Quasi‐equilibrium conditions of urban gravel‐bed stream channels in southern Ontario, Canada

Abstract

Urban gravel‐bed stream channels in southern Ontario, Canada identified to be in a state of quasi‐equilibrium have been studied over the past 15 years and compared against rural gravel bed stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1‐year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in bed material supply appears to be off‐set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi‐equilibrium conditions as bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd.

Development of Regional Curves for Hydrologic Landscape Regions (HLR) in the Contiguous United States

“…However, not all HLRs with lower numbers of sites produced poorer fits (e.g., HLRs 1,3,15,and 19). The higher levels of variability associated with bankfull parameters is possibly linked to landscape factors such as the number and location of reservoirs upgradient in the watershed (Deitch et al, 2013), level of irrigation or water withdrawal within the watershed (Kendy and Bredehoeft, 2006;Caskey et al, 2014), reliance or lack thereof on snowmelt (USGS, 2005;Miller and Piechota, 2011), type of streamside vegetation (Hession et al, 2003), and degree of urbanization (Doll et al, 2002;Cianfrani et al, 2006;Annable et al, 2010). These factors may have influenced assessed streams unequally within and across these arid and semiarid HLRs, more so than the humid and subhumid HLRs.…”

Enlargement and evolution of a semi‐alluvial creek in response to urbanization

“…This model has been used to help interpret channel responses to urbanization whether through incision or channel widening (Henshaw and Booth, 2000;Hardison et al, 2009) even while it has become clear that it may not apply equally in all contexts Booth and Fischenich, 2015). If floodplain connectedness can be maintained, incision may be avoided, thereby averting the initiation of the cycle entirely (Hardison et al, 2009;Annable et al, 2012). If floodplain connectedness can be maintained, incision may be avoided, thereby averting the initiation of the cycle entirely (Hardison et al, 2009;Annable et al, 2012).…”

“…Available evidence suggests that an initial aggradational response of approximately 15 years due to increased sediment loads (Wolman and Schick, 1967) is followed by channel enlargement over anywhere from 5 to over 50 years posturbanization (Chin, 2006), though a wide range of adjustment periods have been observed (Henshaw and Booth, 2000;Hardison et al, 2009;Annable et al, 2012). Available evidence suggests that an initial aggradational response of approximately 15 years due to increased sediment loads (Wolman and Schick, 1967) is followed by channel enlargement over anywhere from 5 to over 50 years posturbanization (Chin, 2006), though a wide range of adjustment periods have been observed (Henshaw and Booth, 2000;Hardison et al, 2009;Annable et al, 2012).…”

Bankfull Hydraulic Geometry Relationships for the Inner and Outer Bluegrass Regions of Kentucky

“…Both Cianfrani et al [55] and Doll et al [56] found that urbanization increased bankfull channel width as compared to rural streams in the Piedmont region of the U.S. Contrary, Annable et al [57] found that urbanization did not result in significant channel enlargement for streams in Ontario, Canada. In this study, no trends between percent imperviousness and bankfull width were found for the Outer Bluegrass (Figure 10), so it is likely that the level of urbanization is not the controlling factor for bankfull width.…”