Tsunami (津波) is phenomenon of raise of the level of water of sea for several meters, that causes destructions in the low–level coastal area if not well protected. Usually tsunamis happen soon (within several minutes) after strong earthquakes. Often, tsunamis are interpreted as surface waves with long wavelength (say, several kilometers), that concentrate in the coastal zone due to the second-order nonlinearity and the group velocity - phase velocity mismatch. Sometimes, the level of water goes down before the significant raise up. There is big article about tsunami at Wikipedia .
Tsunami in Japan
Tsunami often happen in Japan. There exist several kinds of warnings and protection.
Short scale warning
After earthquakes, the trunami warnings appear at the special site http://www.jma.go.jp/jma/indexe.html  in order to alert some tourists who stay at the beach browsing internet. The tsunami warning looks similar to this:
Tsunami Warning/Advisory// Issued at 17:22 JST 07 Dec 2012 ******************Headline****************** Tsunami Warnings (Tsunami) have been issued for the following coastal regions of Japan: MIYAGI PREF. Evacuate immediately to safe place away from the shore in the above coastal regions. Tsunami advisories are currently in effect in other coastal regions of Japan.
The information about earthquake is also provided. Here is example of such a message:
******* Earthquake Information ******** Occurred at 17:18 JST 07 Dec 2012 Region name SANRIKU OKI Latitude 37.8N Longitude 144.2E Depth about 10 km Magnitude 7.3
Long scale warnings
No one ancient rocks with warning 此処より下に家を建てるな  marking the highest historic floodings was reported to be covered at the tsunami. In such a way, one should not say that "unexpectedly high tsunami came".
Any attempt to build-up any constructions below the ancient rocks should be explicitly declared at the construction. Below are two projects of such warnings:
A. This home is build below the ancient marks of tsunami. The builder hopes, that this home is strong enough and the people at the second floor are save even at strong tsunami.
B. This home is build below the ancient marks of tsunami. The builder hopes, that the strong tsunami will not come soon, but if strong earthquake happens, the people should pick up their money and their most important documents and run either up the hill or just out from the sea.
Such warnings do not cost much but they will show certain honesty with respect to the people living in the coastal zone or visiting it. Such warnings are necessary tribute for the ancestors who tried to do that they coluld for several generations ahead.
The walls along the coast, as well as levi along the revers, were supposed to protect buildings from the tsunami. The video records indicate that they do not help. Contrary, they make waterfalls, increasing the destructive ability of tsunami.
Water, jumping from the protecting wall or levi, moves buildings easier than just flood. The wall concentrates the energy of the raising water; the water-fall breaks the nearby buildings. The constructions picked up by the waterfall in vicinity of the protecting wall, move and kick the buildings behind, causing the chain of destruction.
Contrary, the water, just running along the streets, forward and back, does not seem to bring strong destructions. The people saved at the second floor of the strong buildings made many videos confirming this.
On the other hand, very high and very strong protective walls may have sense. According to the Mainichi Shinbun, the Onagawa nuclear plant survived the 2011.03.11 tsunami just due to the engineer Yanosuke Hirai, who insisted to built-up the 14.8-meter-tall shield, instead of the 12 m high shield proposed in the basic project. The tsinami 2011.03.11 is estimated to be 13 meter high. .
The big tsunami of 2011 March 11 is considered as the main reason of the Fukushima disaster: water covered the emergency generators that were supposed to provide the cooling of the shut-down nuclear reactors at the Fukushima nuclear plant. The decay heat was expected to boil and to vaporize the nuclear fuel into the atmosphere, but the suicide workers were able to recover the cooling during March–April, preventing the total contamination of the Honshu island.
One estimates, over Japan, there are hundreds of monuments that indicate the dangerous zones. The hundreds-year letters at the special stones say:"Do not build any homes below this point" (此処より下に家を建てるな) . These stones are reported to protect the citizen who followed the advice of the ancestors and build their homes only above such marks. However, in some cases, the constructors overestimate the ability of the protecting walls to resist tsunami; then some cities are destroyed as the Minami-Sanriku was completely washed-out in 2011 March 11. Some constructions were supposed to be tsunami–resistant, but they fail, killing those who tried to use them as refuges; but many ot those who flee, especially if with cars, survive .
One estimates, between the earthquake that causes a tsunami and the dangerous flow, the people usually have several minutes for escape, especially if they run away from the sea immediately. According to the movies, the main danger at Tsunami is not namely water, but the constructions and cars picked-up by the flow. Some concrete multi-store parkings may resist tsunami, and many videos of tsunamis are filmed from such constructions or natural hills. Perhaps, with building of the metal-concrete homes of several stores, the danger of tsunamis can be significantly decreased.
