Perennial streams constantly flow year-round since they're fed by groundwater.

Factors Affecting Runoff

Storm characteristics (intensity, duration, area), meteorological characteristics (temperature, humidity, precipitation), and basin characteristics (size, shape, slope, geology) are key factors.
Large storms and areas generate greater runoff, while less intense storms and smaller areas produce less.
High humidity reduces evaporation, while snowpack and frozen ground increase runoff.
Steep, rocky regions with less vegetation lead to more runoff than flatter, vegetated areas.
Upstream reservoirs, lakes, and tanks can moderate peak flows.

Estimation of Runoff

Runoff is the portion of precipitation that flows over the land surface.
Empirical formulas, infiltration methods, rational methods, overland flow hydrographs, and unit hydrographs estimate runoff.
The empirical formulas use plots of precipitation (P) vs. runoff (R) data.
The rational method uses a runoff coefficient (C) to estimate peak runoff (Q) by Q = CIA, where C is the runoff coefficient (determined from type of catchment), I the rainfall intensity, and A the drainage area.
The unit hydrograph method uses a graph showing the relationship between rainfall intensity and runoff over time.

Stream Gauging

Stream gauging measures stream discharge at a gauging station.
Methods include using weirs or flumes, slope-area method, contracted area methods, and salt-concentration method.
Area-velocity methods measure cross-sectional area and velocity of flow to determine discharge.

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Description

Explore the key concepts of stream flow and runoff in hydrology. This quiz covers infiltration, overland flow, bank storage, and the characteristics of drainage basins. Test your understanding of how water moves through different components of a watershed.