Complex sentence: Many projects developed by engineers and surveyors between 1741 to 1787 plan to divert waters of the river south of the city as an insurmountable obstacle, but lack of resources, these projects yet approved by the board of Bridges and Roads, are permanently abandoned in 1790.
Split into simpler sentences: Many projects developed by engineers and surveyors between 1741 and 1787 were plans to divert waters of the river south of the city. But due to lack of resources, these projects remained for the approval by the board of Bridges and Roads; they were permanently abandoned in 1790.