Channel straightening

increases gradient water drains quickly,
disadvantages - results in more sever flooding down river.
expensive
reduces soil moisture
also slow down rain water going towards sea
disadvantages:
requires large areas of land that will be unavailable for other uses.

deepen+widen channel:
excavation + dredging equipment increase channel size. concrete slabs help reduce friction on river bed improving efficiency of flow. increases discharge flor through channel.
disadvantages:
expensive
creates problems downstream due to increased discharge

artificial levees:
build up river banks using earth + rock increases discharge capacity.

discharge:
expensive
can create problems downstream if breached = massive flooding as river level is much higher than surrounding flood

overflow basins:
designated area of floodplains allowed to flood

dams:
built along tributaries and the main river channel less water released into river during periods of heavy rain. this prevents discharge from rising too much. reservoir levels are increased instead.
Disadvantages:
expensive but can help produce electricity and provide regular water supply.