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the design drain spacing (L) can be found from the equation in dependence of the drain depth (Dd) and drain radius (r). Drainage criteria One would not want the water table to be too shallow to avoid crop yield depression nor too deep to avoid drought conditions. This is a subject of drainage research.
Drainage gradient (DG) is a term in road design, defined as the combined slope due to road surface cross slope (CS) and longitudinal slope (hilliness). Although the term may not be used, the concept is also used in roof design and landscape architecture. If the drainage gradient is too low, rain and melt water drainage will be insufficient.
Proper spillways help with flood control, prevent erosion at the ends of terraces, outlets, and waterways, reduce runoff over drainage ditch banks and are simple to construct. However, they can only be constructed at sites with natural drainage and moderate temperature variation and have a shorter life expectancy than other spillways.
The slope of the water table is known as the “hydraulic gradient”, which depends on the rate at which water is added to and removed from the aquifer and the permeability of the material. The water table does not always mimic the topography due to variations in the underlying geological structure (e.g., folded, faulted, fractured bedrock).
It uses a combination of the energy, momentum, and continuity equations to determine water depth with a given a friction slope (), channel slope (), channel geometry, and also a given flow rate. In practice, this technique is widely used through the computer program HEC-RAS , developed by the US Army Corps of Engineers Hydrologic Engineering ...
Manning's equation is an algebraic equation that predicts stream velocity as a function of channel roughness, the hydraulic radius, and the channel slope: = / / Darcy's law describes steady, one-dimensional groundwater flow using the hydraulic conductivity and the hydraulic gradient:
Drainage density is a quantity used to describe physical parameters of a drainage basin. First described by Robert E. Horton , drainage density is defined as the total length of channel in a drainage basin divided by the total area, represented by the following equation:
"Over a mile long reach [of the water channel] adds up to over 1.5 acre of land needed for the two stage drainage ditch design". This acreage of land may already be currently used for other purposes or contains infrastructure and subsurface gas or sewer lines. Thus, the larger the channel is, the more soil, and thus, increased funds required to ...