Straightening Operations

Straightening Operations 

hydraulic-engineering work on the slopes of river valleys and in riverbeds to control the action of river currents, ensure normal conditions for navigation and log floating, and protect riverbanks and structures from local erosion or drift deposition. Straightening operations help to equalize the erosive force of currents and the resistance of channels to erosion and to balance the amount of sediment brought into a stream and the stream’s ability to transport it further.

Straightening operations on rivers include strengthening the slopes of river valleys to decrease the total quantity of sediment entering the riverbeds and to reduce the intensity of soil erosion; closing off channels and straightening bends in riverbeds, which increases longitudinal gradients and the average current speed, giving the riverbed a more stable form; increasing the depth of channels with suction and bucket dredges; and the construction of control and shore-reinforcement works.

Very effective methods proposed by the Soviet scientists M. V. Potapov and A. I. Losievskii are being used successfully to control channel erosion. The Potapov method pre-vents the destruction of banks, erosion of the river bottom near installations, and the deposition of drift in water intakes and irrigation canals by controlling the hydraulic structure of the current—that is, by creating artificial cross circulation, which changes the natural direction and the characteristics of motion of sediment. Cross circulation of the current is provided by a system of directing panels, which cause a helical water current in the required direction. The Losievskii method is used to combat sedimentation in navigable rivers; here the circulation of the flow is created by baffles set into the bottom at angles of 20°-50° to the current. This deflects surface currents downward and deflects drift-saturated bottom currents toward shore.

Straightening operations and related construction depend mostly on local building materials for construction of gabions, fascines, protective wattles and fences, brushwork mattresses, and rock and gravel revetments.

REFERENCES

Grishin, M. M. Gidrotekhnicheskie sooruzheniia. Moscow, 1968.
Degtiarev, V. V. Vypravlenie rek, 2nd ed. Moscow, 1968.

N. N. PASHKOV