Danger of ocean tsunami
The main danger of tsunami does not come just from the water, but from the human-made objects: protecting walls that make waterfalls, the constructions that are crashed by these waterfalls (kicking out other constructions), cars that are not parked in a strong garages and therefore are picked up by the flow, the unmanned boats that were not driven into the sea immediately after the earthquake, and so on. Video  shows that boats that leave from the port soon after the earthquake, are safe. The same applies also to the boats reasonably tied at sufficient altitude; other boats are smashed into the buildings, cars, bridges, and destroyed.
The correct preparation to tsunami should be not only building of the "protecting walls", but design of the buildings, car parkings, shops, hotels, homes in such a way, that the water may freely come to the streets and equally free to leave back to the sea, without to flood the operational rooms of a nuclear plant, without to pick up any human, without to pick up any car, without to break any building.
All constructions below the ancient marks must be explicitly marked with visible signs. The building of the protecting walls, that are not designed to resist the flooding, corresponding to the ancient marks, should be prohibited.
Tsunami at rivers
Termin "tsunami" is used for strong floading of rivers, that can carry out the cars and destroy the communications.
2012.07.07, such a "tsunami" is reported at river Bakanka; city Krymsk suffered a lot. The 7meter waves and 10^2 dead were reported ; then the estimate raised to 10^3. The governor of region Aleksandr Tkachev is believed to be guilty for poor organizing of handling of artificial water reservoirs, poor organization of the rescue and misinformation of population . One says, the water raised for several meters after midnight, and do not believe that such a raise could be result of just a rain; before the food, the population were not evacuated, nor even alerted. Officials have not been able to explain the large number of deaths, except by saying that the water swelled in the local Bakanka river and the disaster struck while Krymsk residents were asleep . Many respondents indicate that the tsunami resulted from a sudden release of water from an artificial water reservoir. The Emergencies Ministry says no water drain from reservoirs has been registered. . At the official site of Krymsk administration , the information about raise of level of water did not appear even after the floading (by 2012.07.08) For the explanation of source of that tsunami, Aleksandr Tkachev had suggested the estimate of the precipitation due to the rain in the mounts as 300 liters per square centimeter during a half-day . Inconsistency of such an estimate is an argument in support of the hupothesis that the 7 meter tsunami-like soliton wave had been created at the sudden release of water from the Neberdjaevskoe reservior, converting the flooding to the catastrophe.
2017.05.16, strong tsunami–like flooding in Minvody (минводы), Russia is reported 
- http://www.jma.go.jp/jma/indexe.html Japan Meteorological agency
- http://tamutamu2011.kuronowish.com/kokoyorisitani.htm 此処より下に家を建てるな. (2011) 高き住居は児孫(じそん＝子と孫。子孫)の和楽(わらく＝互いにうちとけて楽しむこと) ／ 想(おも)へ惨禍（さんか＝天災・人災などによる、むごたらしくいたましい災難）の大津浪(おおつなみ) ／此処（ここ）より下に家を建てるな ／ 明治二十九年にも、昭和八年にも津浪は此処まで来て ／ 部落は全滅し、生存者、僅かに前に２人後に４人のみ ／ 幾歳（いくとし）経るとも要心あれ」」 (in Japanese)
- http://www.yomiuri.co.jp/national/news/20110329-OYT1T00888.htm 高き住居は児孫 の和楽 想 へ惨禍の大津浪 おおつなみ. (Yomiuri Shimbun, March 30, 22:07 min, 2011, in Japanese).
- http://www.skyvalleychronicle.com/BREAKING-NEWS/PHOTO-OF-THE-DAY-br-Warning-from-the-ancestors-643751 Warning from the ancestors. April 19, 2011. Here is what this centuries old tablet says: “High dwellings are the peace and harmony of our descendants. Remember the calamity of the great tsunamis. Do not build any homes below this point.”
- http://mdn.mainichi.jp/perspectives/pulse/news/20120319p2a00m0na020000c.html Takao Yamada. Onagawa nuke plant saved from tsunami by one man's strength, determination. 2012.03.19. .. personal strength and tenacity of one Yanosuke Hirai, who passed away in 1986... Hirai was apparently the only person on the entire project to push for the 14.8-meter breakwater, while many of his colleagues said that 12 meters would be sufficient and derided Hirai's proposal as excessive. Hirai's authority and drive, however, eventually prevailed, and Tohoku Electric spent the extra money to build the 14.8-meter-tall shield. Some 40 years later, on March 11, 2011, a 13-meter-high tsunami slammed into the coast at Onagawa.
