Banjir: Perbezaan antara semakan
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Baris 43:
* '''Bekalan air'''- Pencemaran bekalan air. Air bersih akan sukar dicari.<br />
* '''Tanaman dan bekalan makanan'''- Kekurangan bekalan makanan akibat kemusnahan tanaman yang dimusnahkan air banjir.<ref>[http://www.southasianfloods.org southasianfloods.org]</ref>
===Kesan Utama===
Kesan utama banjir termasuk kehilangan nyawa, kerosakan bangunan dan struktur lain, termasuk jambatan, sistem pembetungan, jalan raya dan terusan.
Banjir juga sering merosakkan penyambungan eletrik dan kadang-kadang penjanaan kuasa, yang kemudiannya mempunyai kesan hiliran akibat kehilangan kuasa eletrik. Ini termasuk kehilangan rawatan air minum dan bekalan air, yang mungkin mengakibatkan ketiadaan air minuman atau pencemaran air yang teruk. Ia juga boleh menyebabkan ketiadaan kemudahan pelupusan kumbahan. Kekurangan air bersih digabungkan dengan kumbahan manusia di dalam air banjir menimbulkan risiko penyakit air yang boleh merangkumi [[deman kepialu]], giardia, [[cryptosporidium]], [[kolera]] dan banyak penyakit lain bergantung kepada lokasi banjir.
Kerosakan kepada jalan dan infrastruktur pengangkutan mungkin menysukarkan untuk menggerakkan bantuan kepada mereka yang terjejas atau penyediakan rawatan kecemasan.
Air banjir biasanya membanjiri tanah ladang, menjadikan tanah itu tidak boleh dikerjakan dan menghalang tanaman daripada ditanam atau dituai, yang boleh mengakibatkan kekurangan makanan baik untuk manusia dan haiwan ladang. Tanaman seluruh negara boleh hilang dalam keadaan banjir yang melampau. Sesetengah spesies pokok tidak boleh bertahan banjir berpanjangan pada sistem akar mereka.<ref>Stephen Bratkovich, Lisa Burban, et al., [http://www.na.fs.fed.us/spfo/pubs/n_resource/flood/cover.htm "Flooding and its Effects on Trees"], [[USDA Forest Service]], Northeastern Area State and Private Forestry, St. Paul, MN, September 1993</ref>
===Kesan jangka kedua dan jangka panjang==
Kesukaran ekonomi akibat kemerosotan sementara pada pelancongan, kos membina semula, atau kekurangan makanan yang membawa kepada kenaikan harga merupakan kesan selepas berlakunya banjir yang teruk. Kesan kepada mereka yang terjejas boleh menyebabkan kerosakan psikologi kepada mereka yang terjejas, khususnya di mana berlaku kematian, kecederaan serius dan kehilangan harta benda.
