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.