Pools, channel form, and sediment storage in wood-restored streams: Potential effects on downstream reservoirs

Elosegi, A., et al., 2017. Geomorphology

Original research (primary data)
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Large wood (LW, or pieces of dead wood longer than 1 m and thicker than 10 cm in diameter) is a key element in forested streams, but its abundance has decreased worldwide as a result of snagging and clearing of riparian forests. Therefore, many restoration projects introduce LW into stream channels to enhance geomorphology, biotic communities, and ecosystem functioning. Because LW enhances the retention of organic matter and sediments, its restoration can reduce siltation in receiving reservoirs, although so far little information on this subject is available. We studied the effects of restoring the natural loading of LW in four streams in the Aiako Harria Natural Park (the Basque Country, Spain) in pool abundance, channel form, and storage of organic matter and sediments. In all reaches log jams induced the formation of new geomorphic features and changes in physical habitat, especially an increase in the number and size of pools and in the formation of gravel bars and organic deposits. The storage of organic matter increased 5- to 88-fold and streambed level rose 7 +/- 4 to 21 +/- 4 cm on average, resulting in the storage of 35.2 +/- 19.7 to 711 +/- 375 m(3) (733-1400 m3 ha(-1) y(-1)) of sediment per reach. Extrapolation of these results to the entire drainage basin suggests that basinwide restoration of LW loading would enhance the retention potential of stream channels by 66,817 +/- 27,804 m3 (1075 m(3) ha(-1) y(-1)) of sediment and by 361 t (5.32 T ha(-1) y(-1)) of organic matter, which represents 60% of the estimated annual inputs of sediments to the downstream Afiarbe Reservoir and almost twice as much as the annual input of organic matter to the entire river network. Therefore, basinwide restoration of LW loading is a potentially important tool to manage catchments that feed reservoirs, where retention of sediments and organic matter can be considered important ecosystem services as they reduce reservoir siltation.

Case studies

Basic information

  • Case ID: INT-098-1
  • Intervention type: Restoration
  • Intervention description:

    Restoring the loading of large wood into 4 streams: introducing logs and branches into stream channels, mimicking the type of structures commonly found in streams in the region

  • Landscape/sea scape ecosystem management: No
  • Climate change impacts Effect of Nbs on CCI Effect measures
    Reduced water quality  Positive stream bed elevation (indicator of sediment retention) total sediment retention, retention rate (m3 ha−1 y−1), retention efficiency
  • Approach implemented in the field: Yes
  • Specific location:

    Aiako Harria Natural Park (Basque Country, north Spain) in one first-order stream (Atseginsoro), two second-order streams (Malbazar and Latxe), and a fourth-order stream (Añarbe) that all flow into the Añarbe reservoir

  • Country: Spain
  • Habitat/Biome type: Streams, rivers, riparian |
  • Issue specific term: Not applicable


  • Notes on intervention effectivness: effectiveness compared by assessing sediment retention before and after intervention + monitoring change over time since restoration intervention began
  • Is the assessment original?: Yes
  • Broadtype of intervention considered: Not applicable
  • Compare effectivness?: No
  • Compared to the non-NBS approach: Not applicable
  • Report greenhouse gas mitigation?: No
  • Impacts on GHG: Not applicable
  • Assess outcomes of the intervention on natural ecosystems: No
  • Impacts for the ecosystem: Not reported
  • Ecosystem measures:
  • Assess outcomes of the intervention on people: No
  • Impacts for people: Not reported
  • People measures:
  • Considers economic costs: No
  • Economic appraisal conducted: No
  • Economic appraisal described:
  • Economic costs of alternative considered: No
  • Compared to an alternative: Not reported

Evaluation methodology

  • Type of data: Quantitative
  • Is it experimental: No
  • Experimental evalution done: Not applicable
  • Non-experimental evalution done: Empirical case study
  • Study is systematic: