You can use a simple water balance equation to assess deep percolation with some general assumptions on soil heterogeneity. Some additional information that you might need to collect is evapotranspiration (ET) levels. Do you have any surface impoundments? How is the groundwater flow in the location? If I assume these are not significant, Deep percolation should roughly equal (Rainfall-Runoff-ET)+ Change in soil storage + Change in surface storage. You might need to fit the equation for each event and maybe test it with some experimentation using lysimeter to reassess any missing variables.

Conventionally, it is assumed that deep percolation (or more appropriately drainage below the depth of interest) is assumed to take place only when soil moisture is greater than the 'field capacity' of the soil profile. Field capacity - defined as the moisture content at which gravity drainage ceases, may be determined from the soil water retention curve as the moisture content at 10 -33 kPa soil water tension. Alternatively, it may be estimated from standard values for a given soil class as per the USDA triangle. 

Then as suggested by Prof. Randhir, a simple water balance may be calculated by accounting for rainfall, irrigation, runoff, evapotranspiration and profile soil moisture may be calculated. If this calculated soil moisture is greater than field capacity, the difference between them may be assumed to represent drainage. 

First you have to estimate the infiltration rate upon soil type. Then apply water blance equation.

thank u for all Mr.s ... 

If i used follow eq, that the result become more realistic or do not have relation to it:

deep percolation = Infiltration - Soil moisture content directly after rainfall event.

if that they used only soil depth (10 cm).

 thank u.

In my opinion, firstly you have to refer the  deep percolation process to the multiscale conceptual model, at basin, catchment, hillslope or parcel scale. Then, you can apply the proper balance equation considering all the runoff components significant at  these different space-scales and at event time-scale, considering complexity, connectivity, threshold-conditioned behaviour in hydro-geomorphological response of the unit considered. 

Article Using geomorphometry for hydro-geomorphological analysis in ...

thank u Mr. Domenico Guida

First of all, what is you region – somewhere in Iraq? The important issues are: climate (Iraq is characterized mostly with desert and semi-arid climate), rainfall distribution, land use (irrigated crops or not) - http://siteresources.worldbank.org/INTWAT/Resources/Iraq.pdf

Deep percolation is groundwater recharge – see papers of Doll and Fiedler (for Iraq they give in average 17,9 mm annually): https://hal.archives-ouvertes.fr/file/index/docid/305174/filename/hess-12-863-2008.pdf

You may look at the simulated average groundwater recharge by PCR-GLOBWB globally: http://onlinelibrary.wiley.com/doi/10.1029/2010GL044571/full

Is your region is located in northern Iraq, with karstified rocks? In this case the next paper will be useful: Stevanovic, Z., & Iurkiewicz, A. (2009). Groundwater management in northern Iraq. Hydrogeology journal, 17(2), 367-378.

I suppose that you intend to work on daily time step. You may use HYDRUS model, but it requires many parameters.

Sarbast Ismael Abdi

Deep percolation can be determined from the parameters of the soil water balance be it under rain-fed or irrigated condition. Using the soil water balance equation below:

ΔS = P- ET - DP

Rearranging it when all variables are known, deep percolation will be computed by

DP = P + I - ET - ΔS

Where P-Precipitation will be obtained from the sites meteorological weather station, DP-deep percolation, ΔS-change in storage calculated as difference initial and final moisture content over fortnightly and ET-evapotranspiration can be calculated using any method of determining reference evapotranspiration.

Below the rooting zone the soil water pressures vary little with time and hence a condition called the fixed gradient exists. Thus, knowing the K(Θ) function and the water content, Θ the percolation rate can be computed. One can also estimate the K(Θ) function using Θ measured at 15 minute intervals. Need more information?