Hydrological Soil Types

The term "hydrological soil types" has been introduced in the Jordan National Water Master Plan of 1978. These types are used to classify the different surface runoff behavior derived from the lithology of the top geological stratum.

The hydrological soil types have only been mapped for the western part of Jordan, for the eastern part they were deducted on the basis of the surface geology available for the entire country.

Class min
CN Description
1 0.1 0.3 69 sand, gravel
2 0.2 0.5 70 chert-limestone, sand-limestone
3 0.4 0.6 92 basalt, scoriferous
4 0.4 0.7 93 limestone, marl, chalk
5 0.5 0.8 90 sandstone, dolomite, limestone
6 0.8 0.9 91 sandstone, siltstone
7 0.7 0.9 94 marl, limestone
8 0.8 1.0 90 marl, silt, loam
9 1.0 1.0 96 granite

In the above table, minPhi and maxPhi indicate the range of runoff coefficients as estimated by the previous Water Master Plan.

CN is the Curve Number for surface runoff and AMC II as set by the current Water Master Plan after series of calibration runs. Curve number means a variable runoff coefficient that depends on the actual moisture saturation of the soil.

The spatial distribution of hydrological soil types is stored as Surfer Grid and forms the most important parameter for converting rainfall into surface runoff and deep infiltration. The CN-values as function of the hydrological soil types can be easily modified by the model interface.