Rainfall manager
The rainfall manager is where the user can store rainfall data (gauged rainfall, IDF curves, gridded rainfall) and create synthetic rainfall.
The rainfall manager data are saved on the disk under a specific file that is still the same with any projects. Files of external data imported in the rainfall manager have their path saved as relative path. This allows keeping rainfall from one project to others. When opening Lekan (new project or with an existing project), the rainfall manager load always the same file and this file is the last saved one. It is also possible to open another file, and then this one will be loaded by default for the next start of Lekan. But it is recommended to work with the same file to avoid bad reference to a rainfall if the user changes the file during editing a project.
The rainfall manager is a tree of different types of element:
- Zone: this type represents a geographical zone (what the user wants: country, region...). A zone can contain other zones, stations or gridded rainfall.
- Station: this type, that can be locaized by a point in the map, contains the rainfall data: gauged rainfalls, IDF curves and/or synthetic rainfalls
- IDF curves: element that contains Intensity Duration curves
- Intensity Duration Curve: parametric equation used to obtain the intensity of rainfall depending on its duration
- Gauged rainfall: rainfall data with constant time step that can be filled manually by user or imported from files
- Synthetic rainfall: rainfall that is designed depending on Intensity Duration curve(s) and/or other parameters
- Gridded rainfall: rainfall defined spatially by values on a grid of fixed resolution and for different time step. These data are usualy coming from radar or forecast model.
Zones, stations and IDF curves elements are container of data. These elements are only defined by a name and a description (optional).
All the items can be added/removed through a the context menu after a right click on the tree.
Stations contain all the rainfall data: IDF curves, gauged rainfalls, or synthetic rainfalls. A station can be geolocalized with a point on the map canvas. Once the rainfall manager is opened, each geolocalized rainfall station is associated with a marker on the map canvas.
To add a station, the user has the following possibilities after a right-click on a zone item:
- Add Station: a non-geolocalized void station will be added.
- Add Station from: a geolocalized station will be added after the user picks a point on the map canvas.
- From Deflt-FEWS: after choosing a XML Delft-FEWS file, the user can load existing gauged data from the file in a new associated geolocalized station (see Delft-FEWS provider)
Intensity Duration curve doesn't have name but have a return period. This return period is used for displaying the curve in the rainfall tree.
To define the intensity of rainfall depending on the duration, Lekan support, for now, two parametric equations :
Montana : 
Sherman : 
For each of this formula, the variable 't' is the rainfall duration and the user can create several duration intervals for which the parameters (a, b, c, n ...) have to be entered. To add an interval, double-click on the green cross 
.
As for this formula, depending on who has evaluated the parameters, the unit time of the duration can be different from the intensity's unit time. The user can set the unit time for the entry and the unit time for the result corresponding to the parameters. Defaults are minute for entry duration and hour for intensity result (that is mm/hours).
Gauged rainfall is rainfall with a constant time step with values from a rain gauge station or defined by the user as wanted.
The reference time, that is date/time when the rainfall starts, has to be entered. The user must also define the time step.
Then the user can enter value one by one or copy/paste in the table.
The value can be the incremental height per time step or the intensity for each time step. If the intensity is chosen, the time unit has to be also set.
Since Lekan 2.2, the user can import rainfall data from XML files created by Delft-FEWS software, see Delft-FEWS provider.
It is also possible to import rainfall from a text file by pushing the corresponding button 
.
Once this window open, the first step is to choose a text file.
If there are several columns in the files, it is necessary to choose one or many delimiters: choose or fill a delimiter and press 
to add it to the list of delimiters. To remove a delimiter, select or fill it and press 
.
Then, set the line number of the header line (if none, set 0) and the line number corresponding to the data's beginning.
The preview table allows the user to control the settings and to choose the field. Once the field is selected, pressing under the field choice send the data in the rainfall tab. Here the user has to set :
- name and description of the rainfall (description is optional)
- the time step of the data
- the reference time of the data, that is the date/time when the gauged rainfall start
- the type value: height per time step (incremental) or the rainfall intensity, both have to be in millimeter
In the end, the user has to choose a station where to import the rainfall (it is necessary to create this station before opening the import window).
Lekan allows the possibility to designed specific rainfall with the following methods :
- Chicago method
- Alternating block method
- Double triangle method (Desbordes)
To designed these rainfalls, the user has to set:
- an Intensity Duration curve, the user can choose from the existing one by pushing the button
- a time step
- a total duration
- an eccentricity coefficient, between 0 and 1, 0.5 is for a central peak.
This rainfall is based on two duration: a total duration that is all the rain duration, and an intense duration that is a peak with a shorter duration. Those two duration are associated to a return periods that can be different, generally, the intense one is greater than the total one. The shape of this designed rainfall is a double triangle.
To designed this rainfall, the user has to set:
- a time step
- an intense duration
- a total duration
- an Intensity Duration curve for the intense duration and another for the total duration, the user can choose them from the existing one by pushing the buttons
- an eccentricity coefficient, between 0 and 1, 0.5 is for a central peak.
Also called gridded precipitation, this data is based on a grid with a fixed resolution where values vary spatially and temporaly following time step. These data are usually coming from radar or forecast models. These type of data can be imported to Lekan and then used by applying these rainfall on watershed or 2D flow model that support gridded precipitation.
The supported format of gridded rainfall that can be read by Lekan are the following:
- COMEPHORE (TIFF files): radar hourly gridded rainfall from Météo-France.
- GRIB2 format: the user has to specify the variable corresponding to the rainfall and the type of provided data (cummulative heigth, incremental heigth or intensity).
- DSS format: the format used by HEC softwares to store data, notably gridded precipitation.
To import a rainfall the user can right click on the zone and choose "Import gridded rainfall" on the context menu. Then, after choosing a compatible file, specific format options can be set and the gridded rainfall is visible on a map. The user can also set the color of its choice.
All imported rainfall can be exported, allowing the user to convert any format to the writable format. For now, only DSS format is writable by Lekan. To export a rainfall, the user right clicks on the gridded rainfall and choose "Export gridded rainfall". Then different option can be set to export the rainfall:
- Coordinate reference system
- Extent of the rainfall
- Resolution
- Start and end time to export