{"id":666,"date":"2017-10-12T22:42:51","date_gmt":"2017-10-12T22:42:51","guid":{"rendered":"https:\/\/learn.hydrologystudio.com\/channel-studio\/?post_type=ht_kb&p=666"},"modified":"2017-10-13T16:20:25","modified_gmt":"2017-10-13T16:20:25","slug":"overtopping-flow","status":"publish","type":"ht_kb","link":"https:\/\/learn.hydrologystudio.com\/channel-studio\/knowledge-base\/overtopping-flow\/","title":{"rendered":"Overtopping Flow"},"content":{"rendered":"

Overtopping is automatically computed for bridge and culvert sections and will begin when the headwater, (Hw) rises to the elevation of the roadway or deck as shown in the profile below. 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.<\/p>\n

\"\"<\/p>\n

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 roadway overflow plus the flow through the culvert barrel must equal the total flow. A trial and error process is necessary to determine the amount of the total flow passing through the culvert and the amount flowing across the top chord.<\/p>\n

For Weir, Bridge and Culvert sections, Channel Studio uses the following weir equation:<\/p>\n

\"\"<\/p>\n

Where:<\/p>\n

Q = Overtopping flow
\nCw = Broad crested weir coefficient = 2.66 (1.5) – Bridges, Culverts and Weirs
\nCw = Sharp crested weir coefficient = 3.33 (1.84) – Weirs only
\nL = Crest width
\nH = HGL \u2013 High Chord elevation (The approach velocity is neglected)<\/p>\n

Adjustment for Submergence<\/h2>\n

Weir performance can be affected by submergence, i.e., when the tailwater rises above the weir’s crest and reduces the flow.<\/p>\n

\"\"<\/p>\n

The equation for the reduction in flow is:<\/p>\n

\"\"<\/p>\n

Where:<\/p>\n

Qs = Submerged flow
\nQr = Unsubmerged flow from standard weir equation
\nH1 = upstream head above embankment
\nH2 = downstream head above embankment<\/p>\n","protected":false},"excerpt":{"rendered":"

Culverts with overtopping flow<\/p>\n","protected":false},"author":1,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"footnotes":""},"ht-kb-category":[42],"ht-kb-tag":[],"class_list":["post-666","ht_kb","type-ht_kb","status-publish","format-standard","hentry","ht_kb_category-culverts"],"_links":{"self":[{"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb\/666","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb"}],"about":[{"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/types\/ht_kb"}],"author":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/comments?post=666"}],"version-history":[{"count":2,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb\/666\/revisions"}],"predecessor-version":[{"id":668,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb\/666\/revisions\/668"}],"wp:attachment":[{"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/media?parent=666"}],"wp:term":[{"taxonomy":"ht_kb_category","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb-category?post=666"},{"taxonomy":"ht_kb_tag","embeddable":true,"href":"https:\/\/learn.hydrologystudio.com\/channel-studio\/wp-json\/wp\/v2\/ht-kb-tag?post=666"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}