The sinuosity index (also called sinuosity or sinuosity coefficient) is a dimensionless metric that quantifies the degree of meandering or curvature in a channel, such as a river or stream. It is calculated as the ratio of the actual path length of the channel (curvilinear length) to the straight-line distance (Euclidean distance) between two endpoints, commonly the source and mouth of a river.​Sinuosity Index (SI)=Channel lengthStraight-line distance (downvalley or valley length)Sinuosity Index (SI)=Straight-line distance (downvalley or valley length)Channel length

• A sinuosity index of 1 means the channel is perfectly straight.
• Values greater than 1 indicate increasingly winding, twisting, or meandering paths.

Classification by Sinuosity Index

• SI < 1.05: almost straight
• 1.05 ≤ SI < 1.25: winding
• 1.25 ≤ SI < 1.5: twisty
• SI ≥ 1.5: meandering​

Geographical and Hydrological Importance

• The sinuosity index helps in understanding river dynamics, sediment transport, flood management, and landscape evolution.
• It is affected by factors such as river slope, sediment type, discharge, structural geology, and vegetation. Sinuosity often increases as slope decreases, and meandering is typically associated with mature river phases.​

In summary, the sinuosity index is a widely used indicator in geomorphology and hydrology to compare the straightness or curviness of fluvial channels and other natural or artificial paths.

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River Stages:Middle Course of the River – Meanders & Ox-bow Lakes