2hezar-3hezar & Tirum large rivers create a large alluvial fan in initial of Caspian beach plain that its width is more than 11 km2. Eastern boundary of this alluvial fan is Cheshmeh Gileh River (Tonekabon County) and its western boundary is Shirud (Tirum) River. Length of Shirud River is more than 11 km in beach plain and its gradient changes 9/1000 to 12/1000. Local base level (LBL) of Tirum River is -24 m above the sea level. This river cuts Ramsar- Tonekabon coastal road in km: 17+100. Area of drainage basin for Tirum is about 80 km2 and there is not Hydrography station in its path.
Morphology: Tirum River has direct flow, but several meanders is observed in its path. Index of Sinusity for Shirud River is low to mean.
Morphology of Shirud is divided into 2 parts:
1) Morphology of Shirud to 2 km from buildings: There are 2 groups of river terraces in this distance:
- H1 (River terraces with down surface level): Height: 1-2.5 m
- H2 (River terraces with high surface level): Height: 3-6 m
Recognition of these 2 groups of river terraces (especially H1) is too difficult. H2 has been eroded less than H1, so it is a site for construction, paddy fields and vegetation now.
In this part, materials of terraces mainly consist boulders and coarse-grained materials that are not enough cohesive so they tend to slumping (high erodibility of walls and high velocity of recession of terraces and quick widening of river).
In this area:
- Width of Shirud River: more than 250 m
- Minimum width of stream-bed of river: 15-50 m
- Maximum width of active and alternative flood plains: 130 m
2) Morphology of Shirud at 2 km of Shirud: Separation of H1 and H2 is too difficult in this area. Feature of river consists a minor stream-bed and it has been surrounded by heights from two sides, so they are not recognizable.
Human interference in natural environment - land use changes:
- Construction of buildings and available roads in active flood plain
- High extraction of sand and gravel from stream-bed of river
- Accumulate of structural rubbishes and wastes in around of river
History of flood in Shirud: Floodwater of Shirud River happened thrice in 1379; its first flood was tremendous. Floodwaters of 1340 and 1356 (twice each year) were from devastative floodwaters. Floodwater of 1374 for Shirud was too hideous. Nowadays stream flood of Shirud causes immersion and it imports very damages to agronomy lands.
Vulnerable area of Shirud: This area lies between 2 km of southern Shirud and 200 m of northern Shirud.
Mitigation plans of flood hazard: There is no distinct plan in order to mitigation of flood hazard for this river.
- Accomplishment of river dredging; but extraction of stream-bed materials is too much by this work (is causes accelerated scour and widening of river)
- Accumulating of alluvial materials in around of river in order to separation of floodwater from agronomy lands (is not a suitable method in order to protection)
- Recognition of damaged buildings in area of Shirud
- Suggestion of exact studies in order to recognition of areas with high erosion risk (especially in urban area) and also suggestion of suitable executive methods for theirs protection