{"id":450,"date":"2024-07-02T09:09:27","date_gmt":"2024-07-02T09:09:27","guid":{"rendered":"https:\/\/study.madeeasy.in\/?p=450"},"modified":"2025-09-08T12:17:53","modified_gmt":"2025-09-08T06:47:53","slug":"instantaneous-unit-hydrograph","status":"publish","type":"post","link":"https:\/\/www.madeeasy.in\/study\/ce\/engineering-hydrology\/instantaneous-unit-hydrograph","title":{"rendered":"Instantaneous Unit Hydrograph"},"content":{"rendered":"\r\n<p style=\"text-align: justify;\">A number of unit hydrographs can be drawn for a catchment corresponding to different durations. The shape of unit hydrographs depends on duration of <em>D<\/em>. Figure below shows a typical variation of shape of unit hydrographs for different values of <em>D<\/em>. As the value of <em>D <\/em>will decrease, intensity of rainfall excess being equal to 1D increases and unit hydrograph can also be drawn for a duration of rainfall approximately equal to zero. Thus, limiting case of a unit hydrograph of zero duration is known as instantaneous unit hydrograph (IUH). Thus, of IUH is a fictious unit hydrograph which represents surface runoff from catchment due to an instantaneous precipitation of rainfall excess volume of 1 cm. Let, ordinate of IUH is denoted by <em>u<\/em>(<em>t <\/em>). Then, some of the properties of IUH can be listed as follows:<\/p>\r\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-274 aligncenter\" src=\"http:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/unit-hydrograph.jpg\" alt=\"Unit Hydrograph\" width=\"512\" height=\"365\" \/><\/p>\r\n<p style=\"text-align: justify;\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-276 size-full aligncenter\" src=\"http:\/\/study.madeeasy.in\/wp-content\/uploads\/2024\/07\/derivation-of-d-hour-1.jpg\" alt=\"Derivation of D-hour\" width=\"711\" height=\"464\" \/><\/p>\r\n<p style=\"text-align: justify;\"><strong>NOTE:<\/strong><\/p>\r\n<ul style=\"text-align: justify;\">\r\n<li>It occurs when <em>D-&gt;<\/em>0 is used for IUH, it is also known as T<em>ime-area histogram method.<\/em><\/li>\r\n<li>It is assumed that the rainfall excess first undergoes pure translation and then attenuation.<\/li>\r\n<\/ul>\r\n<h4 style=\"text-align: justify;\">OTHER TYPES OF HYDROGRAPH<\/h4>\r\n<p style=\"text-align: justify;\">A plot of the discharge in a stream plotted against time chronologically is called a hydrograph. Depending upon the unit of time involved, we have<\/p>\r\n<ol style=\"text-align: justify;\">\r\n<li><strong>Annual Hydrograph:<\/strong> It shows variation of daily, weekly or mean flow of any number of successive days over a year.<\/li>\r\n<li><strong>Monthly Hydrograph:<\/strong> It shows the variation of daily mean flow over a month.<\/li>\r\n<li><strong>Seasonal Hydrograph:<\/strong> It shows the variation of the discharge in a particular season such as the monsoon season or dry season.<\/li>\r\n<li><strong>Flood hydrograph or hydrographs due to storm:<\/strong> It shows stream flow due to a storm over a catchment hydrograph 1, 2 and 3 as above are called long term hydrograph and used for long term studies like\r\n<ul>\r\n<li>Calculating the surface water potential of stream<\/li>\r\n<li>Reservoir studies and<\/li>\r\n<li>Drought studies<\/li>\r\n<\/ul>\r\n<\/li>\r\n<\/ol>\r\n<p style=\"text-align: justify;\">Flood hydrograph on the other hand is used to study the flooding characteristics of a stream. It is a short term study.<\/p>\r\n\r\n\r\n\r\n<p style=\"text-align: center;\"><a class=\"btn btn-danger\" role=\"button\" href=\"https:\/\/study.madeeasy.in\/ce\/engineering-hydrology\/what-are-the-components-of-the-runoff\/\" target=\"_blank\" rel=\"noopener\">&lt;&lt; Previous<\/a> | <a class=\"btn btn-success\" role=\"button\" href=\"https:\/\/study.madeeasy.in\/ce\/engineering-hydrology\/risk-reliability-and-safety-factor\/\" rel=\"noopener\"> Next &gt;&gt;<\/a> <br \/><strong> Must Read: <\/strong> <a href=\"https:\/\/study.madeeasy.in\/subjects\/what-is-hydrology-in-civil-engineering\/\" target=\"_blank\" rel=\"noopener\"><strong>What is Hydrology in Civil Engineering?<\/strong><\/a><\/p>\r\n<p>&nbsp;<\/p>\r\n","protected":false},"excerpt":{"rendered":"<p>A number of unit hydrographs can be drawn for a catchment corresponding to different durations. The shape of unit hydrographs<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[120,2],"tags":[149,150,151,152,153],"class_list":["post-450","post","type-post","status-publish","format-standard","hentry","category-engineering-hydrology","category-ce","tag-annual-hydrograph","tag-derivation-of-d-hour-unit-hydrograph-from-iuh","tag-instantaneous-unit-hydrograph-iuh","tag-monthly-hydrograph","tag-seasonal-hydrograph"],"_links":{"self":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts\/450","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/comments?post=450"}],"version-history":[{"count":0,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/posts\/450\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/media?parent=450"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/categories?post=450"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.madeeasy.in\/study\/wp-json\/wp\/v2\/tags?post=450"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}