Editing Lake Manitoba (section)

==Geography==
[[File:NASA Lake Winnipeg.jpg|thumb|left|[[NASA]] image of Lake Manitoba]]
The irregularly shaped lake, about {{convert|200|km}} long, is the smallest of a group of three large lakes, the other two being [[Lake Winnipeg]] (the largest) and [[Lake Winnipegosis]], which are found on the floor of the prehistoric [[Glacial Lake Agassiz]]. The lake is subdivided into two connected but distinctly different basins: a small, irregular-shaped north basin and a much larger south basin. It is part of the watershed of the [[Nelson River]] and [[Hudson Bay]].

The southern tip of the lake, {{convert|24|km}} north of [[Portage la Prairie, Manitoba]], ends in the [[Delta Marsh]], an important staging ground for [[Bird migration|migrating]] birds.

Communities on the lake include [[Fairford, Manitoba|Fairford]], [[Steep Rock, Manitoba|Steep Rock]], St. Laurent, and Sandy Bay.

=== Tributaries and outflows ===
The lake is primarily fed by Lake Winnipegosis to its northwest via the [[Waterhen River (Manitoba)|Waterhen River]], with an average annual contribution of {{convert|1900000|acre.ft|km3|order=flip|abbr=on}}. The [[Whitemud River]] and local overland flow average about {{convert|257,000|acre.ft|km3|order=flip|abbr=on}}. Precipitation contributes about {{convert|1800000|acre.ft|km3|order=flip|abbr=on}}. From 1970 to 2003 the Portage Diversion has contributed an average annual volume of {{convert|246800|acre.ft|km3|order=flip|abbr=on}} from the Assiniboine River. Lake Manitoba drains northeast into Lake Winnipeg through the [[Fairford River]] to [[Lake St. Martin]] and then to the [[Dauphin River]]. The average annual river outflow is {{convert|2030000|acre.ft|km3|order=flip|abbr=on}}.  Average evaporation is {{convert|2020000|acre.ft|km3|order=flip|abbr=on}} per year. Most of the water inflow is from the Waterhen River (42% of the inflow) and from precipitation directly on the lake's surface (40%), while nearly 50% of the outflow is by evaporation.<ref>Volumes provided by Alf Warkentin Manitoba Water Stewardship</ref> This explains its [[Salt lake|hyposaline]] nature.<ref>{{Cite web |url=http://home.cc.umanitoba.ca/~mlast/publications/page1/assets/1988hydrobiol.pdf |title=Archived copy |access-date=2011-07-15 |archive-url=https://web.archive.org/web/20121002025158/http://home.cc.umanitoba.ca/~mlast/publications/page1/assets/1988hydrobiol.pdf |archive-date=2012-10-02 |url-status=dead }}</ref>

=== Water control dam ===
Severe flooding around the lake led to the excavation of an improved outlet channel between 1899 and 1901. In 1933 following dry years in the late 1920s and early 1930s, the Province constructed a concrete control dam across the Fairford River immediately downstream of the channel. A new dam was constructed in 1961. The new structure is operated to try to control levels between {{convert|810.5|and|812.5|ft|order=flip|abbr=on}} above sea level.
{| class="wikitable"
|-
! Period
! Maximum level
! Average level
! Minimum level
! Average annual range
|-
| Pre 1960
|   {{convert|816.25|ft|order=flip|abbr=on}}
|   {{convert|812.17|ft|order=flip|abbr=on}}
|   {{convert|809.92|ft|order=flip|abbr=on}}
|    {{convert|1.4|ft|order=flip|abbr=on}}
|-
| 1960–1999
|   {{convert|813.48|ft|order=flip|abbr=on}}
|   {{convert|811.92|ft|order=flip|abbr=on}}
|   {{convert|810.36|ft|order=flip|abbr=on}}
|    {{convert|1.27|ft|order=flip|abbr=on}}
|}

