It has always come to my attention that humans are extremely constructing very close to river banks. Often times, I ask myself questions regarding how we can know that we have constructed very close to the river in a sense that there is high possibility of overflow or flood. To my great dismay, I find problems to find information to address this dilemma. However, I am conscious that for any possible over-flow or flooding event, the extent of flooding van greatly vary from the foot to mouth of the river. So if such scheme exist, I assume that it might be in form of a mathematical formula that can actually bring this into context.
In the USA, riparian zoning laws are used to protect these ecosystems. The buffer width from the stream differs among states and regions. For example, Massachusetts uses about 61m as river protection. Construction or any alteration is prohibited in these zones. In other regions riparian zones focus on water quality protection. For flood assessment, a typical criteria used is 100 year floods to demarcate flood zones for assessing potential disasters. Again the zoning is different in different countries and also depend on land use in these zones.
We have explored aspects of this question for:
(a) UK:
1. https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/j.1477-8696.2001.tb06507.x
2. https://link.springer.com/chapter/10.1007%2F978-1-4020-4200-3_1
3. https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfr3.12305
(b) Norway:
4. https://rgs-ibg.onlinelibrary.wiley.com/doi/abs/10.1111/j.1475-4762.2011.01074.x
5. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1753-318X.2010.01080.x
(c) Czech Republic:
6. https://link.springer.com/chapter/10.1007/978-3-319-42922-9_5
7. https://link.springer.com/article/10.1007%2Fs11027-013-9504-9
8. https://onlinelibrary.wiley.com/doi/full/10.1111/jfr3.12132
As Sania Binte Mahtab mentions above, Canada is another country with many examples, especially London, Ontario and Toronto, Ontario. I have some text in-press on Toronto. Supporting the comment above from Timothy O Randhir about the extensive work across the USA on this topic, I also have a lot of information, not written up, for Boulder, Colorado.
In South Africa the National Water Act sections 121 and 144 requires that flood hazard maps are required for dams or categories of dams with a safety risk and for new developments in urban areas. In urban areas the 1 in 100 year flood extent needs to be estimated before the development can go ahead.. There are no requirements to map flood extents in rural areas. There is a presentation here: https://www.ufs.ac.za/docs/librariesprovider51/annual-conference-in-disaster-risk-reduction-documents/all-documents/m-khoza-134-eng.pdf?sfvrsn=8660cc21_0 on this issue. I worked in South Africa in 1995 and this policy was certainly in place then as I carried out a number of flood studies to define flood extents for new developments.
It is my understanding that in Germany that the official flood maps produced by each Länder (Region) that make the country up have a legal standing in that new developments cannot be constrcuted in these flood zones.
This research project link see: http://www.floodcba.eu/main/?page_id=7359&lang=en gives links to background for the regulatory framework for floods in the UK, Greece, Romania, Portugal, Germany and Spain
I've never heard about a mathematical function allowing description of construction rules in flood-risk areas. Instead, authorities in many countries use categories of flood exposure as a criterion for classification of construction permits.
In France a flood-risk area is an identified space as potentially easily flooded, most of the time because of the presence of a stream among which the water level or the discharge undergoes more or less important variations. If it is not still impossible to build in flood-risk area, it depends on the level of risk. That is why the article L 125-2 of the Environment Law specifies that the citizens have a right for the information about the major risks to which they are exposed.As such, municipalities possess a non-mandatory atlas of the flood-risk areas which can be freely consulted by the population.
In parallel, the law 95-101 of Feb. 2nd, 1995 established Plans of Risk Prevention related to natural and industrial hazards (PPR). Contrary to an atlas , PPR have a statuory value. These plans have for objective to specify the building zones according to the flood risk. Three categories zones are distinguished on PPR:
The red zones are the ones where the risk is the highest and where no new construction is authorized, even by exemption. Blue zones indicate a risk averagely high where the building permit comes along with conditions. Grounds in parking zone are considered as "partially easily flooded". The white zones are considered as without risks and the building permit is submitted to it in the ordinary rules of the land use plan.
You may find more information (I'm afraid only in French) about French regulations in this respect on the Ministry of Environment web site (https://www.ecologique-solidaire.gouv.fr/sites/default/files/Broch_Ame_nagement_A4_web.pdf)
In Zimbabwe Environmental Management Authority (EMA) has a statutory instrument which prohibits interference with land within 30 metres from high flood level (HFL). Ministry of local government issued a circular in 2004 which talks of buffer zones to separate residential development from rivers and other water bodies and this are:
*Around dams 750 metres
*major rivers 500 metres
*Tributaries to major rivers 150 metres
*streams 50 metres
However, in Harare, the capital city, there are houses which are about 20 metres away from the full supply level. I dont know how strong is a circular directive and how long does it lasts. I think a circular is a temporary measure to control an emergency situation pending the formulation of a law or SI. I need to be educated on that one because as a hydrologist in a very volatile catchment i'm facing challenges. ZINWA which is supposed to protect water bodies does not have a specific law or SI to guide its members. For example some hotel owner came to our office asking for our blessing to develop a recreational and leisure fishing resort at one of our dams. We advised him to construct his structures at least 70 m away from the high flood level. He went on to construct gazebos( that is a structure consisting of poles supporting a thatched roof with a cement floor).Now there is an outcry and we were called to explain. Now the problem is for human being its more exciting to be near a body of water and for water management its destructive to have human activity near the banks. The question is how do we approach these conflicting interests. in this particular case what are the negative effect of a structure with 6 poles planted in the ground supporting a thatched roof. Can someone assist because this guy said he has invested more than US$ 20 000 on the project and he gets about 100 customers every weekend day charging $7 per head.
In Germany and the EU is the Directive 2007/60/EC (assessment and management of flood risks) in action.
https://eur-lex.europa.eu/legal-content/en/ALL/?uri=CELEX:32007L0060
This directive became german federal law in the Wasserhaushaltsgesetz (water regime law) chapter 2 section 6 (§§ 72-81). Any construction works are prohibited in areas with flood risk with some exeption cases.
https://www.gesetze-im-internet.de/whg_2009/ (in German)
Flood risk areas are laid down by each german federal state. They were computed from specialized civil engineers in 1D-models (eg manning formula) or 2D-models. Boundaries of the risk areas are in regular cases levees or higher elevated landscape.
https://www.geofachdatenserver.de/de/hochwasserrisikokarte-hq100.html
(example for 100year flood, Federal State Saxony-Anhalt)
If you have further questions, don't hasitate to get in contact.
In the US it's state-to state. In Georgia, there's a 25-ft stream buffer, within which you need a special variance to build. Sometimes local laws are even more restrictive: if you're within the area around Atlanta, it's actually 75 feet. There is a federal standard, usually less restrictive than state rules, called the FEMA floodway. Outside of all of these zones, state, local, and federal, if your building falls within a (generally) 100-year floodplain, you are required to purchase federal flood insurance; you are in effect paying for the FEMA aid you will eventually require WHEN (not if) you get flooded. So there are laws. But they do, generally, still allow people to live in potentially unsafe areas, if they're willing to take on those risks.
Edit: As for formulas, modeling is a little more complicated than just a formula, you need to consider the rainfall, storage potential, and topography of the area. But it can be predicted with some degree of reliability. Modeling using publicly-available programs like HEC-RAS from the U.S. Army Corps of Engineers, can determine flood levels which are then used for regulation.
THE RIVERS AND CANALS ACT 1863 Act 35/1863
Model Building Bye-Laws, 2004
- Badges
- Science topic
- Similar topics
- Geoscience
- Cartography
- Mapping