- http://www.asahi.com/english/TKY201104240105.html Hajime Ueno, Chiaki Ogihara and Takuhei Minamide. Tsunami spared few at elementary school in Ishinomaki. 2011/04/24. ...firefighters went to the elementary school in boats and found that the school building had been reduced to ruins...
- http://www.youtube.com/watch?v=629em0mPpUY Tsunami at Kamaishi port, Iwate Prefecture. Published on Mar 12, 2012. The 311 Tsunami at Kamaishi port in Iwate Prefecture, Japan. Notes: This video is somehow unique, since it shows the actual comings and goings of the tsunami and not just the arrival of the biggest wave. It starts a couple of minutes after the earthquake, probably somewhere around 2:50 and 2:55 pm ..
- http://m.bbc.co.uk/news/world-europe-18751198 Russia flash floods: 134 killed in Krasnodar region. (2012.07.08) .. Regional governor Alexander Tkachev tweeted after flying over the affected area that there was "something unimaginable" going on in Krymsk. .. He said, quoted by the Russian Itar-Tass news agency, that "no-one can remember such floods in our history. There was nothing of the kind for the last 70 years". .. Some users of social media networks in Russia said Krymsk looked like it was hit "by a tsunami". Others accused the authorities of not telling the whole truth about the disaster.
- http://www.rt.com/news/toll-dead-region-floods-633/ Over a hundred killed as tsunami-like flood hits southern Russia (VIDEO, PHOTOS) 07 July, 2012, 13:30, 08 July, 2012, 06:54. More than 140 people have been killed in a devastating flood in Russia’s southern Krasnodar region. It's the worst of its kind in nearly a century, and the death toll continues to rise. .. I don’t know if this is official information or not, but in the city they are saying that they opened the water reservoir in the mountains above the city. That’s where the wave came from. In the city all of a sudden there was 7 meters of water. There was certainly a large storm beforehand, but the water came on so quick that in 15 minutes everything was flooded,” Kovalyovskaya told the Russian News Service.
- http://www.rosbalt.ru/main/2012/07/07/1008362.html Миронов: Противно смотреть, как врет Ткачев. МОСКВА, 7 июля. Лидер партии "Справедливая Россия" Сергей Миронов прокомментировал реакцию региональных властей на сообщения по поводу трагедии в Краснодарском крае, где в результате наводнения погибли более 100 человек. ..
- http://english.alarabiya.net/articles/2012/07/07/225058.html At least 134 killed in southern Russia floods disaster. Saturday, 07 July 2012
- http://www.eurasiareview.com/08072012-southern-russia-hit-by-tsunami-like-flood-over-140-killed/ Southern Russia Hit By Tsunami-Like Flood; Over 140 Killed. July 8, 2012. A Seven-Meter Wave Hit Krymsk In The Middle Of The Night – Witnesses. Anna Kovalyovskaya, whose parents are currently in the flood zone, says that local residents are expressing doubts that a reportedly 7-meter wave could have been caused by the rain storms alone.. “It all happened during the night. People just ran from their homes, because there was a huge wave of water, nobody warned them. Two-story houses were flooded up to the second floor. The water came on very fast. It wasn’t rain.. The Emergencies Ministry says no water drain from reservoirs has been registered. The wave may have been caused by rain waters going down the mountains or rivers breaking the banks, they added..
- http://www.krymsk-region.ru/ Уважаемые дамы и господа! Приветствую Вас от имени жителей муниципального образования Крымский район и от себя лично. Крымский район - одно из старейших поселений Кубани. Гостеприимна, богата, щедра кубанская земля, а Крымский район - частица благодатного и процветающего Краснодарского края. Сердцем района является город Крымск. .. Сегодня инвестиционная привлекательность Крымского района несомненна! .. С уважением. глава муниципального образования. Крымский район. В.В.Крутько (by the state for 2012.07.08)
- http://www.youtube.com/watch?v=ElRjLjIOxmE Крымские басни Ткачёва. Jul 8, 2012 by PycAK4x4. Выступление Ткачёва 8.07.2012 в Крымске около кинотеатра "Русь", и реакция народа на сказки про дождик.