Banjir di bandar boleh membawa kepada rumah-rumah basah kronik, yang dikaitkan dengan peningkatan pada masalah pernafasan dan penyakit lain.<ref>Indoor Air Quality (IAQ) Scientific Findings Resource Bank (IAQ-SFRB), [http://www.iaqscience.lbl.gov/dampness-risks-house.html "Health Risks or Dampness or Mold in Houses"] {{webarchive|url=https://web.archive.org/web/20131004213929/http://www.iaqscience.lbl.gov/dampness-risks-house.html |date=2013-10-04 }}</ref> Banjir di bandar juga mempunyai implikasi ekonomi yang ketara pada kejiranan yang terjejas. Di Amerika Syarikat, para ahli industri menganggarkan bahawa ruang bawah tanah yang basah dapat menurunkan nilai harta sebanyak 10-25 peratus dan dipetik di antara alasan utama untuk tidak membeli rumah tersebut.<ref>Center for Neighborhood Technology, Chicago IL [http://www.cnt.org/resources/the-prevalence-and-cost-of-urban-flooding/ "The Prevalence and Cost of Urban Flooding"], May 2013</ref> Menurut Agensi Pengurusan Kecemasan Persekutuan Amerika Syarikat (FEMA), hampir 40 peratus perniagaan kecil tidak pernah membuka semula perniagaan mereka berikutan bencana banjir..<ref>[http://www.fema.gov/protecting-yourbusinesses "Protecting Your Businesses"]{{dead link|date=June 2017 |bot=InternetArchiveBot |fix-attempted=yes }}, last updated March 2013</ref> Di Amerika Syarikat, insurans boleh didapati bagi kerosakan banjir kepada kedua-dua rumah dan perniagaan.<ref name=NFIP>{{cite web|title=National Flood Insurance Program|url=https://www.floodsmart.gov/floodsmart/ |website=FloodSmart.gov|accessdate=2015-07-06}}</ref>
===Faedah===
Banjir (terutamanya banjir yang lebih kerap atau lebih kecil) juga boleh membawa banyak faedah, seperti pengisian air tanah, menjadikan tanah lebih subur dan meningkatkan nutrien di sesetengah tanah. Air banjir menyediakan sumber air yang sangat diperlukan di kawasan - kawasan yang gersang dan separa gersang di mana hujan mingkit tersebar secara tidak rata sepanjang tahun dan membunuh perosak di tanah pertanian. Banjir air tawar terutamanya memainkan peranan penting dalam mengekalkan ekosistem di koridor sungai dan merupakan faktor utama dalam mengekalkan biodiversiti dataran banjir.<ref>WMO/GWP Associated Programme on Flood Management, [http://www.apfm.info/publications/policy/ifm_env_aspects/Environmental_Aspects_of_IFM_En.pdf "Environmental Aspects of Integrated Flood Management"], 2007</ref> Banjir boleh menyebarkan nutrien ke tasik dan sungai, yang boleh membawa peningkatan biomas dan perikanan yang bertambah baik selama beberapa tahun.
Bagi sesetengah spesies ikan, sebuah dataran banjir yang dibanjiri boleh membentuk lokasi yang sangat sesuai untuk penghijrahan dengan kurang pemangsa dan tahap nutrien atau makanan yang meningkat..<ref>[http://kops.ub.uni-konstanz.de/volltexte/2009/7515/pdf/2008_Wantzen_etal_An_extension_of_the_floodpulse.pdf Extension of the Flood Pulse Concept], Retrieved on 2012-06-12</ref> Ikan boleh menggunakan banjir untuk sampai ke habitat baru. Populasi burung juga dapat meraih keuntungan dari peningkatan pengeluaran makanan yang disebabkan oleh banjir.<ref>[http://africa.ipsterraviva.net/2010/10/15/birdlife-soars-above-botswanas-floodplains Birdlife soars above Botswana's floodplains] {{webarchive|url=https://web.archive.org/web/20110209093150/http://africa.ipsterraviva.net/2010/10/15/birdlife-soars-above-botswanas-floodplains/ |date=2011-02-09 }} (2010-10-15), Retrieved on 2012-06-12</ref>
Banjir berkala adalah penting untuk kesejahteraan masyarakat purba di sepanjang Sungai Tigris-Euphrates, Sungai Nil, Sungai Indus, Sungai Gangga, dan Sungai Kuning antara lain. Daya maju kuasa hidro, sumber tenaga boleh diperbaharui, juga lebih tinggi di kawasan rawan banjir.
==Flood safety planning==
At the most basic level, the best defense against floods is to seek higher ground for high-value uses while balancing the foreseeable risks with the benefits of occupying flood hazard zones.<ref name="Eychaner">Eychaner, J.H. (2015) ''Lessons from a 500-year record of flood elevations'', [http://www.floods.org/ace-files/documentlibrary/publications/asfpmpubs-techrep7_2015.pdf Association of State Floodplain Managers, Technical Report 7], Accessed 2015-06-27</ref>{{rp|22–23}} Critical community-safety facilities, such as hospitals, emergency-operations centers, and police, fire, and rescue services, should be built in areas least at risk of flooding. Structures, such as bridges, that must unavoidably be in flood hazard areas should be designed to withstand flooding. Areas most at risk for flooding could be put to valuable uses that could be abandoned temporarily as people retreat to safer areas when a flood is imminent.