=== Flood in 2011 ===
Due to above average snowfall over the winter of 2010–2011, and above average precipitation in the spring over the Lake Manitoba watershed, forecasted water levels on Lake Manitoba called for levels above the regulated upper range of {{convert|812.5|ft|order=flip|abbr=on}} above sea level and around the flood stage of {{convert|814|ft|order=flip|abbr=on}} above sea level. With the added inflows of the [[Portage Diversion]] due to high water levels on the [[Assiniboine River]] and its tributaries, of up to {{convert|34,000|cuft/s|m3/s|order=flip|abbr=on}} of water the lake peaked at {{convert|817.2|ft|order=flip|abbr=on}} above sea level on July 21.<ref>Water Survey Canada</ref> On May 31, 2011, when the lake was already very high, {{convert|815.13|ft|order=flip|abbr=on}}, strong winds from the north and the north-west of {{convert|70|km/h|abbr=on}} gusting to {{cvt|90|km/h}} caused major damage to beaches and communities on the south basin of the lake including [[Twin Lakes Beach, Manitoba|Twin Lakes Beach]], [[St. Laurent, Manitoba|St. Laurent]], St. Ambroise, Delta Beach, Lynch Point, Big Point, and large areas of farmland.

===Historical floods===
Unlike a river which can rise and recede relatively quickly, large lakes like Lake Manitoba require months or even years for lake levels to rise and fall. Below are the flood years on record in which Lake Manitoba was above flood stage, as defined by Manitoba Infrastructure and Transportation (MIT), of {{convert|814|ft|order=flip|abbr=on}} ASL. However, beginning around a level of {{convert|813|ft|order=flip|abbr=on}} ASL, localized flooding of agricultural land around the lake can occur.<ref>{{cite web|title=Provincial Flood Control Infrastructure Review of Operating Guidelines: A Report to the Minister of Manitoba Infrastructure and Transportation|url=https://www.gov.mb.ca/mit/wms/wm/pdf/review_operating_guidelines.pdf|publisher=Province of Manitoba|date=August 2015|page=55|access-date=April 24, 2017}}</ref>

{| class="wikitable"
|-
! Year(s)
! Peak lake level (ASL)
|-
! 2011-12
| {{convert|817.2|ft|order=flip|abbr=on}} (2011)<ref>{{cite web|title=Lake Manitoba and Lake St. Martin Outlet Channels Conceptual Design Preliminary Options|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/lmb_lsm_outlet_channel_storyboards.pdf|publisher=Province of Manitoba|date=2014|page=17|access-date=April 23, 2017}}</ref>
|-
! 1881-82
| > {{convert|817|ft|order=flip|abbr=on}} (1882)<ref>{{cite web|title=2011 Flood: Technical Review of Lake Manitoba, Lake St. Martin and Assiniboine River Water Levels|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/assiniboine_lakemb_lsm_report_nov2013.pdf|publisher=Province of Manitoba|date=October 2013|page=40|access-date=April 23, 2017}}</ref>
|-
! 1954-57
| {{convert|816.6|ft|order=flip|abbr=on}} (1955)<ref>{{cite web|title=2011 Flood: Technical Review of Lake Manitoba, Lake St. Martin and Assiniboine River Water Levels|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/assiniboine_lakemb_lsm_report_nov2013.pdf|publisher=Province of Manitoba|date=October 2013|page=25|access-date=April 23, 2017}}</ref>
|-
! 1913
| > {{convert|816|ft|order=flip|abbr=on}}<ref>{{cite web|title=Provincial Flood Control Infrastructure Review of Operating Guidelines: A Report to the Minister of Manitoba Infrastructure and Transportation|url=https://www.gov.mb.ca/mit/wms/wm/pdf/review_operating_guidelines.pdf|publisher=Province of Manitoba|date=August 2015|page=52|access-date=April 24, 2017}}</ref>
|-
! 2014
| {{convert|814.7|ft|order=flip|abbr=on}}<ref>{{cite web|title=Provincial Flood Control Infrastructure Review of Operating Guidelines: A Report to the Minister of Manitoba Infrastructure and Transportation|url=https://www.gov.mb.ca/mit/wms/wm/pdf/review_operating_guidelines.pdf|publisher=Province of Manitoba|date=August 2015|page=23|access-date=April 23, 2017}}</ref>
|-
! 1924
| {{convert|814.2|ft|order=flip|abbr=on}}<ref>{{cite web|title=Lake Manitoba and Lake St. Martin Outlet Channels Conceptual Design Preliminary Options|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/lmb_lsm_outlet_channel_storyboards.pdf|publisher=Province of Manitoba|date=2014|page=4|access-date=April 24, 2017}}</ref>
|-
! 1925
| {{convert|814.2|ft|order=flip|abbr=on}}<ref>{{cite web|title=Lake Manitoba and Lake St. Martin Outlet Channels Conceptual Design Preliminary Options|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/lmb_lsm_outlet_channel_storyboards.pdf|publisher=Province of Manitoba|date=2014|page=4|access-date=April 23, 2017}}</ref>
|}

