The presence of CaCl2 should have no (or minimal) influence on pH and alkalinity as it ionizes to strong (fixed) ions with no change in electrical charge balance. I"m aware of no way to measure CaCl2 directly. There are various ways to measure Ca ion concentration (calcium electrode, atomic absorption spectrometer, flame photometry). Chloride ion concentration is more difficult, esp. at very low levels - the usual method (Mohr Method) involves titration with silver nitrate, but electrometric titration is commonly used in clinical and analytical labs ( http://www.gsisinc.com/posecom/products.php?product=Buchler%252dCotlove-Chloridometer%2C-Parts;http://www.sciencedirect.com/science/article/pii/S0003267000869597 ). If you are analyzing natural water containing various cations and anions, you will likely have to measure as many of those as possible to determine how much of the Cl is associated with (i.e., dissociated from) Ca.

Thank you Dr. Charles.

We are diluting CaCl2 with water(CaCl2 +H2O = CaO + 2HCl) and spray in fruit trees to prevent the fruit cracking. After each rain we need to spray CaCl2. Thus, we want to calculate the amount of CaCl2 washed out by rain. If we know washed out concentration we can spray reduced CaCl2 concentration after first rain.

    For us Ca is the main concern because it reduces the fruit cracking. 

If that is your only salt, then conductivity will give you a measure of CaCl2 concentration. You can just prepare some conductivity standards with different concentrations of CaCl2 and construct a standard curve.  Alternatively, the CRC Handbook of Chemistry and Physics should have a table of chemical and physical properties of CaCl2 solutions, including conductivity values, over a wide range of concentrations.