SAHYSMOD SPATIAL AGRO-HYDRO-SALINITY MODEL
 
Description of Principles, User Manual,
and Examples of Application

 
Sahysmod is a computer program for the simulation and prediction of the salinity   
of soil moisture, groundwater and drainage water, the depth of the water-table
and the drain discharge in irrigated agricultural lands under different geo-
hydrologic conditions, varying water management options, including the re-use
of groundwater for irrigation by pumping from wells (conjunctive use),and
several cropping/irrigation rotation schedules, whereby the spatial variations
are accounted for through a network of polygons.
    The mathematical model also calculates actual from potential evaporation
(evapotranspiration), capillary rise, deep percolation, and groundwater flow.
     Optionally, farmers' responses to irrigation and agriculture can be simulated.
Sahysmod combines the agro-hydro-salinity model SaltMod and the polygonal
ground water model SGMP of my colleague Dr.J.Boonstra.
It allows for the introduction of semi confined aquifers.
 
On web site www.waterlog.info For free downloads see the SahysMod page                  
 
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TABLE OF CONTENTS
 
1. INTRODUCTION
 
2. PRINCIPLES
2.1. Model components
2.2. Polygonal network
2.3. Seasonal approach
2.4. Computational time steps
2.5. Hydrological data
2.6. Cropping patterns/rotations
2.7. Soil strata
2.8. Agricultural water balances
2.9. Ground water flow
2.10 Drains, wells, and re-use
2.11 Salt balances
2.12 Farmers' responses
2.13 Annual input changes
2.14 Output data
2.15 Other users' suggestions
 
3. AGICULTURAL WATER BALANCES
3.1. The reservoir concept
      3.1.1. The surface reservoir
      3.1.2. The root zone
      3.1.3. The transition zone
      3.1.4. The aquifer
      3.1.5. Topsoil water balance
      3.1.6. Subsoil water balance
      3.1.7. Agronomic water balance
      3.1.8. Geo-hydrologic water balance
      3.1.9. Overall water balance
3.2. Model calculations for water balances
3.3. Capillary rise and actual evapo- transpiration
      3.3.1. Depth of the water table and capillary rise factor
      3.3.2. Potential evapo-transpiration and moisture deficit
      3.3.3. Apparent capillary rise and actual evapo- transpiration
      3.3.4. Capillary rise
3.4. The subsurface drainage
3.5. Water balance of the transition zone
3.6. Irrigation efficiencies and sufficiencies
 
4. GROUND WATER FLOW
4.1. Finite difference method
4.2. Incoming and outgoing groundwater flow
      4.2.1 Between two unconfined aquifers
      4.2.2 Between two semi-confined aquifers
      4.2.3 Between unconfined and semi confined aquifers
      4.2.4 Inflow and outflow per polygon
      4.2.5 Vertical flow in semi-confined aquifers
4.3. Inflow of salt
4.4. Change of ground water level
4.5. Seasonal values
4.6. Possibilities of and conditions for application
 
5. SALT BALANCES
5.1. Change in salt content
5.2. Salt balances under full cropping rotation
      5.2.1. Above the soil surface
      5.2.2. Root zone
      5.2.3. Transition zone
      5.2.4. Aquifer
      5.2.5. Salt concentration of drain and well water
5.3. Salt balances under zero cropping rotation
      5.3.1. Above the soil surface
      5.3.2. Root zone
      5.3.3. Transition zone
5.4. Salt balances under intermediate cropping rotations
      5.4.1. Types of cropping rotation
      5.4.2. Part of the area permanently non-irrigated, Kr=1
      5.4.3. Part of the irrigated area permanently under A crop(s)
      5.4.4. Part of the irrigated area permanently under B crop(s)
 
6. SPATIAL FREQUENCY DISTRIBUTION OF SOIL SALINITY
 
7. FARMERS' RESPONSES
7.1. Reduction of irrigated area when salinization occurs
7.2. Reduction of irrigation when water logging occurs
7.3. Reduction of ground-water abstraction by pumping from wells     
 
8. ALPHABETICAL LIST OF SYMBOLS
 
9. USER MENU
9.1. The main menu
      9.1.1. The input menu
9.1.2. Network map
      9.1.3. Calculations
      9.1.4. The output menu
9.2. Editing the input
      9.2.1. Title of data
      9.2.2. Main model properties
      9.2.3. Duration of the seasons
      9.2.4. Overall system geometry
      9.2.5. Nodal network relations
      9.2.6. Internal system properties
      9.2.7. Hydraulic conductivity
      9.2.8. Total porosity in soil strata
      9.2.9. Effective porosity in soil strata
      9.2.10 Leaching efficiency in soil strata
      9.2.11 Storage efficiency in crop land
      9.2.12 Indices of agricultural practices
      9.2.13 Properties of subsurface drainage system
      9.2.14 Initial salinity root zone
      9.2.15 Initial salinity sub-soil
      9.2.16 Init. hydr. head & crit. depth water table
      9.2.17 Aquifer inflow/outflow conditions
      9.2.18 External boundary conditions
      9.2.19 Rainfall and potential crop evaporation
      9.2.20 Surface inflow/outflow/drainage
      9.2.21 Well discharge, subsurface drainage control
      9.2.22 Irrigated area fractions and rice cropping
      9.2.23 Irrigation and field application
      9.2.24 Re-use of drain and well water
      9.2.25 Map of the nodal network
9.3. Inspecting the output
      9.3.1. Nodal characteristics
      9.3.2. Soil salinity root zone
      9.3.3. Salinity transition zone and aquifer
      9.3.4. Other salinity
      9.3.5. Ground water levels, depth of water table
      9.3.6. Groundwater flows, net recharge
      9.3.7. Drain and well discharge
      9.3.8. Field percolation to the sub-soil
      9.3.9. Capillary rise into the root zone
      9.3.10 Canal and field irrigation
      9.3.11 Irrigation efficiencies and sufficiencies
      9.3.12 Crop area fractions, rotation key
      9.3.13 Scroll through the entire output file                                                                   
 
10. LIST OF SYMBOLS OF INPUT DATA
 
11. LIST OF SYMBOLS OF OUTPUT DATA
 
12. EXERCISE ICMALD
12.1. Introduction
12.2. Input
12.3. 1st Inspection of the output
12.4. Canal lining
12.5. Interceptor drain
12.6. Salt movement in the ground water
12.7. Checking the drainage flow by hand
12.8. Checking the capillary rise by hand
12.9. Checking the groundwater flow by hand
 
13. CASE STUDY HANSI FARM
13.1. Introduction
13.2. Aquifer recharge
13.3. Drainage discharge
13.4. Epilogue