Planning for flood safety involves many aspects of analysis and engineering, including:
* observation of previous and present flood heights and inundated areas,
* statistical, [[hydrologic]], and hydraulic model analyses,
* mapping inundated areas and flood heights for future flood scenarios,
* long-term [[land use planning]] and regulation,
* [[engineering design]] and construction of structures to control or withstand flooding,
* intermediate-term monitoring, [[Flood forecasting|forecasting]], and emergency-response planning, and
* short-term monitoring, [[Flood warning|warning]], and response operations.
Each topic presents distinct yet related questions with varying scope and scale in time, space, and the people involved. Attempts to understand and manage the mechanisms at work in floodplains have been made for at least six millennia.<ref>Dyhouse, G., "Flood modelling Using HEC-RAS (First Edition)", Haestad Press, Waterbury (USA) 2003</ref>{{page needed|date=July 2015}}
In the United States, the Association of State Floodplain Managers works to promote education, policies, and activities that mitigate current and future losses, costs, and human suffering caused by flooding and to protect the natural and beneficial functions of floodplains – all without causing adverse impacts.<ref>{{cite web|title=Association of State Floodplain Managers|url=http://floods.org/ |accessdate=2015-07-13}}</ref> A portfolio of [[best practice]] examples for [[disaster mitigation]] in the United States is available from the Federal Emergency Management Agency.<ref>{{cite web|title=Best Practices Portfolio|url=http://www.fema.gov/mitigation-best-practices-portfolio |publisher=Federal Emergency Management Agency|accessdate=2015-07-06}}</ref>
===Control===
:{{Main article|Flood control}}
In many countries around the world, waterways prone to floods are often carefully managed. Defenses such as [[detention basin]]s, [[levee]]s,<ref>{{Cite book|title=Levees and Other Raised Ground|author=Henry Petroski|publisher=American Scientist|year=2006|volume=94|issue=1|pages=7–11}}</ref> [[bunding|bunds]], [[reservoir (water)|reservoirs]], and [[weir]]s are used to prevent waterways from overflowing their banks. When these defenses fail, emergency measures such as [[sandbag]]s or portable inflatable tubes are often used to try to stem flooding. Coastal flooding has been addressed in portions of Europe and the Americas with [[Coastal management|coastal defenses]], such as [[sea wall]]s, [[beach nourishment]], and [[barrier island]]s.
In the [[riparian zone]] near rivers and streams, [[erosion control]] measures can be taken to try to slow down or reverse the natural forces that cause many waterways to meander over long periods of time. Flood controls, such as dams, can be built and maintained over time to try to reduce the occurrence and severity of floods as well. In the United States, the [[U.S. Army Corps of Engineers]] maintains a network of such flood control dams.
In areas prone to urban flooding, one solution is the repair and expansion of man-made sewer systems and stormwater infrastructure. Another strategy is to reduce impervious surfaces in streets, parking lots and buildings through natural drainage channels, [[porous paving]], and [[wetlands]] (collectively known as [[green infrastructure]] or [[sustainable urban drainage systems]] (SUDS)). Areas identified as flood-prone can be converted into parks and playgrounds that can tolerate occasional flooding. Ordinances can be adopted to require developers to retain stormwater on site and require buildings to be elevated, protected by [[floodwall]]s and [[levees]], or designed to withstand temporary inundation. Property owners can also invest in solutions themselves, such as re-landscaping their property to take the flow of water away from their building and installing [[rain barrels]], [[sump pump]]s, and [[check valve]]s.
