Shawn P. Clark

The 2009 flood event in the Red River Basin: Causes, assessment and damages

The Red River once again experienced significant flooding in spring 2009 due to high antecedent soil moisture from the previous fall and a deep snowpack and deep frost penetration. The peak stage at Fargo, North Dakota, broke the previous record set in 1897, and the peak stage at Grand Forks, ND, was the third largest in its 126 years of record. The computed natural river crest in Winnipeg, Manitoba, was the second largest experienced since official records began in 1912, and the unregulated flow volume at Selkirk, Manitoba, was the highest on record since 1852. Beyond its statistical significance, the 2009 Red River flood was unique due to the magnitude and frequency of ice-related issues throughout the duration of the flood. Ice jams developed within Winnipeg and near the community of Lockport, and went through phases of formation and release that made it difficult to forecast water levels. The presence of ice also affected operation of the Floodway Inlet Control Structure, and a small ice jam even developed within the Floodway itself. Despite the magnitude of the flood event and the challenges associated with the ice conditions, the extensive level of flood protection along the Red River generally reduced the level of inconvenience and flood damage. The exception was the area downstream of the City of Selkirk that underwent flooding of a magnitude that had not been experienced for a century and a half. A large number of homes along this reach of the river were damaged beyond repair and were subject to a government buyout after the flood.

Flow characteristics within the recirculation region of three-dimensional turbulent offset jet

ABSTRACT The present study investigates the flow characteristics within the recirculation region of three-dimensional offset jets using a particle image velocimetry technique. Measurements were performed for four nozzle offset height ratios of 0, 2, 4 and 8. The discharged jet entrained the ambient fluid as depicted by streamlines superimposed on the mean velocity contours. Analysis of the flow field showed that the maximum streamwise mean velocity decay rate increased with increasing offset height ratio. Wall-normal spread rates of 0.066 and 0.016 were obtained for jets with offset height ratios of 0 and 2, respectively, and lateral spread rates of 0.116, 0.114 and 0.096 for jets with offset height ratios of 0, 2 and 4, respectively. The reattachment lengths of the jets increased with increasing offset height ratio. Profiles of the mean velocities, Reynolds stresses and some of the budget terms (specifically, production, diffusion and convective terms) of the turbulent kinetic energy have been investigated. It was observed that increasing the offset height ratio influenced the distribution of these quantities within the recirculation region. A two-point velocity correlation analysis was performed to analyse the flow structures within the recirculation region. The two-point correlation revealed some large-scale structures which were observed to increase in size as the offset height ratio increased. The two-point correlation analysis also revealed that the estimated integral length scales within the recirculation region of the flow increased with increasing offset height ratio.

Background to flood control measures in the Red and Assiniboine River Basins

The City of Winnipeg and southern Manitoba have a long history of flooding, with flood events being recorded soon after the region was settled in the early nineteenth century. A devastating flood on the Red River in 1950 resulted in some of the earliest benefit–cost analyses in Canada with respect to flooding, and justified the construction of major flood mitigation projects on the Red and Assiniboine Rivers in the 1960s and 1970s. These projects were primarily designed to reduce the risk to the City of Winnipeg. Other projects have been constructed outside of the Winnipeg area, which have reduced flood damages to towns, individual farmsteads and rural residences. The level of flood protection has been re-evaluated every time a new flood of record occurs, and this has resulted in significant upgrading of existing works and the addition of more communities with permanent flood protection. As a result of the flood protection system that has been developed in Manitoba over the last 60 years, the damage caused by floods has been significantly reduced over natural conditions. The purpose of this paper is to provide context to flooding in Manitoba with a consideration of how flooding, flood damage and the impact on citizens of Manitoba have been mitigated by permanent flood protection works.

Turbulent velocity distribution with dip phenomenon in conic open channels

ABSTRACT Conic open-channel flow as occurs in sub-drains, sewers, and culverts is computed by Mannings or Darcys resistance equations for the cross-sectional average velocity only. Yet, fish passage culvert design requires the cross-sectional velocity distribution, which is proposed in this paper based on two hypotheses: (i) centreline velocity distribution follows the conventional log-law with a cubic deduction near the water surface; (ii) cross-sectional velocity distribution is described by Guo and Juliens modified log-wake-law but neglecting the squared sine function. These hypotheses result in a novel and simple velocity distribution model without any fitting parameter. Its graphical interpretation for the elliptic, parabolic, and hyperbolic channels indicates reasonable velocity contours with dip phenomenon. Further, it agrees well with circular pipe data related to the average shear velocity, velocity-dip position, centreline and cross-sectional velocity distributions. A potential application includes fish passage culvert design by specifying a low velocity zone near the wall.

