{"id":1337,"date":"2019-05-06T21:45:50","date_gmt":"2019-05-06T21:45:50","guid":{"rendered":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/?post_type=ht_kb&#038;p=1337"},"modified":"2022-03-07T19:39:15","modified_gmt":"2022-03-07T19:39:15","slug":"weir-and-overtopping-flow-at-headwalls","status":"publish","type":"ht_kb","link":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/knowledge-base\/weir-and-overtopping-flow-at-headwalls\/","title":{"rendered":"Weir and Overtopping Flow at Headwalls"},"content":{"rendered":"\n<p>When an overtopping weir has been added to a headwall junction, the software automatically checks for flow going over the weir.&nbsp;<span style=\"display: inline !important; float: none; background-color: #ffffff; color: #595959; cursor: text; font-family: 'Open Sans','Helvetica Neue',Helvetica,Arial,sans-serif; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;\">Overtopping will begin when the headwater rises to the elevation of the weir crest or roadway. The overtopping will usually occur at the low point of a sag vertical curve on the roadway. The flow will be similar to flow over a broad crested weir. <\/span><\/p>\n\n\n\n<p><span style=\"display: inline !important; float: none; background-color: #ffffff; color: #595959; cursor: text; font-family: 'Open Sans','Helvetica Neue',Helvetica,Arial,sans-serif; font-size: 16px; font-style: normal; font-variant: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: left; text-decoration: none; text-indent: 0px; text-transform: none; -webkit-text-stroke-width: 0px; white-space: normal; word-spacing: 0px;\">It is recommended to have the Check for Inlet Control option checked ON before computing. This is located on the Compute tab.<\/span><\/p>\n\n\n\n<figure class=\"wp-block-image alignnone wp-image-1339 size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"799\" height=\"624\" src=\"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow.png\" alt=\"\" class=\"wp-image-1339\" srcset=\"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow.png 799w, https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow-300x234.png 300w, https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow-768x600.png 768w, https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow-50x39.png 50w, https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow-60x47.png 60w, https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-content\/uploads\/sites\/3\/2019\/05\/OvertoppingFlow-100x78.png 100w\" sizes=\"auto, (max-width: 799px) 100vw, 799px\" \/><figcaption>Note that overtopping flow is not elegible as Carryover Flow to other inlets. Overtopping flow always returns to it&#8217;s originating line at the downstream end.<\/figcaption><\/figure>\n\n\n\n<p>It is a simple matter to calculate the flow across the roadway for a given upstream water surface elevation using the weir equation. The problem is that the weir overtopping flow plus the pipe flow must equal the total flow. A trial and error process is necessary to determine the amount of the total flow passing through the pipe(s) and the amount flowing across the weir at the same energy grade line.<\/p>\n\n\n\n<p>Stormwater Studio uses the following broad crested weir equation:<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/learn.hydrologystudio.com\/culvert-studio\/wp-content\/uploads\/sites\/4\/2017\/10\/EqBroadWeir.jpg\" alt=\"\" class=\"wp-image-323\"\/><\/figure>\n\n\n\n<p>Where:<\/p>\n\n\n\n<p>Q = overtopping flow in cfs (cms)<br>Cw = broad crested weir coefficient = 3.09 (1.50)<br>L = crest width in ft (m)<br>H = Hw \u2013 Weir Elevation in ft (m)<\/p>\n\n\n\n<p>As the depth of the overtopping flow increases the weir crest is extended upwards.<\/p>\n\n\n\n<p><em><strong>IMPORTANT:<\/strong><\/em>\u00a0Weir flow is not eligible to be used as carryover flow to other inlets. Rather it rejoins the pipe flow at the downstream end. From there the total Q will move to the next downstream Line as usual. A Bypass Target Line cannot be specified.<\/p>\n\n\n\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Describes how overtopping flow is calculated at headwalls with optional weir<\/p>\n","protected":false},"author":1,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"footnotes":""},"ht-kb-category":[21],"ht-kb-tag":[],"class_list":["post-1337","ht_kb","type-ht_kb","status-publish","format-standard","hentry","ht_kb_category-computational-methods"],"_links":{"self":[{"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb\/1337","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb"}],"about":[{"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/types\/ht_kb"}],"author":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/comments?post=1337"}],"version-history":[{"count":9,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb\/1337\/revisions"}],"predecessor-version":[{"id":2364,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb\/1337\/revisions\/2364"}],"wp:attachment":[{"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/media?parent=1337"}],"wp:term":[{"taxonomy":"ht_kb_category","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb-category?post=1337"},{"taxonomy":"ht_kb_tag","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/stormwater-studio\/wp-json\/wp\/v2\/ht-kb-tag?post=1337"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}