Rill hydraulics on a semiarid hillslope, southern Arizona

Abstract

Seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at Walnut Gulch, Arizona. The rills, which are characterized by wide, shallow cross-sections and gravel-covered beds, have mean at-a-station hydraulic geometry exponents of b = 0.33, f = 0.34 and rn = 0.33. Although the differences between these values and typical values of b = 0.30, f = 0.40 and m = 0.30 for cropland rills are not statistically significant, they are thought to be real, as cropland rills often have more rectangular cross-sections and steeper sides than the rangeland rills under study. For rills formed in silty loamy soils, Govers developed an empirical relation between mean flow velocity and discharge. Emphasizing the generality of this relation, he suggested that it may be used as a simple means of routing runoff through rills. He also noted that this relation appeared to be unaffected by either slope or soil materials. The present data represent rills underlain by coarser and somewhat more varied gravel-rich soils. These data do not conform to Govers' relation, and a multiple regression analysis reveals that slope and soil materials, either directly or indirectly through bed roughness, exert almost as much influence on flow velocity as does discharge. Three alternative methods are developed for predicting flow velocity in the rills under study. All three methods give good results with the largest root mean square deviation being 3.115cms-'.

Hydraulic characteristics and sediment generation on slope erosion in the Three Gorges Reservoir Area, China

“…Foster et al (1984) concluded that the resistance coefficient was less than 0.5 at slope gradients of 1.7° to 5.16°. However, Abrahams et al (1996) studied rill hydraulics on a semiarid hillslope. They reported that, under the condition of slope gradients kept at 0.74° to 3.2°, the DarcyWeisbach friction coefficients ranged from 0.2 to 2.84 in wide shallow rills.…”

Effect of hydraulic parameters on sediment transport capacity in overland flow over erodible beds

“…However, Guy et al (1990) and Zhang et al (2009) found that the relationship between transport capacity and mean flow velocity was almost independent of slope. The possible reason for this contradiction is that under non-erodible beds, the mean flow velocity gradually increases with slope due to less variation in bed roughness (Foster et al, 1984;Abrahams et al, 1996;Gimenez and Govers, 2001;Zhang et al, 2009), while for erodible beds the mean flow velocity is almost independent of slope effect because bed morphology and roughness is dependent on both discharge and slope (Govers, 1992;Nearing et al, 1997Nearing et al, , 1999Takken et al, 1998;Gimenez and Govers, 2001). The impact of slope gradient on mean flow velocity was also found non-significant for the flow conditions that were used to conduct the current erodible bed flume experiments (Ali et al, 2012).…”

Rill Hydraulics - An Experimental Study on Gully Basin in Lateritic Upland of Paschim Medinipur, West Bengal, India

“…Gimenez and Govers (2001) also showed the slope independence of rill flow velocity by identifying feedback mechanism between rill bed roughness and flow hydraulics. On the contrary, the mean flow velocities appeared to depend on both flow discharge and slope of the rill (Foster et al, 1984;Abrahams & Li, 1996). Yet, for situations where a rill is able to adjust freely its geometry to the flow condition impact of slope on flow velocity becomes insignificant (Takken & Govers, 1998).…”