==Analysis of flood information==
A series of annual maximum flow rates in a stream reach can be analyzed [[extreme value analysis|statistically]] to estimate the 100-year flood and floods of other [[return period|recurrence intervals]] there. Similar estimates from many sites in a hydrologically similar region can be related to measurable characteristics of each drainage basin to allow [[regression analysis|indirect estimation]] of flood recurrence intervals for stream reaches without sufficient data for direct analysis.
Physical process models of channel reaches are generally well understood and will calculate the depth and area of inundation for given channel conditions and a specified flow rate, such as for use in floodplain mapping and [[flood insurance]]. Conversely, given the observed inundation area of a recent flood and the channel conditions, a model can calculate the flow rate. Applied to various potential channel configurations and flow rates, a reach model can contribute to selecting an optimum design for a modified channel. Various reach models are available as of 2015, either [[One-dimensional space|1D]] models (flood levels measured in the [[stream channel|channel]]) or [[Two-dimensional space|2D]] models (variable flood depths measured across the extent of a floodplain). [[HEC-RAS]],<ref>United States Army Corps of Engineers, Davis, CA, [http://www.hec.usace.army.mil Hydrologic Engineering Center]</ref> the Hydraulic Engineering Center model, is among the most popular [[software]], if only because it is available free of charge. Other models such as TUFLOW<ref>BMT WBM Pty Ltd., Brisbane, Queensland, [http://www.tuflow.com "TUFLOW Flood and Tide Simulation Software"] {{webarchive|url=https://web.archive.org/web/20080627014611/http://www.tuflow.com/ |date=2008-06-27 }}</ref> combine 1D and 2D components to derive flood depths across both river channels and the entire floodplain.
[[computer simulation|Physical process models]] of complete drainage basins are even more complex. Although many processes are well understood at a point or for a small area, others are poorly understood at all scales, and process interactions under normal or extreme climatic conditions may be unknown. Basin models typically combine land-surface process components (to estimate how much rainfall or snowmelt reaches a channel) with a series of reach models. For example, a basin model can calculate the runoff [[hydrograph]] that might result from a 100-year storm, although the recurrence interval of a storm is rarely equal to that of the associated flood. Basin models are commonly used in flood forecasting and warning, as well as in analysis of the effects of land use change and [[climate change]].
===Flood forecasting===
{{Main article|Flood forecasting|flood warning|}}
Anticipating floods before they occur allows for precautions to be taken and people to be warned <ref>{{cite web|url=http://www.environment-agency.gov.uk/homeandleisure/floods/58417.aspx |title=Flood Warnings|publisher=Environment Agency|date=2013-04-30|accessdate=2013-06-17}}</ref> so that they can be prepared in advance for flooding conditions. For example, farmers can remove animals from low-lying areas and utility services can put in place emergency provisions to re-route services if needed. Emergency services can also make provisions to have enough resources available ahead of time to respond to emergencies as they occur. People can evacuate areas to be flooded.
In order to make the most accurate flood forecasts for [[waterway]]s, it is best to have a long time-series of historical data that relates [[stream flow]]s to measured past rainfall events.<ref>{{cite web|url=http://www.bom.gov.au/australia/flood |title=Australia rainfall and river conditions|publisher=Bom.gov.au|date= |accessdate=2013-06-17}}</ref> Coupling this historical information with [[Real-time data|real-time knowledge]] about volumetric capacity in catchment areas, such as spare capacity in reservoirs, ground-water levels, and the degree of [[Phreatic zone|saturation]] of area [[aquifer]]s is also needed in order to make the most acrate flood forecasts.
[[Weather radar|Radar]] estimates of rainfall and general [[weather forecasting]] techniques are also important components of good flood forecasting. In areas where good quality data is available, the intensity and height of a flood can be predicted with fairly good accuracy and plenty of lead time. The output of a flood forecast is typically a maximum expected water level and the likely time of its arrival at key locations along a waterway,<ref name="Advanced Hydrologic Prediction System">{{cite web|url=http://water.weather.gov/ahps |title=Advanced Hydrologic Prediction System|accessdate=4 February 2013}}</ref> and it also may allow for the computation of the likely statistical return period of a flood. In many developed countries, urban areas at risk of flooding are protected against a 100-year flood – that is a flood that has a probability of around 63% of occurring in any 100-year period of time.
