Free download, software on soil salinity irrigation, drainage

SaltMod	This is a mathematical, numerical simulation model describing the relations between agriculture, crop rotation, and irrigation. Factors like rainfall, potential and actual evaporation (evapotranspiration), climate, and hydrology play also a role. The model calculates depth and level of shallow water-table, capillary rise and deep percolation as well as the salt balance in the soil It gives graphs of soil salinity and subsurface drainage by drains or wells. There is ample attention regarding the reuse (conjunctive use) of ground and drain water from wells. Finally, the model includes farmers' responses to water logging and soil salinity.
SahysMod	This is a combination of Saltmod with a hydrologic model of ground water flow and hydraulics to account for large spatial variation through a network of polygons. It includes phreatic (unconfined) aquifers as well as soil layers with slow vertical hydraulic conductivity (soil permeability for water) resulting in semiconfined (leaky) aquifers.
SaltCalc	This is simplified version of SaltMod with the advantage that calculations are made for shorter time steps (monthly instead of seasonally or even daily). SaltCalc can be used when field observations of irrigation, sahallow water table and soil salinity have been made and one wishes to develop a model for that situation and for the maintenance of the salt balance in the soil. Normally, calibration of unknown values must be done using a range of values of the corresponding variable, running the model repeatedly and selecting the optimal value from the range that gives model results closest to observed values.
PolySalt	This is simplified version of SahysMod with the advantage that calculations are made for shorter time steps (monthly instead of seasonally). The application principles are similar as those described before under "SaltCalc".
LeachMod	This model is somewhat similar to SaltCalc. On the one hand the water management options are fewer (e.g. re-use of drainage or well water for irrigation do not feature here), but the model is more modern in the sense that the variable input for each time step is given in a table so that the calculations over all the time steps are done in one go. Moreover, by inserting the observed values of soil salinity in the data table, the model optimizes the leaching efficiency of the soil automatically so that the optimal salt balance can be found.

RainOff	This helps in hydrologic modelling of effective rainfall, recharge, and water storage. It calculates runoff, surface drainage and discharge relations in hydrological catchment areas (watersheds) using the concept of a nonlinear reservoir. It contains a calculator for agricultural drainage systems with pipes and ditches.
NashMod	The NashModel, like RainOff, calculates surface runoff and stream flow from rainfall. However, instead of a non-linear reservoir it uses a cascade of linear reservoirs, an idea elaborated by Nash. In some cases it yields better results than RainOff, but in other cases absolutely not. The model was developed recently and put on this website on 17 August 2017.
FloodRoute	This hydraulic model does calculations on flood wave transport in a river or channel section. The model is based on the concept of a non-linear reservoir having an outflow function with two parameters. Given the inflow and outflow waves the parameters will be given an optimal value securing the best fit of the observed and similated (calculated) outflow wave. Once the parameters are well established, they can be used to predict the outflow wave for any conceived inflow wave.
EnDrain	This hydrologic model does calculations on steady-state discharge by horizontal subsurface drainage systems, hydraulic head, as well as depth and level of water-table in agricultural land. It comes up with a drain spacing using the energy balance of groundwater flow, but also the Darcy and continuity equation (mass balance/budget of water). It includes drain entrance resistance and soil anisotropy of hydraulic conductivity (soil permeability for water), i.e. the horizontal and vertical hydraulic conductivity are different. All is applicable to pipe/tile drains (drain pipes) and open ditches for the control of the shallow water table.
DrainCalc	This hydrologic model does calculations on non-steady (transient, fluctuating) state discharge by horizontal subsurface drainage systems in agricultural land. The changes in hydraulic head (level of the water table) are also simulated. The model uses the concept of a non-inear reservoir, like in the RainOff program. This reservoir is characterized by reaction factor of discharge and hydraulic head (watertable height) on the recharge varying in time. The program calculates the reaction factor from discharge and head data, or it calculates discharge and head given the parameters of the response function. In addition, it provides the facility to find the response function from the parameters of the drainage system. All this is applicable to pipe/tile drains (drain pipes) and open ditches for the control of the shallow water table.
HydrCond	This is a calculator for the hydraulic conductivity of soils based on measurements of discharge and level of the ground water table in agricultural subsurface drainage systems.
WellDrain	This hydrologic model calculates the spacing of wells, the shape, depth, and level of the watertable in vertical drainage systems using pumped wells. Like EnDrain, it permits aquifers with various different properties and, in addition, fully/partially penetrating wells.

CumFreq	This calculator is meant for segmented (in splines, piecewise)cumulative frequency analysis using a breakpoint which serves for example to study discontinuous probability distributions and return periods. It can anlyse hydrologic factors like rainfall, river and drain discharge, water and river level. Also the depth or level of watertable, soil salinity, and the hydraulic conductivity (i.e. soil permeability for water) can be sudied. The calculator uses 20 different probability distributions and selects the best fitting. Preference for a certain distribution can also be expressed. An amplified version (CumFreqA), permitting to express preference for advanced composite distributions, can be made available on request.
NormDis	This is a two-way calculator for normal probability distributions with graphics: Value => Probability, and Probability => Value. The calculator can be used for many kinds of statistical probability analysis.
SegReg	This calculator can be used for segmented linear regression, i.e. regression in segments (splines), using a breakpoint (break-point) or threshold value, which serves for example to analyse the relation between plant growth or crop production in agriculture versus soil salinity and depth of watertable in agricultural land. The calculator analyses 2x6 different types of models and selects the best fitting. An amplified version (SegRegA), permitting to express preference for a certain model, and allowing S-curve (sigmoid), power, quadratic and cubic functions can be made available on request.
PartReg	This software is similar to SegReg but it emphasizes the horizontal part in Type 3 and Type 4 relations with the aim to define crop tolerance levels more precisely and to find the maximum range of "no effect". Further explanation is given on the PartReg page.
F-test calculator	This is a calculator for the Fisher's F-test as used in analysis of variance (Anova). The above SegReg model uses this test for the significance of the regression. Like NormDis, it is also a two-way calculator: F-value => Probability, and Probability => F-value.
t-distribution calculator	This is a two-way t-distribution calculator to perform a t-test on the significance of the difference between means (averages) of series of data using Student's t - probability distribution : t-test-value => Probability, and Probability => t-test-value.
R-squared calculator	This is a calculator for the confidence interval of the R squared value being an indicator for the goodness of fit of a function derived from a data set. R squared is also called coefficient of determination (explanation) and it is based on R, the correlation coefficient.