Matching the critical portion of the flow duration curve to minimise changes in modelled excess shear

Abstract

Hydrologic and hydraulic modeling in the USEPA Stormwater Management Model (SWMM) were used to examine the effectiveness of typical stormwater management practices in reducing the potential for stream erosion. Fifty-year continuous simulations were used to produce flow duration curves and stream erosion rates for a variety of critical shear stress values representative of both cohesive and non-cohesive sediments. An excess shear stress erosion potential index was used to evaluate changes in erosion between undeveloped conditions of a 10 hectare watershed and four variations of post-development stormwater control. Evaluation of flow duration curves showed that when development takes place, the duration of mid- to low-range discharges increase significantly, especially when detention practices are applied. In channels with low entrainment thresholds for bed and bank materials, e.g. sands and highly erodible clays, the significant increase of the duration of mid- to low-range discharges results in erosion potential index values greater than two regardless of the detention practices used. Overcontrol detention resulted in erosion potential index values of less than one, indicating a loss of erosion potential for bed materials such as most gravels (d(s) > 6 mm) and resistant clays that have critical shear stress values greater than four Pa.

Model application to assess effects of urbanisation and distributed flow controls on erosion potential and baseflow hydraulic habitat

“…Rohrer and Roesner 2006). Usually, in such models low-impact distributed flow controls are lumped together in large devices, and conventional devices such as ponds are used to represent low-impact devices approximately (e.g.…”

“…The 2-year return period flow rate is often used to indicate stream morphology effects (Leopold 1994, Roesner et al 2001. Considering that erosion is related to the duration of high flows as well as magnitude (MacRae 1997), other metrics have been used such as the duration of flows above a critical threshold (James 1995, Guther et al 1996, Rohrer and Roesner 2006 or bedload-transporting capacity integrated over a design storm event (MacRae 1997, Bledsoe et al 2007). Mecklenburg and Ward (2002) extended the latter approach to include a range of design events and their associated probability of occurrence.…”

Development of group method of data handling based on genetic algorithm to predict incipient motion in rigid rectangular storm water channel

“…Therefore, it is crucial to fully understand the de nition of \initial velocity" in designing urban drainage systems. It can be stated that generally the initial velocity occurs when the ow around the particle is more powerful than the resistance force of the particle weight [2]. So, \incipient motion" occurs when the calculated shear stress is greater than the critical shear stress of the bed substances in the channel.…”

“…Evaluating the ow conditions that produce incip-ient motion of coarse river-bed material dates back to several decades [2][3][4][5]. In the subject area of determining a constant velocity in order to consider self-cleansing within a channel, many researchers have tried to present a shear stress or velocity threshold to prevent sedimentation.…”

Comprehensive Management and Modeling of Water Quantities: Utilizing an Existing Watershed Model for Comprehensive Water Management and Planning, and Optimal Design of Outlet Control Structures for Ecological Detention Ponds

“…Previous work has evaluated the performance, ecological impact (Nehrke and Roesner 2002;Nehrke and Roesner 2004), and erosion potential (Rohrer and Roesner 2006;Pomeroy et al 2008) resulting from urban storm-water systems by comparing the post-development flow frequency curve to the pre-development curve; however, these studies were used for performance evaluation rather than design strategies. Flow frequency curves have also been suggested as a basis for the design of bioretention facilities (Palhegyi 2010a;…”