4.4 Simulation of the Functioning of the Network
Analysis of the network shows that the total length of the
networks is 7 056 m and that the total amount of water that could be
transported in the whole network is 5 313 m3/h. With a simulated
manometric height of 240 m, the service pressure is 24 bars, while the total
head losses in the network is 19.7 m. This gives a loss in pressure of
approximately 2 bars. The flow velocity in the various branches vary from 0.8
m/s - 1.1 m/s and are in accordance with the norm ( ) for flow in closed
conduits described by Zoungrana, (2002).
The different parameters calculated and the hydraulic
characteristics of the network are presented in Appendix III. The flow
velocities, the roughness coefficient, the deviation in pressure at the level
of the hydrants, the cumulated head losses and the total manometric height are
the principal characteristics emphasized on.
The manometric height of the pumping station is obtained as
the difference between the retained piezometric elevations upstream and the
geometric elevation of the pumping station. Where ever the manometric height
considered is less than that which is calculated, the network is said to be mal
functional. Where total head losses in the pipe are less than 10% of the
service pressure at the pumping station (HMT), and where there exist
insufficient pressures in a hydrant, a suppressor will be needed in order to
increase the available pressure at the hydrant. Where head losses are greater
than 10% of service pressure at the pumping station and that the pressures at
the hydrants are sufficient or not, these pressures need to be reduced.
4.5 Spatial Representation of some Queries on the
Irrigation System
The database created helps the irrigation manager to inquire
information related to irrigation project in GIS environment. Either Permanent
data or yearly changing data can be inquired in the database. Some examples of
created queries are as follows:
- Parcel irrigated during a given production year
- Crop pattern under selected channel
- Geographical position of plot valves
- Type of irrigation systems in various plots
- Crop pattern under selected parcel
4.5.1 Spatial representation of crop coefficients
The sensibility of crops to water stress is represented
spatially as show in Figure 4.4 by considering the crop coefficients for the
various production plots and the soil types involved. This helps managers in
the localization of plots with critical conditions and hence enhances decision
making. Thus, in the case of water shortage and only few plots could be
irrigated, the plots with a critical response to stress will be satisfied
first. This done through a query of the database and the result presented in
the GIS. Figure 4.4 therefore illustrates that in order to take a management
decision for irrigation, the plots shaded in green on the map have to be
irrigated before those in orange. These plots either have plants with a higher
vulnerability to water stress or are found on plots whose soils are of light
texture and thus need frequent irrigations.
| 
