Kheyrrud originates from 2155 m elevations of mount Kalamlu and area of its drainage basin is more than 130 km2. Width of Alluvial fan for Kheyrrud is about 2-2.5 km. This river reaches to beach plain in Kheyrrud Kenar. Length of Kheyrrud is about 3 km in Caspian beach flood. Kheyrrud cuts Noshahr-Ruyan coastal road in km: 12. Gradient of Kheyrrud from mountain (where it originates) to southern Najjardeh is 17/1000 and from southern Najjardeh to margin of Caspian Sea is 14/1000. Local base level (LBL) of Kheyrrud is -22 m in area of city. There is not Hydrography station in river path.
Morphology: Path of Kheyrrud is narrow valley in its mountainous region. Path of this river has a river valley pattern in area of Kheyrrud city. Kheyrrud has several meanders and index of meander for this river is mean.
There are 2 groups of river terraces in beach plain for Kheyrrud:
- H1 (River terraces with down surface level): Boundary of 20-year floodwater (Mean height: 2 m)
- H2 (River terraces with high surface level): Boundary of 50 or 100-year floodwater (mean height: 5.5 m)
Materials of terraces are coarse-grained in the upstream of river and gradually more fine-grained they appear the farther away they are from foot hills (in size of gravel & sand with thin layers of Loess).
Walls of terraces have been formed from without cohesion (unconsolidated and slumping) alluviums (Recession rate of terraces: High).
Vegetation on surface of H2 is compact, but active flood plain is without vegetation.
Human interference in natural environment of Kheyrrud- land use changes:
- Construction in flood plain and on surface of H2 for Kheyrrud
- Development of padi soils on surface of terraces for 20-year floodwater
- Uncontrolled extraction of sand and gravel
- Accumulate of wastes and structural rubbishes in around of river
- Construction of available roads in active or seasonal flood plain
Characteristic of flood plain for Kheyrrud:
- Width of active flood plain: more than 60 m
- Width of seasonal flood plain: 20-35 m
- Width of alternative flood plain: 40-50 m
History of flood in Kheyrrud: The active, seasonal and alternative flood plains are observed in this river (Flood risk of Kheyrrud: 2).
The mainly floods happened in years of 1347 & 1353. Two relatively large-scale floods happened in years of 1381 & 1383. The floodwaters of Kheyrrud have not been had any victims.
Floodwater Velocity of Kheyrrud and its devastative potential (in mountainous region) is too high. The devastative potential and flow height for this river is decreased when it reaches to Caspian beach plain.
Vulnerable area of Kheyrrud: This area lies between 1.6 km of southern Kheyrrud and 400 m of northern Kheyrrud city (length: 2 km).
Main damage: Erosion and destruction of walls in concave parts of meanders
Mitigation plans of flood damages:
- Usage of protect pile method (accumulating of large rock blocks: Armor) in order to protection of agronomy lands on terraces from erosion
- Exact determination of flood plains with different return periods and product of large scale land use maps
- Determination of areas with high erosion risk