*In 1881-82 lake levels were not recorded. However, given the topography around Lake Manitoba, a level of {{convert|817|ft|order=flip|abbr=on}} ASL would be required to cause the lake to drain back into the Assiniboine River, which occurred in both 1881 and 1882. Also, a flow of {{convert|14,835|cuft/s|m3/s|order=flip|abbr=on}} was recorded on the Fairford River in 1881, long before significant channel improvements were made. Based on a rating curve for flows on the Fairford River during this period, the flows correlate with a lake level as high as {{convert|817.5|ft|order=flip|abbr=on}} ASL. Furthermore, in his 1890 study entitled "Report of Exploration of the Glacial Lake Agassiz in Manitoba", Warren Upham states that Lake Manitoba rose approximately {{convert|8|ft|order=flip|abbr=on}} above its lowest level, which records show to be around {{convert|810|ft|order=flip|abbr=on}} ASL, suggesting a peak of {{convert|818|ft|order=flip|abbr=on}} ASL.<ref>{{cite web|title=2011 Flood: Technical Review of Lake Manitoba, Lake St. Martin and Assiniboine River Water Levels|url=https://www.gov.mb.ca/mit/floodinfo/floodproofing/reports/pdf/assiniboine_lakemb_lsm_report_nov2013.pdf|publisher=Province of Manitoba|date=October 2013|page=40|access-date=April 23, 2017}}</ref>
*Lake Levels did not begin to be recorded until 1914. However, in 1913 a flow rate of {{convert|11,500|cuft/s|m3/s|order=flip|abbr=on}} on the Fairford River was recorded, which based on a rating curve for flows during this period would correspond with a lake level of greater than {{convert|816|ft|order=flip|abbr=on}} ASL.<ref>{{cite web|title=Provincial Flood Control Infrastructure Review of Operating Guidelines: A Report to the Minister of Manitoba Infrastructure and Transportation|url=https://www.gov.mb.ca/mit/wms/wm/pdf/review_operating_guidelines.pdf|publisher=Province of Manitoba|date=August 2015|page=52|access-date=April 24, 2017}}</ref>
*On May 31, 2011, during a major wind event, Lake Manitoba was measured at {{convert|820.37|ft|order=flip|abbr=on}} ASL at Twin Lakes Beach.<ref>{{cite web|title=Flood Bulletin #68 - June 3, 2011|url=http://news.gov.mb.ca/news/index.html?archive=today&item=11676|newspaper=Province of Manitoba|date=June 3, 2011|access-date=April 23, 2017}}</ref> As a result of the high water level with wind set-up and wave action, significant damage occurred along the south basin of Lake Manitoba. The 2011 peak flood level is the wind-eliminated peak lake level.