Difference between revisions of "Module Runoff"
From MohidWiki
(→Main Processes) |
(→Main Processes) |
||
| Line 5: | Line 5: | ||
The overland surface runoff is calculated at the interface of the grid cells and it is obtained by applying the Manning's equation as follow: | The overland surface runoff is calculated at the interface of the grid cells and it is obtained by applying the Manning's equation as follow: | ||
| − | |||
:<math>\[Q=\frac{1}{n}\cdot A\cdot R_{h}^{2/3}\cdot s^{1/2}</math> | :<math>\[Q=\frac{1}{n}\cdot A\cdot R_{h}^{2/3}\cdot s^{1/2}</math> | ||
Revision as of 23:44, 1 March 2011
Contents
Overview
Module Runoff allows the calculation of the overland surface runoff over a regular structured grid as function of the water column and terrain slope. The water column, namely the water located above the terrain, is given by the Module Basin where the precipitation is converting into a water column considering the losses due to the evapotranspiration and the infiltration processes. In particular the overland flow is evaluated by the Manning’s equation.
Main Processes
The overland surface runoff is calculated at the interface of the grid cells and it is obtained by applying the Manning's equation as follow:
- Failed to parse (unknown error): \[Q=\frac{1}{n}\cdot A\cdot R_{h}^{2/3}\cdot s^{1/2}
where:
Q is the overland flow (m3/s) A is the area of the cross-section (m2) n is the Manning coefficient (s/m1/3) Rh is the hydraulic radius (m) S is the slope of the water surface (m/m)
In order to apply the Manning's equation each grid cell is considered as an open channel as shown in the scheme below.
where:
H is the water column (m) W is the cell width (m)
The hydraulic radius is the following:
- Failed to parse (unknown error): \[R_{h}=\frac{w\cdot h}{w+2\cdot h}
In according with the figure 1. the width is 'much' grater than the water column (w>>h) and the hydraulic radius can be considered only Rh=h. Therefore the Manning's equation can be simplified as:
- Failed to parse (unknown error): \[Q=\frac{1}{n}\cdot w\cdot h^{5/3}\cdot s^{1/2}
Regarding the slope to introduce in the formula is evaluate
In order to apply this formula each cells is consider like a open channel where the water level is given by the water column and the slope in the two directions X,Y is given by the difference of the slopes' interfaces. The roughtness of the terrain is given by the manning coefficient ans it is obtained by the land use map by a gis process.
The runoff is calculated by the Manning's equation as follow:
In order to apply the manning formula
Other Features
How To Generate Manning Coefficients
Manning coefficients must be provided in runoff data file.
Options:
- Use a constant value
- Define a Manning's grid: One possible option is to associate Manning with land use classes (shape file). In this case can use MOHID GIS going to menu [Tools]->[Shape to Grid Data] and provide: i) the grid (model grid), ii) the land use shape file and iii) the corespondence between land use codes and Manning.
Use Manning inicialization with Module FillMatrix standards in the block:
<BeginOverLandCoefficient> FILE_IN_TIME : NONE INITIALIZATION_METHOD : ASCII_FILE REMAIN_CONSTANT : 1 DEFAULTVALUE : 0.08 FILENAME : ..\..\GeneralData\Runoff\Mannings200m_v2.dat <EndOverLandCoefficient>
