Blockage Probability Modeling of Large Wood at Reservoir Spillways With Piers

Abstract

Large wood increases the morphological and hydraulic complexity of rivers, yet it may block and modify the flood discharge capacity of hydraulic structures. To assess the related risk, blockage probability estimation for hydraulic structures such as reservoir spillways is needed. This work presents unstudied parameters for blockage of large wood with a reservoir‐type approach flow, where the inflow velocity has a negligible magnitude. Experiments were conducted in a channel with an ogee crested spillway equipped with piers, representing a commonly used hydraulic structure. Artificial stems were used to systematically evaluate the influence of stem length and stem draft on the blocking process. Different hydraulic conditions were evaluated by changing the water level in the reservoir. The head at the spillway crest with respect to stem draft was found to be a key parameter for blockage probability estimation at a spillway. Additionally, stem length was related to the bay width in the estimation of blockage. Larger heads tend to reduce the blocking probability of large wood, for a given stem draft, while increasing the relative stem length tends to increase the blocking probability. A logistic regression model is provided to estimate large wood blockage probability at ogee crested spillways with piers. Finally, recommendations for engineering practice are presented.

Small-Scale Modeling of Flexible Barriers. II: Interactions with Large Wood

“…In line with the comprehensive analysis of Furlan et al (2019Furlan et al ( , 2020Furlan et al ( , 2021 who studied the initiation of log trapping at reservoir dam spillways, we aimed at estimating the probability of each log to be trapped when transported alone. Following the recommendation from Furlan et al (2020), each log was introduced n supplied ¼ 30 times in the flume for each discharge, slope, and bottom clearance.…”

“…Several recent works have focused on the effects of LW on flow levels at rigid structures as dam reservoir spillways (Furlan et al 2019(Furlan et al , 2020(Furlan et al , 2021Vaughn et al 2021;Bénet et al 2021Bénet et al , 2022, slit and slot dams (Piton et al 2020), as well as, at racks made of piles (Shibuya et al 2010;Schmocker and Hager 2013;Horiguchi et al 2015;Schalko et al 2018Schalko et al , 2019aSchalko 2020). Schalko et al (2018) notably performed a thorough analysis of the head losses related to LW accumulations.…”

Partial Driftwood Rack at Gated Ogee Crest: Trapping Rate and Discharge Efficiency

“…Several studies proposed structures or countermeasures to avoid an interference of driftwood with the flow section fixing the undisturbed rating curve. Alternatively, the effect of driftwood on the rating curve or its trapping rate (or blocking probability) were described (Hartung and Knauss 1976;Perham 1986;Johansson and Cederström 1995;USACE 1987USACE , 1997Le Lay and Moulin 2007;Hartlieb 2012;Pfister et al 2013;Yang 2013;Schmocker 2017;STK 2017;Walker and Shinbein 2020;Schalko et al 2018;Lassus et al 2019;Furlan et al 2019Furlan et al , 2020Furlan et al , 2021Piton et al 2020).…”

“…Two studies seem particularly interesting in the present context: • Godtland and Tesaker (1994) conducted model tests considering a linear ogee weir with and without piers. Single trees typically passed the crest without piers if the head exceeded 85% of the trunk diameter (Pfister et al 2013;Furlan et al 2021). With piers, the bay width b had to be larger than 80% of the maximum (subscript M) trunk length L M to induce passage of most trees (USACE 1997).…”

Modeling Large Wood Transport in Semi-Congested Regime with Multiple Entry Points

“…Nonetheless, a fully Eulerian model presents some limitations that need to be carefully addressed regarding both the transport and the accumulation mechanism. Regarding accumulation, the arrest mechanism should be considered with care since it cannot be modeled directly on the physics of the phenomenon but is more likely to follow a probabilistic approach as highlighted by laboratory analysis for bridge [34], check dams [35], or dam accumulations [36].…”