- https://www.youtube.com/watch?v=CCOb_I5A-Ns Аделина Аделя. Минеральные Воды потоп 2017. Published on May 26, 2017
Movies of tsunami
http://www.youtube.com/watch?v=O4_QNqUuUCc fjmfjm8008 on Mar 11, 2011 東北地方太平洋沖地震 千葉県山武市蓮沼の津波の一部始終です。2分20秒に津波が到達します。2011年3月11日大震災の映像です。 The 2011 off the Pacific coast of Tohoku Earthquake TSUNAMI in Chiba prefecture Japan. 11/Mar./2011
http://news.discovery.com/earth/japanese-coast-guard-over-tsunami-waves-video-110321.html Christina Reed. Mon Mar 21, 2011 05:38 PM ET (Boats with engine and crew, that head into the ocean, do well, but those without engine "up" are in problems. The dams and levees seem to just worsen the effect, giving the waves an additional turbulence and acceleration just before the constructions)
http://www.youtube.com/watch?v=BAuWa77vYDU jhn1203 on Jun 17, 2011. New footage of the Japan Tsunami
http://www.youtube.com/watch?v=QralDndMCeQ Dutchmusicfull on Jun 18, 2011
http://www.youtube.com/watch?v=yiENf1f1tIA sean12772 on Mar 20, 2011
http://www.youtube.com/watch?v=4Nxeav0ivhM SEAMANpl on Oct 14, 2010 Ships in rough seas.
http://www.youtube.com/watch?v=6Gw54iSiRH8 dschwartz1114 on Mar 11, 2011. Boat may escape.
http://www.youtube.com/watch?v=tYEAtl8f6r4 TsunamiCollection on Feb 2, 2008 Roof of a car may be a refuge.
http://www.youtube.com/watch?v=GJLT0tm-jWw 3/11/2011 Otsuchi Japan Dramatic Earthquake, Escape and Tsunami footage. (Car escapes from tsunami) bnvn1 on Mar 13, 2011
http://www.youtube.com/watch?v=mj8FuhMpHxE Shocking - Many cars escaping from Tsunami - Japan 3.11. YamachanUS on Mar 26, 2011
Movies of floodings similar to tsunami
http://www.youtube.com/watch?v=caNP0PXZHSk&NR=1 Cezar0051 on Jul 4, 2011
http://www.youtube.com/watch?v=NPwJm8KZND8&NR=1 starkproject on Jul 1, 2010. Из-за ливня в Киеве вода залила ст.м. Харьковская
http://www.youtube.com/watch?v=3KuC2ff-Gmk ValeriiZhelezniakov. Jul 5, 2011. Ливень в Харькове 04.07.2011. Заплыв на дистанцию - улица Героев.
http://www.youtube.com/watch?v=_qFmLY6EXgs&NR=1 yurakl64zx on Jul 4, 2011. Потоп в Харькове 04.07.2011 возле М. Студенческая
http://www.rt.com/news/toll-dead-region-floods-633/ Over a hundred killed as tsunami-like flood hits southern Russia (VIDEO, PHOTOS) Published: 07 July, 2012, 13:30 Edited: 08 July, 2012, 06:54
http://www.iwate-np.co.jp/cgi-bin/topnews.cgi?20110403_11 ここより下に家を建てるな 宮古、集落守った石碑 (2011/04/03, In Japanee).
http://tamutamu2011.kuronowish.com/kokoyorisitani.htm 岩手県宮古市の姉吉（あねよし）に建つ「大津浪記念碑」 １８９６（明治２９）年６月１５日午後７時３２分３０秒に発生した地震（震源は岩手県上閉伊郡釜石町〈現・釜石市〉の東方沖２００km。... １９３３（昭和８）年３月３日午前２時３０分に、発生した昭和三陸地震（震源は岩手県上閉伊郡釜石町〈現・釜石市〉の東方沖約２００Ｋｍ。 (In Japanese)
http://www.heraldsun.com.au/news/breaking-news/japanese-fishing-boat-found-floating-off-canada-more-than-a-year-after-tsunami/story-e6frf7k6-1226309024929 Japanese fishing boat found floating off Canada more than a year after tsunami. March 24, 2012 5:47PM. The 46-metre vessel was about 222km off British Columbia's Queen Charlotte Islands, KING 5 News reported. Japanese officials said the boat was lost from Hokkaido after the March 11, 2011, earthquake and tsunami, according to Canada's CHAN-DT. Its owner is also listed as missing, but is not believed to have been on board. The boat - the first piece of large tsunami debris to reach North America - would have reached the coast in about 50 days, but will be removed before then.
http://japandailypress.com/mayor-of-tsunami-devastated-town-in-fukushima-facing-criminal-negligence-2810379 Adam Westlake. Mayor of tsunami-devastated town in Fukushima facing criminal negligence. August 28, 2012. While Jin Sato, Mayor of the town Minamisanriku, in Fukushima Prefecture, was originally praised as a hero for his dedication to sending tsunami warning messages to the public last year, he is now looking at charges of professional negligence for the deaths of 41 public officials.
2015.06.24. https://www.youtube.com/watch?v=PjtoOMIk-D4 Шокирующее видео цунами в Японии. Новые кадры. meteor777hits. Published on Jun 24, 2015. Шокирующее видео цунами в Японии. Кто не спрятался я не виноват