Determination of Form Friction Factor

Afzalimehr, Hossein; Singh, Vijay P.; Najafabadi, Elham Fazel

doi:10.1061/(asce)he.1943-5584.0000175

Cited by 17 publications

(7 citation statements)

References 27 publications

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“…Figure 3 indicates the velocity profiles at several locations in the channel to determine in what range the stream has been developed. Therefore, viscosity and boundary layer do not affect the velocity profiles, and hence the flow in x = 1049 cm is fully developed [29]. The z parameter is the distance from the bed to the location of velocity measured at any point.…”

Section: Channels and Tools Usedmentioning

confidence: 99%

Experimental Design of Nature-Based-Solution Considering the Interactions between Submerged Vegetation and Pile Group on the Structure of the River Flow on Sand Beds

Miyab

Fazloula

Heidarpour

et al. 2022

Water

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Designing correct engineering infrastructures to reduce land degradation processes and considering natural elements to achieve this goal are key to correctly managing potential natural hazards affecting human activities and natural ecosystems. This research investigated the scour depth and velocity vectors around bridge piles with and without upstream vegetation protection. A Doppler velocity meter was used to measure velocity components in a channel 90 cm wide, 16 m long, and 60 cm high. Variable parameters were the number of bridge piles, the height, density, and width of vegetation upstream, as well as the distance between bridge piles. Using a triple pile group with a distance between piles of 10 cm and overall vegetation across the channel, the depth of the scour hole upstream of the first pile decreased by 40% compared to the single pile with no vegetation. This result shows the significant impact of using vegetation and pile groups to reduce scour around piles. Lower vertical velocity gradients, more consistent velocity vectors, reducing the downstream flow range, and restraining horseshoe vortexes and wake vortices were observed in utilizing vegetation. We confirmed that vegetation is an essential factor in changing the flow, transportation of sediment, and conserving ecological services in rivers.

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Section: Channels and Tools Usedmentioning

confidence: 99%

Experimental Design of Nature-Based-Solution Considering the Interactions between Submerged Vegetation and Pile Group on the Structure of the River Flow on Sand Beds

Miyab

Fazloula

Heidarpour

et al. 2022

Water

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“…The total friction factor f is traditionally partitioned between the grain resistance f′ and form resistance f″ (Afzalimehr et al, 2010;Yalin, 1977) where the latter is generated by energy losses associated with irregularities in the shape of the channel. Here a somewhat different approach is taken as the friction includes both the vegetative flow resistance f‴ as well as the resistance of the channel boundary.…”

Section: Flow Resistancementioning

confidence: 99%

Quantifying Fluid Retention Due to Natural Vegetation in a Forest Floodplain Analogue Using the Aggregated Dead Zone (ADZ) Dilution Approach

Carling

Leyland

Kleinhans

et al. 2020

Water Resources Research

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Fluid retention and flow resistance due to natural vegetation remain poorly understood despite the importance of understanding these for flow routing and floodplain revegetation projects. Experiments were undertaken in a shallow earthen channel containing a natural cover of small trees, herbaceous plants, and leaf litter, which were sequentially removed and subjected to a range of flows. A dilution monitoring approach within the Aggregated Dead Zone framework was applied to a series of floodplain vegetated flows, yielding information on bulk flow parameters including tracer dispersion, fluid retention, and flow resistance at the reach scale. The primary response of flow to vegetation removal was a small increase in bulk velocity, with depth and wetted width decreasing only slightly. Reach mean travel time and the advective time delay decreased by about a factor of 2 with the removal of herbs, grass, and leaf litter, leaving only trees. Removing the trees, leaving a bare earthen channel, only slightly decreased travel times. Flow resistance and retention exhibited large values for low discharge and converged on a constant low value for relatively high discharges. It is concluded that flow resistance during low flow is higher than in a high flow with the same vegetation. Consequently, sparse vegetation has a prominent effect on hydraulic retention compared with an unvegetated channel at low discharges but this becomes negligible during high discharges as momentum increasingly dominates the flow. This outcome casts doubt on the efficacy of scrubby vegetation to impede higher-velocity floodplain flows, showing need for field-scale determination of integral floodplain resistance.

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“…The significance of each resistance type depends on the characteristics of the river, with fS dominating in gravel-bed rivers and fF prevailing in sand-bed rivers. Numerous studies have focused on quantifying bed shear stress induced by grain and form resistance separately (Afzalimehr et al, 2010;Einstein and Barbarossa, 1952;Garcia and Parker, 1993;Okhravi and Gohari, 2020;van Rijn, 1984;Wright and Parker, 2004;Yang et al, 2005). Venditti (2013) categorized methods for separating grain and form resistance into two general types.…”

Section: Introductionmentioning

confidence: 99%

Flow resistance at lowland and mountainous rivers

Okhravi,

Alemi,

Afzalimehr

et al. 2023

Journal of Hydrology and Hydromechanics

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This study initially examines the various sources of flow resistance in sand-bed (lowland) and gravel-bed (mountainous) rivers along with the limitations of traditional estimation methods. The nondimensional hydraulic geometry approach, relating dimensionless flow discharge (q *) to the Darcy-Weisbach friction factor (f), has demonstrated good performance for both river types, covering shallow to moderately deep flows. However, accuracy in estimating f is affected by simplifications like assuming uniform and deep flow, neglecting bed load transport and vegetation effects, which require further evaluation. To address these issues, the proposed method is evaluated using data from four sand-bed rivers in Slovakia (with vegetation), and three gravel-bed rivers in Iran (dominated by cobbles and boulders). Bedforms prove to be significant resistance sources in all studied rivers. The approach yields separate predictors for each river type, showing a satisfactory agreement between observed and calculated values within a maximum deviation of ±20% error bands. These predictors are further validated using field data and established equations from rivers with similar physiographic characteristics. Results indicate the method performs well in predicting flow resistance in sand-bed rivers, slightly overestimating overall (+40%). It effectively captures riverbed features and vegetation influence under small-scale roughness conditions. However, the predictor’s validity for gravel-bed rivers is somewhat limited due to high variability in water-surface profiles, making it challenging to accurately capture flow dynamics under large-scale roughness conditions. Addressing complex characteristics of gravel-bed riverbeds, including boulders and local energy extraction, is crucial for improving the estimation of water-surface profile variations and flow resistance using the hydraulic geometry approach.

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Determination of Form Friction Factor

Cited by 17 publications

References 27 publications

Experimental Design of Nature-Based-Solution Considering the Interactions between Submerged Vegetation and Pile Group on the Structure of the River Flow on Sand Beds

Experimental Design of Nature-Based-Solution Considering the Interactions between Submerged Vegetation and Pile Group on the Structure of the River Flow on Sand Beds

Quantifying Fluid Retention Due to Natural Vegetation in a Forest Floodplain Analogue Using the Aggregated Dead Zone (ADZ) Dilution Approach

Flow resistance at lowland and mountainous rivers

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