Reducing of Bend Scour by Setting Spurs in a Curved Channel

In Taiwan, the rivers not only are fast-flowing with high discharge, but they badly erode their beds during the typhoon seasons. In addition, erosion on the concave bank in a meandering channel is the primary cause of levee break. Therefore, the study conducted a down-scale experiment on erosion induced by oblique flow in a laboratory. It was similar to number 27–34 cross sections of the Fengshan river of Hsinchu County, Taiwan. The region was chosen because there are some special attacking angles of water flow and historical precedents of levee break. The study adopted the discharges of return periods of 10 and 20 years and measured the flow field by laser doppler velocimetry (LDV). Then the protective effects with different spur types were examined. The results indicate that increasing velocity induces side erosion when the flow impacts with the adjacent angle on the concave bank. However, the decreasing of velocity causes deposition of sediment on the concave bank. Furthermore, based on the vertical velocity profile of water flow, a higher flow rate is measured in the downstream on the concave bank. After the spurs are installed, the velocity at the spurs in the downstream is reduced, and the cross section with the larger velocity is moved to upstream. In addition, after setting the spurs, the reduction rates in volume of scour are 7.97% of a 10 year return period and 4.65% of a 20 year return period, respectively. That demonstrates the scour is effectively reduced as long as the spurs are set. Although the erosion mitigation rate and protection effect are decreased when the velocity is high, there is still a good protection effect at the bank. The setting of spurs has the following effects: First, the maximum scour depth generates in the front spur, while the maximum scour position keeps away from the bank. Then, the overall flow rate can be reduced to approximately 35%–40% comparing with the original flow field. Lastly, the spur on the slope of 1/30 degrees demonstrated the best function of stretching the distance from the embankment.

Mississippi River Adaptive Hydraulics model development and evaluation, Commerce to New Madrid, Missouri, Reach

A numerical, two-dimensional hydrodynamic model of the Mississippi River, from Thebes, IL, to Tiptonville, TN (128 miles/206 km), was developed using the Adaptive Hydraulics model. The study objective assessed current patterns and flow distributions and their possible impacts on navigation due to Birds Point New Madrid Floodway (BPNMF) operations and the Len Small (LS) levee break. The model was calibrated to stage, discharge, and velocity data for the 2011, 2015–2016, and 2017 floods. The calibrated model was used to run four scenarios, with the BPNMF and the LS breach alternately active/open and inactive/closed. Effects from the LS breach being open are increased river velocities upstream of the breach, decreased velocities from the breach to Thompson Landing, no effects on velocity below the confluence, and cross-current velocities greater than 3.28 ft/s (1.0 m/s) within 1186.8 ft (60 m) of the bankline revetment. Effects from BPNMF operation are increased river velocities above the confluence, decreased velocities from the BPNMF upper inflow crevasse (Upper Fuseplug) to New Madrid, cross-current velocities greater than 1.5 ft/s (0.5 m/s) only near the right bank where flow re-enters the river from the BPNMF lower inflow/outflow crevasse Number 2 (Lower Fuseplug) and St. Johns Bayou.

An integrated modeling approach to predict flooding on urban basin

Correct prediction of flood extents in urban catchments has become a challenging issue. The traditional urban drainage models that consider only the sewerage-network are able to simulate the drainage system correctly until there is no overflow from the network inlet or manhole. When such overflows exist due to insufficient drainage capacity of downstream pipes or channels, it becomes difficult to reproduce the actual flood extents using these traditional one-phase simulation techniques. On the other hand, the traditional 2D models that simulate the surface flooding resulting from rainfall and/or levee break do not consider the sewerage network. As a result, the correct flooding situation is rarely addressed from those available traditional 1D and 2D models. This paper presents an integrated model that simultaneously simulates the sewerage network, river network and 2D mesh network to get correct flood extents. The model has been successfully applied into the Tenpaku basin (Nagoya, Japan), which experienced severe flooding with a maximum flood depth more than 1.5 m on September 11, 2000 when heavy rainfall, 580 mm in 28 hrs (return period >100 yr), occurred over the catchments. Close agreements between the simulated flood depths and observed data ensure that the present integrated modeling approach is able to reproduce the urban flooding situation accurately, which rarely can be obtained through the traditional 1D and 2D modeling approaches.