Placed Rock as Protection against Erosion by Flow down Steep Slopes

Field and model tests of riprap on steep slopes exposed to overtopping

“…The critical stone-related Froude number F s,c for placed riprap is plotted as a function of slope in Figure 2(b) using data reported by Larsen et al (1986), Dornack (2001), Peirson et al (2008), Lia et al (2013) and Hiller et al (2017). reveals that F s,c scatters more for placed riprap than for dumped and that placed riprap is more stable, especially at steep slopes.…”

“…A possible explanation for the variability of F s,c in Figure 2(b) is the difference in packing factors, which varied from P c = 0.53 (Hiller et al 2017) to P c = 0.65 (Larsen et al 1986), P c = 0.80 (Dornack 2001) and P c = 0.94 (Peirson et al 2008). The different P c values may be related to the shape of the stones used, in addition to the quality of the packing.…”

“…For dumped riprap, failure is usually considered when the underlying filter layer is exposed to the flow due to the erosion of the riprap (e.g. Linford and Saunders 1967;Abt and Johnson 1991;Robinson et al 1998;Peirson et al 2008). If the same definition is applied for a singlelayer placed riprap, this would mean that erosion of a single stone would correspond to riprap failure because the filter will be exposed at this particular location.…”

“…A recent summary of design relationships for dumped riprap exposed to overtopping, including data of corresponding stability studies, has been presented by Abt et al (2013). These data are plotted in Figure 2(a) along with data from Godtland (1989), Larsen et al (1986), Peirson et al (2008) and Hiller et al (2017) showing the critical stone-related Froude number F s,c as a function of the slope S. The figure also contains the results of the model tests reported by Lia et al (2013), but the data from their field tests are not included due to the reasons discussed below. In order to visualise the variability of the stone size d used in the corresponding studies, the marker size is proportional to this parameter in Figure 2(a,b).…”

“…There exist two general riprap types, dumped and placed, which are constructed by either dumping the riprap elements or placing them in an interlocking pattern. The construction of placed riprap is more cost-and labour-intensive than simply dumping elements (Peirson et al 2008), but placed riprap can withstand higher discharges than dumped riprap constructed with the same stone size (Larsen et al 1986;Peirson et al 2008;Hiller et al 2017), especially on steep slopes (Dornack 2001). …”