A Simple and Accessible Method for Countrywide Assessment of Stream and River Sinuosity Indicates That Nearly Half of Estonian Rivers and Streams Are Straightened

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ABSTRACT Riverine corridors—streams, rivers, and riparian areas—have been modified in multiple ways and at a large scale during the second half of the last century. One of the major impacts is riverine straightening, which has reduced connectivity and habitat quality in these biodiverse ecosystems. We developed a simple and easily repeatable GIS analysis for assessing the straightening proportion of river channels on a country‐wide scale. The method is applied to Estonian rivers, which have gone through extensive anthropogenic modifications rather recently, during the second half of the twentieth century. Streams and rivers were split into segments and for each segment the sinuosity index was calculated. From 14,417 km of streams and rivers included in the analysis, 42% was estimated to be straightened. Cumulative probability for sinuosity was lowest for the smallest river length classes and highest for rivers 40+ km long. The shorter the stream or river, the larger proportion of its whole length is straightened. The wide reach of anthropogenic modification of streams and rivers all over Estonia makes protecting and restoring them challenging, as there are many interested parties working in the same landscape: forestry, agriculture and urban development. We give recommendations for starting large scale restoration and enhancing legislative riverine ecosystem protection using nature‐based solutions at nature conservation areas. At the same time, work should be ongoing to find solutions outside of conservation areas to diversify and connect these long ecosystems that sustain also functioning ecosystem at wider landscape. The tool developed here can be used as a communication tool for awareness‐raising about the anthropogenic threats to rivers, and for initiating large‐scale restoration programs.

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