According to the U.S. [[National Weather Service]] (NWS) Northeast River Forecast Center (RFC) in [[Taunton, Massachusetts]], a rule of thumb for flood forecasting in urban areas is that it takes at least {{convert|1|in|mm}} of rainfall in around an hour's time in order to start significant [[ponding]] of water on [[Impervious surface|impermeable surfaces]]. Many NWS RFCs routinely issue Flash Flood Guidance and Headwater Guidance, which indicate the general amount of rainfall that would need to fall in a short period of time in order to cause flash flooding or flooding on larger [[water basin]]s.<ref name="Flash Flood Guidance">{{cite web|url=http://www.srh.noaa.gov/rfcshare/ffg.php |title=FFG|accessdate=29 January 2013}}</ref>
In the United States, an integrated approach to real-time hydrologic computer modelling utilizes observed data from the [[U.S. Geological Survey]] (USGS),<ref name="USGS WaterWatch">{{cite web|url=http://waterwatch.usgs.gov/index.php?id=ww_current |title=WaterWatch|date=4 February 2013|accessdate=4 February 2013}}</ref> various [[Weather spotting|cooperative observing networks]],<ref name="Community Collaborative Rain, Hail and Snow Network">{{cite web|url=http://www.cocorahs.org |title=Community Collaborative Rain, Hail and Snow Network|accessdate=4 February 2013}}</ref> various [[Automated airport weather station|automated weather sensors]], the [[NOAA]] National Operational Hydrologic Remote Sensing Center (NOHRSC),<ref name="National Operational Hydrologic Remote Sensing Center">{{cite web|url=http://www.nohrsc.noaa.gov |title=NOHRSC|date=2 May 2012|accessdate=4 February 2013}}</ref> various [[hydroelectric]] companies, etc. combined with [[quantitative precipitation forecast]]s (QPF) of expected rainfall and/or snow melt to generate daily or as-needed hydrologic forecasts.<ref name="Advanced Hydrologic Prediction System"/> The NWS also cooperates with [[Environment Canada]] on hydrologic forecasts that affect both the USA and Canada, like in the area of the [[Saint Lawrence Seaway]].
The Global Flood Monitoring System, "GFMS," a computer tool which maps flood conditions worldwide, is available [http://flood.umd.edu/ online]. Users anywhere in the world can use GFMS to determine when floods may occur in their area. GFMS uses precipitation data from [[NASA]]'s Earth observing satellites and the [[Global Precipitation Measurement satellite]], "GPM." Rainfall data from GPM is combined with a land surface model that incorporates vegetation cover, soil type, and terrain to determine how much water is soaking into the ground, and how much water is flowing into [[streamflow]].
Users can view statistics for rainfall, streamflow, water depth, and flooding every 3 hours, at each 12 [[kilometer]] gridpoint on a global map. Forecasts for these parameters are 5 days into the future. Users can zoom in to see inundation maps (areas estimated to be covered with water) in 1 kilometer resolution.<ref>{{Cite web|title=Predicting Floods|url=https://science.nasa.gov/science-news/science-at-nasa/2015/22jul_floods/ |website=science.nasa.gov|accessdate=2015-07-22}}</ref><ref>{{cite av media|url=https://www.youtube.com/watch?v=dfcr-4XmxNY&authuser=0 |title=ScienceCasts: Predicting Floods|date=21 July 2015|publisher=YouTube|accessdate=13 January 2016|via=YouTube}}</ref>
== Kejadian-kejadian banjir yang terkenal کجادين٢ بنجير يڠ ترکنل ==
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