I am a hydrologist, not an engineer.  My answer is Probably not what you are seeking, but identify floodplains and avoiding them with structures, or retrofitting structures to withstand flooding.  Need better and long term stream gaugung and flood records, and applying those data to the situation, along with rainfall records.  Better understanding of hydrologic modifications and their effect on flooding risk.  Dam maintenance, stormwater design to detain flow to reduce flood peaks.  Understanding land use change often leads to increased flooding issues.  Stream channelization and gullying, excess sedimentation with channel filling contribute to flooding on some portions of a watershed.  Certainly there are things that can be done to protect specific areas, they involve analysis and design, a recognition of the risk, some labor intensive and costly actions, and expectation that long term design, even at its best, will include potential for both success and failure.  Many technical skills may apply to help develop integrated flood management, design, maintenance and emergency forecast and response.  If a 20 cm rainfall is forecast in a week, things should be happening, such as dams lowered, check any levees, culverts for blockage, coordinated well managed effort.  Individuals tend to be unaware or last minute response, control limited ability to do much on their own, so community or government assistance is probably needed, so flood management and action planning including emergency funding of resources available immediately when responible official decides action is needed.  Lives can be saved with improved education and actions such as active road closures when flooded.

I am a hydrologist, not an engineer.  My answer is Probably not what you are seeking, but identify floodplains and avoiding them with structures, or retrofitting structures to withstand flooding.  Need better and long term stream gaugung and flood records, and applying those data to the situation, along with rainfall records.  Better understanding of hydrologic modifications and their effect on flooding risk.  Dam maintenance, stormwater design to detain flow to reduce flood peaks.  Understanding land use change often leads to increased flooding issues.  Stream channelization and gullying, excess sedimentation with channel filling contribute to flooding on some portions of a watershed.  Certainly there are things that can be done to protect specific areas, they involve analysis and design, a recognition of the risk, some labor intensive and costly actions, and expectation that long term design, even at its best, will include potential for both success and failure.  Many technical skills may apply to help develop integrated flood management, design, maintenance and emergency forecast and response.  If a 20 cm rainfall is forecast in a week, things should be happening, such as dams lowered, check any levees, culverts for blockage, coordinated well managed effort.  Individuals tend to be unaware or last minute response, control limited ability to do much on their own, so community or government assistance is probably needed, so flood management and action planning including emergency funding of resources available immediately when responible official decides action is needed.  Lives can be saved with improved education and actions such as active road closures when flooded.

Dear Osama,

probably the answer is: "It depends". It depends on the area (geological characteristics, topography), on the hydrologic regime (as William said) and so on...

As Kleomenis mentions, it depends to a large extent on the geographic, hydrological and hydraulic characteristics as well as on other factors such as population density and economic value in protected areas what kind of protection strategy is most benefitial (economically, socially, ecologically etc.). Generally, a mixture of long-term and short-term measures should be taken and prepared. Long-term measures include management of upstream areas (e.g. restoration of retention function of these areas, reforestation), increase of river capacity (e.g. deepening and widening of main channel and/ or flood plains), dike enforcement and spatial planning and awareness raising in downstream areas to reduce flood risks. Short-term measures include improvement of flood early warning and emergency evacuation plans and exercises.

In addition to those written above you can check International Flood Initiative ( http://www.ifi-home.info/IFI-Concept.html ). Here you can find the principles of integrated flood management. One of the ideas is to leave the idea of fighting with floods for a better one - living with floods. Good luck.

I agree with above comments. It is crucial to understand flood is a nature force that cannot by fully controlled by humans. The old cultures (ancient Egyptians, Mesopotamia culture...) were connected to floods - particularly with agriculture. Their strategy was to use fertile flood sediments for farming. So, their fields were placed at floodplains, but their settlements were situated apart of reach of water. This is one of recent problems - present urban management miss "flood memory". Second thing is wrong landscape management. Across the literature you can find articles accentuate favourable effect of forests on floods/water retention (detention, accumulation, infiltration...). We have studied one catchment with 92 percent (!) of forest coverage that was frequently affected by floods. Forests are interlaced with dense forest roads (density 62 m/ha) and 40% of forests were younger than 40 years. Another problem is connected to urban sprawl and soil sealing. There are studies revealing that 46 percent of urban coverage is totally impervious. Subsequent surface runoff is 64 times (!) higher compared to runoff from natural catchment. The average runoff from city of 78 thousand inhabitants varies from 5.0 – 6.2 million cubic meters. Can you imagine what could happen with a stormwater runoff during a torrential rain? My answer is suitable and sensitive management. Of course, when I return to prelude, flood is a nature hazard. Sometimes you just have to fall back.

if someone´s interested:

http://www.agriculturejournals.cz/publicFiles/173201.pdf

https://www.researchgate.net/publication/259163858_Hydric_potential_of_selected_river_basins_in_Slovakia?ev=prf_pub

Article Hydric potential of selected river basins in Slovakia

Agreeing with what's said above: it depends and living with floods is a more sustainable option in the long term than just fighting them. 

There's an important role for floodplains, and measures will be a mix of the whole risk management cycle: preventing flood damage by keeping flood plains free of infrastructure, protection, by infrastructure where no other option is possible, preparedness with forecasting and early warning systems, and plans in place (and trained) fr the response phase and recovery if it happens. 

besides scientific journal papers, and national studies, some overviews can be found in:

http://www.eea.europa.eu/publications/water-resources-and-vulnerability

http://www.eea.europa.eu/publications/flood-risks-and-environmental-vulnerability

https://circabc.europa.eu/sd/a/acbcd98a-9540-480e-a876-420b7de64eba/Floods%20Reporting%20guidance%20-%20final_with%20revised%20paragraph%204.2.3.pdf (mainly for the annexes)

First we need to understand the basin hydrology. The trends and the pattren of the rainfall. Then the developments in the region and the changes in the landuse pattren.

Dear Osama,

 I am merely a student in the field of Geomorphology. I want to share my experience with you about your question.River intention is same through out all climatic and geo-hydrological environment -to perform max. work expending min. energy. Mainly she want to maintain the negative feedback system.You know, river transport capacity depend on HR. When the value of HR decrease due to sedimentation, the river want to increase HR. And the river creates a flash of water into its channel which erodes the river channel itself and subsequently increase the HR. But if the channel is too shallow to contain this flash water, it overflows and the result is flood. If you take any anti flood activities ignoring this internal management , the attempt will be harmful to the river. At first you should study the river, more appropriate  the energy level of the river weather the river is able to maintain this mechanism at all.  If the river is able to maintain that, should not disturb the river but occasional increasing The HR. If you understand , the river is inefficient , the river is almost dead and your any attempt will not fruitful but it accelerates its agony . Lastly I want to say , all depend on what are your observations  about the river. Thanking you, With regards, Madhab Mondal, India.     

Dear All,

We must understand total freedom from flood is neither possible nor desirable. It need not  be viewed as disaster but as hydrological extreme rendering many ecological services. Since I live in the GB delta I look it as sediment dispersal mechanism; it flushes the sediment to deeper estuary, recharges groundwater and helps pollution abatement. The attempt to control flood by building embankment ultimately proved futile in Bengal. Even the multipurpose river valley project did not work to the level of expectation. We can manage urban waterlogging but not the flood that submerge rural Bengal. The proper flood management can reduce the distress of the afflicted community.

Kalyan Rudra, Kolkata.