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# SAHYSMOD PowerPoint PPT Presentation

SAHYSMOD. Spatial Agro-Hydro-Salinity Model. INTRO. Sahysmod working group. Polygons. The principle of Sahysmod is a network of noda l points (nodes) with coordinates. Then, polygons are made around the nodes using the principle of Thiessen. In each polygon:

SAHYSMOD

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## SAHYSMOD

Spatial Agro-Hydro-Salinity Model

### Polygons

The principle of Sahysmod is a network of nodal

points (nodes) with coordinates.

Then, polygons are made around the nodes

using theprinciple ofThiessen.

In each polygon:

• Saltmod is applied separately

• Groundwater flow is calculated from water levels in neighbouring polygons and hydraulic conductivity between the polygons using small time steps.

### Case study Icmald

• In case study Icmald there is only one line of internal polgons surrounded by external polygons for boundary conditions.

• The hydraulic conductivity between internal and external polygons is made zero so that the flow can not spread out, it is only in one direction.

• This pattern is useful to calculate conditions in a cross-section over a valley from upland to the bottom land and river

### Details Icmald

• In the centre of the area, from left to right, there is a leaking irrigation canal.

• In the downstream part of the area there are waterlogging and salinity problems

• First we simulate the effect of canal lining.

• Secondly we simulate the effect of interceptor drain along the canal.

• The results are shown in the next table

### Results

• We can see that canal lining and interception drainage have a small effect in the lower part, because the infiltration losses from the canal are small compared to the deep percolation losses from field irrigation in the upper area.

• In the lower part there is little irrigation due to waterlogging and salinity. If we increase the irrigation for reclamation and cropping, the watertable will become very shallow again.

• Canal lining or interception drainage are not sufficient to cure the problem.

• If enough irrigation water is available, the lower part can be reclaimed using normal drainage system or wells. This can also be simulated.

### Hansi case study

• In Hansi Farm, there is natural drainage through the aquifer to the neighbouring areas because the water level in Hansi is higher.

• The neighbouring areas recieve upward seepage of groundwater and are in danger of salinization.

• Sahysmod was used to determine drain discharge at different drain depths of possible drainage systems in Hansi Farm.

### Results from Hansi case study

• It was found that deeper drains discharge more water because the waterlevel is lower and underground outflow is less.

• When the drainage level is deeper than 2 m, in some polygons the natural underground outflow changes into underground inflow, causing upward seepage of ground water, so that the drain discharge is even more.

• Some data are given in the next slide

### Some data from Hansi results

• In polygon 1 the water table drops from 3.0 m depth to 3.2 m depth even though the drain discharge is always zero. This shows that polygon 1 does not need drainage, but some water from polygon 1 goes to the drains of neighbouring polygons. by drainage other polygons.

• In polygon 8, the present groundwater outflow is 2.8 m/year. This indicates excessive irrigation.

• In polygon 12 the drain discharge without drainage system is only 0.46 m/year. With drainage level at 2 m. depth it is 4.3 m/year. Hence, deep drainage attracts much water from neighbouring nodes.

• Hence, the drain discharge is influenced by the drain depth.

### SUMMARY

• Sahysmod can be used for many different situations and purposes.

• Only two examples were given and only a few aspects of these examples were discussed.

• Also the program itself can be downloaded freely from this website under Software

### Notes

• The outcomes can be checked by hand, even though the calculations are tedious.

• The output of Sahysmod can be saved in spreadsheet files. These can be used for further analysis in: