Hydrology: Components of Stream Flow

The entire area of a river basin whose surface runoff drains into a river.

The boundary line separating two adjacent drainage basins, usually along a ridge.

The single point where all surface drainage from a basin flows into a stream.

The time it takes for rain at the furthest point of a drainage basin to reach the concentration point.

The number of streams per square kilometer in a drainage basin.

The total length of all stream channels (perennial and intermittent) per unit area of the basin.

How well a basin drains water, indicated by drainage density. Higher = better drainage.

A method for determining the slope of large drainage areas by dividing them into grids and counting contours.

Ratio of width to length in a given area.

Ratio of the perimeter of a region to its circumference; quantifies compactness.

Ratio of twice the radius to the length; measures how elongated or round the shape is.

Ratio of area to the area of an equivalent circle; quantifies shape similarity with a circle.

A stream that receives groundwater but does not release it.

A stream that releases groundwater.

A stream that flows continuously.

A stream that flows only at certain times of the year.

The portion of rainfall that flows over the land surface after losses from evaporation, interception, and infiltration.

Steep terrain, vegetation, storm direction, altitude, and land use affect how much water runs off.

The usable water after rain losses, for uses like irrigation or water supply.

The highest flow rate during a flood, happening when rainfall is intense and conditions favor runoff.

Different ways to predict how much water will run off, including empirical formulas, infiltration, rational method, and hydrographs.

Mathematical equations used to estimate runoff, often based on rainfall.

Estimating runoff by subtracting the amount of water that soaks into the ground from the total rainfall.

Water held in streams, channels, and low-lying areas, reducing the flood peak.

The shape of a drainage basin affects flood intensity and time of concentration. Fan-shaped basins have shorter concentration times and higher intensity, while fern-shaped basins have longer concentration times and more distributed discharge.

A dimensionless measure of a drainage basin's shape, independent of size, reflecting its form. It only depends on the basin's slope.

The average slope of a basin calculated using the number of contour intersections by vertical and horizontal lines, combined with the contour interval and total length of grid segments.

A dimensionless factor that specifies the shape of a basin, calculated by dividing the basin area by the square of its basin length or perimeter.

Drainage basin characteristics (like shape, size, and slope) influence the time lag of unit hydrographs and peak flow.

A hydrograph showing the direct runoff resulting from one unit (typically 1 cm) of excess rainfall over a specific duration, spread uniformly across a drainage basin.

The unit hydrograph method relies on several key assumptions about the basin and rainfall: uniform rainfall intensity, uniform distribution across the basin, constant base period for varying intensities, proportionality of runoff ordinates, and representation of basin characteristics.

The portion of rainfall that is not absorbed by the soil and contributes to surface runoff.

The time it takes for water from the furthest point in a drainage basin to reach the outlet point (usually the stream gauge).

An empirical formula used to estimate the time of concentration for a watershed, considering its length and slope.

The maximum rate of water flow in a stream during a specific event, typically measured in cubic meters per second or cubic feet per second.

A narrow section in a channel that accelerates the flow of water, allowing for precise measurement of low stream flows.

A structure built across a stream to create a controlled flow over a specific height, allowing for accurate measurement of stream flow.

A method for estimating flood discharge by analyzing the cross-sectional area of the river channel and the slope of the water surface.

An equation used in the slope-area method to calculate flow velocity. It relates Chezy's constant, hydraulic mean radius, and water surface slope.

An alternative equation to Chezy's equation used in the slope-area method to calculate flow velocity. It uses Manning's roughness coefficient, hydraulic mean radius, and slope.

Methods for estimating discharge through constricted sections like bridge openings or canal falls by measuring the water surface drop.

A factor that accounts for energy losses as water flows through constrictions.

The additional head (height) generated by the velocity of water as it approaches a constriction.

A technique for determining discharge by adding a chemical, like salt, to a stream and measuring its concentration downstream.

The process of ensuring the added chemical is evenly distributed throughout the water before measuring its concentration.