Bed-material entrainment in a mountain river affected by hydropeaking

Area of Science:

• Environmental Science
• Hydrology
• Geomorphology

Background:

• Hydropeaking, caused by artificial flow fluctuations, significantly alters river hydro-sedimentary dynamics.
• These alterations impact sediment entrainment and transport processes in riverbeds.

Purpose of the Study:

• To investigate the initiation of sediment particle motion in a Pyrenean river subjected to frequent hydropeaking.
• To assess the effectiveness of five entrainment criteria in predicting grain motion at a section scale.

Main Methods:

• Field study in four sections of a Pyrenean gravel-to-cobble bed river.
• Application and validation of five theoretical particle entrainment criteria using tracer data.
• Analysis of hydro-sedimentary dynamics and sediment transport over a 17 km segment.

Main Results:

• Hydropeaking primarily affects the furthest downstream section (17 km), entraining finer bed fractions up to coarse gravels (≈ 30 mm).
• Sediment supply from tributaries, bed slope, and surface layer structure control downstream variations in particle motion.
• Hydropeaking induces partial, size-selective transport, winnowing sand and small gravel downstream, leading to increased armouring and fine sediment depletion.

Conclusions:

• Hydropeaking significantly influences sediment transport patterns, with downstream effects being more pronounced.
• Riverbed characteristics and sediment supply interact with hydropeaking to create variable sediment mobility conditions.
• The study highlights the ecological implications of hydropeaking, including altered riverbed composition and potential habitat degradation.