CIV E 530 - OPEN-CHANNEL HYDRAULICS
SPRING 2007
HOMEWORK No. 7

The 10-km reach of the Paraguay river downstream of Caceres, Brazil, has the following hydraulic and cross-sectional characteristics:

Discharge Q = 500 m3/sec; bottom width b = 300 m; side slope z (inbank) = 1, equilibrium slope So = 0.00005; Manning n (inbank) = 0.030; Manning n (outbank) = 0.045; bank-full depth yb = 5 m; left flood-plain width = 1000 m; right flood-plain width = 1000 m; side slope z (at the end of flood plain) = 1; flood-plain depth (to characterize cross section) = 5 m.

The upstream invert elevation (section 0+000) is 100 m.

  1. Baseline. Calculate the baseline water-surface profile using BACKWATER in http://onlinecomp.sdsu.edu. Use 11 equally-spaced cross sections. To specify downstream stage, first calculate normal depth using CHANNEL in http://onlinecomp.sdsu.edu. Use three significant digits for the normal depth. Print a table showing the water-surface elevations at all 11 (eleven) cross sections.

  2. Hydraulic effect of local dredging. Calculate the maximum drop in water surface elevation and its location along the channel, when the bottom of the channel is dredged 3 m between sections 4+000 and 8+000, inclusive. Assume same side slope (inbank) for dredging cut. Print a table showing the water-surface elevations at all 11 (eleven) cross sections. Report the maximum stage difference between Case 1 and Case 2 and its location along the channel. What can you conclude from this exercise?

  3. Hydraulic effect of general dredging. Calculate the maximum drop in water surface elevation when the bottom of the channel is dredged 3 m throughout its length. Assume same side slope (inbank) for dredging cut. To specify downstream stage, first calculate normal depth using CHANNEL in http://onlinecomp.sdsu.edu. Use three significant digits for the normal depth. Print a table showing the water-surface elevations at all 11 (eleven) cross sections. Report the (equal) stage difference along the channel between Case 1 and Case 3. What can you conclude from this exercise?

  4. Effect of dredging on hydrology. With the 3-m dredging in place throughout the channel, use BACKWATER to calculate, by trial and error, the discharge that will restore the water-surface profile (stage and water-surface slope) to its baseline position (Case 1). Use four significant digits for the restoring discharge. Report the value of discharge that will restore the dredged channel to its baseline stage position. What can you conclude from this exercise?