Experimental study of the flow structures of 3D turbulent offset jets

ABSTRACT Three-dimensional turbulent offset jets were investigated using a particle image velocimetry technique. Detailed measurements were performed for offset height ratios of 0, 2 and 4. The presence of backflow influenced the distribution of the mean velocity and Reynolds stresses. A two-point correlation analysis was used to investigate the spatial distribution of large-scale structures within the inner shear layer of the flow domain. The results revealed that large-scale structures dominate the inner layer of the self-similarity region. Proper orthogonal decomposition was performed on the fluctuating velocity field within the symmetry and lateral planes using the snapshot approach. Results from the reconstructed field provided insight into the contributions of the most energetic structures to the turbulence statistics. The energetic structures contributed more to the Reynolds shear stress and streamwise turbulence intensity, while contributing less to the wall-normal turbulence intensity.

Beyond average velocity: modelling velocity distributions in partially filled culverts to support fish passage guidelines

ABSTRACT An important consideration in managing a river basin is how to treat the many stream crossings within the basin. Historically, corrugated metal pipe (CMP) culverts have been commonly selected for stream crossings throughout the world. The associated reduction in cross-sectional flow area causes an increase in water velocity at the culvert, which may become a barrier to fish passage. In Canada, existing guidelines compare the swimming performance of fish that may use the culvert with the average velocity within the culvert at some design flow. It is known that a velocity distribution occurs within culverts, and it is hypothesized that fish may possess the ability to sense and locate preferential swimming paths within low-velocity zones in a culvert. To facilitate the design of culverts in a manner that may better consider fish swimming performance, this paper compares the results of empirical and numerical modelling of the velocity distribution within partially full CMP culverts at uniform depth. An additional simplified model to estimate the percentage of the cross-sectional area with a water velocity less than any reference velocity is presented. Finally, the concept of using two-dimensional velocity distributions in combination with fish preference data for water velocity and depth is presented.

Flow Characteristics beneath a Simulated Partial Ice Cover: Effects of Ice and Bed Roughness

AbstractAt the onset of winter in cold regions, border ice may form along the banks of a river and grow outward toward the center of the channel. This type of transient ice process is not well unde...

Roughness effect on turbulent flow structure beneath a simulated ice jam

ABSTRACT Detailed velocity measurements beneath a modelled ice jam with both smooth and rough surfaces were conducted using acoustic Doppler velocimetry and particle image velocimetry. The experiments were conducted at Reynolds numbers based on hydraulic diameter of 28,400 and 72,000. The topography of the mean flow field revealed acceleration and deceleration of the flow within the upper and lower toe sections of the modelled jam, respectively. The introduction of surface roughness increased flow blockage, thereby increasing the maximum streamwise mean velocity within the upper toe section. The estimated bed shear stress attained a maximum within the toe section, with roughness significantly increasing the values. Large vortical structures dominated the flow over the rough surface compared to the smooth case. The present results suggest the possibility of enhanced sediment transport beneath the modelled jam when both bed and ice jam were roughened.

Acoustic Doppler velocimeter measurements of a submerged three-dimensional offset jet flow over rough surfaces

ABSTRACT The flow characteristics of a submerged three-dimensional offset jet over transverse square ribs and gravel are experimentally investigated using an acoustic Doppler velocimeter. The pitch-to-height ratio of the ribs was varied to achieve d-type, intermediate, and k-type roughness. The Reynolds number based on the nozzle height and jet exit bulk velocity was 53,000. The mean flow properties and turbulent statistics are compared to those obtained over a smooth surface. Both decay and wall-normal spread rates were independent of surface roughness with estimated values of 0.66 ± 0.03 and 0.138 ± 0.01, respectively, with these values influenced by the presence of lateral confinement of the flow. The distribution of the mean flow, within the inner shear layer, revealed a dependence on surface roughness after reattachment. A representation of the Reynolds normal stresses within the symmetry and lateral planes revealed the highly anisotropic nature of the turbulence field of offset jets.

Morphodynamics of diversion channels in Northern Manitoba, Canada

The 2-Mile and 8-Mile diversion channels in Northern Manitoba help to maintain the efficiency of Manitoba Hydro’s hydroelectric generating stations located downstream on the lower Nelson River and also assist with flooding control on Lake Winnipeg. Erosion within the channels has been consistently monitored for several decades to better understand these processes to ensure the future performance of the channels. Morphodynamic studies in these channels are complicated due to the high variability of the bed and bank material, the effect of severe cold weather on the erodibility of the channel banks, and the effect of the surrounding lakes on the hydrodynamic conditions of these channels. The present study includes field measurements, experimental testing, and hydrodynamic and thermal numerical modelling to quantify morphological changes within the channels. Moreover, 30 years of monitoring data were analyzed to validate the results of the study. Simple graphs were presented to estimate average applied shear stress over the channel banks and beds based on results of the calibrated and validated hydrodynamic models. Moreover, the effects of wave action on the total applied shear stress were investigated within the 2-Mile Channel under different flow conditions. Comparison between historical cross-sectional survey and results of the numerical models and experiments showed that subaerial processes, mostly freeze–thaw, could be a major eroding factor.