What is overland flow in hydrology?
Definition. Overland flow is the movement of water over the land, downslope toward a surface water body. Overland flow is a very important aspect of the water cycle and can be generated under two different physical mechanisms.
What is the difference between overland flow and stream flow?
OVERLAND FLOW AND STREAMFLOW. Runoff that flows down the land slopes in broadly distributed sheets is called overland flow. This is different from streamflow, in which the water runs along a narrow channel between banks.
Is overland flow the same as sheet flow?
Sheet flow . (also called overland flow) means shallow, unconcentrated and irregular flow down a slope. The length of strip for overland flow usually does not exceed 200 feet under natural conditions. Sheet flow means runoff which flows over the ground surface as a thin, even layer, not concentrated in a channel.
What is the difference between overland flow and interflow?
Interflow occurs when water infiltrates (see infiltration (hydrology)) into the subsurface, hydraulic conductivity decreases with depth, and lateral flow proceeds downslope. As water accumulates in the subsurface, saturation may occur, and interflow may exfiltrate as return flows, becoming overland flow.
How do you calculate overland flow?
The average length of overland flow was determined by dividing the watershed area by twice the total length of all waterways.
What are the two types of overland flow?
Overland flow is the term used to describe surface flow that is outside the confines of a stream channel. The generation of overland flow is traditionally divided into two primary mechanisms, infiltration excess (Horton; after Horton (1945)) and saturation excess (Dunne; after Dunne and Black (1970a, 1970b)).
What is overland flow distance?
From the sketches of Figure 7-10 it should be clear that the overland flow length is the distance from the boundary of the idealized rectangle to the drainage conduit (pipe or channel). It is along the overland flow length that the surface gradient should be estimated.
How do you calculate flow length?
This distance is measured along the direction of flow, not “as the crow flies”. Definition (GIS): In GIS, the flow length of an arbitrary pixel is determined by summing the incremental distances from center-to-center of each pixel along the flow path from the selected pixel to the outlet pixel.
What is the difference between Hortonian and saturation overland flow?
Hortonian overland flow (HOF) commonly occurs in arid regions. Saturation overland flow (SOF) commonly occurs in humid regions. Reports that SOF takes place in semiarid regions are critically analyzed. The possible occurrence of SOF in semiarid regions should be re-examined.
How do you calculate overland flow distance?
Quote: The average length of overland flow was determined by dividing the watershed area by twice the total length of all waterways.
How is overland flow measured?
Measuring overland flow Overland flow can be assessed using a length of plastic guttering. Choose a 50cm or 1m long length, with both ends closed. Bury the guttering just in the soil so that the upper edge is parallel with the soil surface. Cover the open top of the gutter with a plastic cover to keep out the rain.
What are the 2 types of overland flow?
What increases overland flow?
Animated Examples of Saturation Excess Overland Flow: Increased interflow levels due to precipitation inputs. Elevated water table due to increased water inputs. Exceeded water holding capacity in shallow soil.
How does overland flow happen?
when the intensity of precipitation that reaches the surface exceeds the infiltration capacity of the soil. This process is known as Hortonian overland flow. 2. when the combination of precipitation intensity and duration (and run-on from higher areas) saturates the soil and raises the water table to the surface.
How do you determine if a flow is laminar or turbulent?
For practical purposes, if the Reynolds number is less than 2000, the flow is laminar. If it is greater than 3500, the flow is turbulent. Flows with Reynolds numbers between 2000 and 3500 are sometimes referred to as transitional flows. Most fluid systems in nuclear facilities operate with turbulent flow.
How can overland flow be controlled?
A suite of best management practices for reducing overland flow may include actions to increase surface roughness and canopy interception, maintain soil porosity, and otherwise disperse concentrated or fast-moving flows of water.