Results and analysis
Rosetta branch conveyance capacity
evaluation
The current maximum conveyance capacity of the Rosetta Branch is
evaluated by integrating morphological, hydrological, and inundated land
analysis. The morphological analysis shows a trend of deposition along
the Rosetta branch by comparing bed elevation of the years 2003 and
2020. The calculated volume of deposition is about 12.6 million
m3 nearly double the erosion volume of 5.8 million
m3 .The maximum deposition annual rate is 0.22 m/year
also nearly double the maximum erosion annual rate of 0.12 m/year as the
average annual deposition and deposition rates are 3 and 2 cm/year
respectively.
The rating curve of Rosetta Barrage during the years 1964 and 2018 shows
an increase in water elevations due to the deposition trend in the
branch as shown in Figure 6(a). Analysis of water surface elevations
resulting from applying different flow scenarios ranging from 5 to 250
million m3/day in the numerical model shows an
increase in water elevation by an average range of (13-28) cm as shown
in Figure 6(e). Analysis of inundated land area resulting from the same
flow discharge scenarios shows an increase in flooded land by an average
range of (12-200) % as shown in Figure 6(c).
Rosetta branch maximum conveyance capacity experienced a decrease by
25% between the year 2003 and 2020 as the maximum flow discharge that
Rosetta Branch can convey without causing any land on the right or left
bank to be inundated is 30 million m3/day, whereas the
maximum conveyance capacity of the year 2003 was about 40 million
m3/day.
Rehabilitation scenarios
analysis
The three proposed scenarios were evaluated by integrating water surface
elevation, stream velocity, inundated land, and maximum flow conveyance
capacity analyses. Water surface elevation analysis shows that the first
scenario caused a drop in surface water elevation by a range of
(0.07-0.34) m and a total average of 0.15 m. The second scenario caused
a drop in surface water elevation by a range of (0.58-1.28) m and a
total average of 0.89 m. The third scenario caused a drop in surface
water elevation by a range of (0.26-0.59) m and a total average of 0.43
m as shown in Table 2.
The stream velocity analysis shows that the first scenario leads to an
average increase in stream velocity by a percentage of 3.8%. The second
scenario reduced velocity by 1.2%. The third scenario leads to a
reduction in velocity by 8.4%.
The maximum conveyance capacity analysis shows that the first scenario
increased the branch maximum conveyance capacity by a percentage of 33%
making it reach 40 million m3/day before any land
inundation occurs on the left or right banks. The second scenario
increased the branch maximum conveyance capacity by a percentage of 66%
making it reach 50 million m3/day. The third scenario
increased the branch maximum conveyance capacity by a percentage of 33%
making it reach 40 million m3/day.
The inundated land analysis shows that the first scenario caused a
reduction in inundated lands by a range of (7.6-52.2) % with a total
average percentage of 21%. The second scenario caused a reduction in
inundated lands by a range of (16.3-72.9) % with a total average
percentage of 34.3%. The third scenario caused a reduction in inundated
lands by a range of (13.9-70.8) % with a total average percentage of
32.5% as shown in Figure 7 and Table 3.