Evaluating the Impact of Sediment Seeding Strategies in Pool-Riffle Restoration: Experimental Insights Into Hydraulic and Spawning Habitat Performance

Abstract

Restoring streams by feeding sediment from a single location is cost-effective, allowing natural sediment distribution. Alternatively, placing sediment in predetermined patterns requires more planning but may provide controlled improvements to flow and habitat. However, the effectiveness of specific seeding patterns in achieving restoration goals remains unexamined. This study uses a flume model of a scaled fixed-bed pool-riffle channel and a 2D hydraulic model to investigate the impact of seeding patterns on sediment retention, hydraulic performance, and spawning habitat suitability within a restored pool-riffle channel. We tested three seeding patterns—Head-Seed (HS), Tail-Seed (TS), and Full-Seed (FS)—under flow conditions ranging from Qspawning to Q100. Results reveal that seeding patterns influence sediment retention in pool-riffle sequences. While 95% of seeded sediment remained in the channel during Qspawning across all patterns, the FS pattern showed a greater sensitivity to increased flow, with a logarithmic decline in cover fraction and higher sediment export compared to HS and TS strategies. High shear stress zones, promoting full sediment mobility, appeared at the pool-heads with steep bed slopes, while deposition occurred in low shear stress zones at pool-tails. Minor changes in bed elevations from alluvial cover development did not alter shear stress distribution, highlighting the dominance of channel design over initial seeding conditions. Despite FS pattern provided more suitable spawning area (37%) compared to TS (22%) and HS (13%), its higher sediment export under elevated flows raises concerns about downstream sedimentation and long-term habitat sustainability. This study emphasizes the importance of balancing short-term habitat gains with long-term stability.