1 Professor of Faculty of Natural Resources, University of Tehran, I.R. Iran

2 Postgraduate Student of Watershed Management, University of Tehran, I.R. Iran

3 Postgraduate Student of Watershed Management, University of Shahr-e-Kord, I.R. Iran

4 Msc. of Desert Management, I.R. Iran


Physical characteristics of drainage basins such
as geological materials, landuse type and vegetation cover, soil type, surface
permeability, depth of underground water table, topographical conditions and
drainage are important factors in flood occurrence which affect prevailing
equations on water movement in drainage and determine storage capacity of
drainage basins. Geology is one of the most important factors affecting flood
occurrence of drainage basin. In this study it is attempted to investigate the
effect of geology factor on flood occurrence in Joneghan drainage basin,
Shahr-e – Koord, using a new method. In this respect, after preparing base maps
consisting of slope amount , geology , landuse , erodibility of geological
material , soil depth and drainage pattern , studies were performed in two
stages as follows: In the first stage, flood occurrence of hill slopes of each
sub- catchment was investigated. For doing so, work unit map was prepared using
slope and infiltration maps. Then in each sub-catchment, land use, erodibility
of geological materials and soil depth were overlaid with work unit map one by
one and dually. In the second stage, flood occurrence of drainage was
investigated as follows: First, longitudinal profile of main drainage of each
subcatchment was prepared using GIS. For investigation of flood occurrence of
drainages, slope and permeability of geological units were used. The results of
the first stage showed that permeability, slope, erodibility of geological
materials and soil depth have the greatest effect on flood occurrence,
respectively. Also based on this four – factor method, subcatchments were
divided into five flood occurrence classes as follow: low, low to medium,
medium, relatively high, and high. The results of the second stage showed that
drainage flood occurrence belongs to two classes of low to medium and medium.
By combining slope and drainage flood occurrence, it can be concluded that the
third subcatchment with medium flood occurrence is more susceptible to flood
relative to other subcatchments. With regard to the results of the present
study, it can be concluded that geology has high impact on flood occurrence and
permeability of geological materials decrease flood occurrence in the basin.