Water in Otter Lake is supplied from an extensive drainage area (10,000 acres or more) via at least 10 small parent streams most of which feed into the lake via its numerous wetland areas. Because Otter Lake abuts the Smiths Falls and area limestone plain there are also several natural springs, the location of which and the volume of water they produce are unknown. However Otter Lake has only a single outlet, Otter Creek. Since the 1960's beavers have been quite active in the upper reaches of the creek. RVCA estimates that there are at lest 8 beaver dams between Otter Lake and Lombardy. All of these dams reduce the flow of water in Otter Creek, however only 2 or 3 dams downstream from the culvert on Otter Lake Road have significant effect on water levels in Otter Lake. As a result, beaver activity in the creek combined with the large volume of water resulting from the early spring runoff can often have a significant effect on the water level in the lake. Water levels are often quite high in the early spring, especially if there has been a rapid spring thaw. These high water levels can cause local flooding to private access roads and low lying properties, which is obviously a serious concern to some property owners. After the spring runoff is complete the lake level usually drops significantly over the course of a normal summer, with most of the water loss resulting from evaporation and lack of inflow. Water levels can again rise in the fall, when beavers again become active in the creek, however following the freeze over, the lake level will drop during the winter months

Control of Water Levels
     In 2000, an attempt was made to control the water flow in the creek by the installation of "beaver bafflers" in the beaver dams in the upper reaches of Otter Creek. A "beaver baffler" is essentially a tube inserted through the base of the beaver dam. OLLA supported, and participated in beaver baffler installation, however, the bafflers were not successful, primarily because they required continual maintenance. OLLA measures, records and communicates water levels to the Rideau Valley Conservation Authority (RVCA) and Otter Lake Landowners’ Association (OLLA) members. OLLA does not undertake any effort, either alone or in concert with any other party, to control or manipulate the water level on Otter Lake..

Water level monitoring
     OLLA has accurately measured water levels since 2003. The water level is measured several times a month at a site on the Lake Steward’s property that has been calibrated by RVCA at 124.91 metres above sea level (MASL) or, during the winter months at the culvert on Otter Lake Road that has also been calibrated by RVCA. The graph below shows water depth in Otter Lake from January 2005 to the present. The “error bars” in red indicate maximum and minimum water levels for the month. The green reference line represents the median water level of 124.81 MASL and the upper reference lines represent RVCA’s estimated 1:2 and 1:100 year flood level respectively. The graph clearly indicates how water levels can fluctuate quite dramatically. In the spring of 2005 the water level was moderately high, however the lake level dropped almost half a metre between April and September. The summer of 2005 was incredibly hot and dry with virtually no rain in June, July and August. In addition beaver dams in the upper reaches of the creek were destroyed and beavers were removed from the creek. Hence, there was increased outflow of water from the lake that could not be replenished and there was extensive water loss by evaporation. It should be noted that this activity in Otter Creek was NOT initiated NOR supported by OLLA, however since the Association does not have policing powers, there is little that can be done if individuals, whether they be Otter Lake property owners or from elsewhere, choose to take it upon themselves to trespass on private property for the purpose of removing dams and/or beavers.
In 2007 RVCA implemented (on a trial basis) a Beaver Management Program. In June of 2007 and in response to concerns/complaints received from property owners regarding flooding of property and access roads, RVCA proposed the following action. "In an effort to balance the aquatic ecosystem needs and landowner flooding issues it is recommended that Dam #1 and #2 in the upper reaches of Otter Creek be breeched in the centre of the dam. The following mitigation measures will be implemented during beaver dam removal activities. Breeching of the beaver dam will be carried out in a manner that minimizes downstream sediment load. Breeching of the beaver dam will occur during low flow conditions and on days when rain is not expected. Only a small portion of the dam will be pulled back at one time to allow the water from the beaver pond to be released slowly. As water levels decrease, the size of the opening may be increased to allow complete drainage of the retention area. Work is to be completed by hand with NO heavy equipment on the bed of Otter Creek at any time. Areas downstream of the beaver dam will be monitored during breaching activities to determine whether damage to the channel and adjacent properties receiving additional water volumes are occurring. Fish that become trapped in isolated pools as a result of beaver pond de-watering will be relocated to the main channel of the watercourse. Dam building nuisance beaver for Dam #1 and #2 will be trapped using appropriate trapping methods".
     All property owners should be aware that all of the above actions to lower lake levels were solely an RVCA initiative. OLLA did NOT make any requests to RVCA regarding water levels. OLLA was kept informed and consulted by RVCA during the period the Beaver Management Program was in place. However, the program ended in 2010 but as can be seen from the water level graph above, water level fluctuations were quite modest during the period the program was in place. Nonetheless, the RVCA 1:2 year flood level was exceeded in 2008 (when we had a winter with record snowfall) indicating that natural events are the main cause of water level fluctuations. The 1:2 year flood level was exceeded again in the Spring of 2014

Current Water Level Situation
     The winter of 2014 -2015 produced quite a lot of snow and extremely cold temperatures. Otter Lake was totally frozen over by January 11. In fact the temperatures recorded in February were the coldest on record, however as a result the snow was very dry with little water content. In contrast to 2014, the Spring thaw was quite gradual an water levels were not exceptionally high, so flooding of low-lying properties and access roads would have been minimal. In fact RVCA issued a moderate drought conditions warning for the entire Rideau valley watershed in April that was not lifted until early June. Water levels were relatively stable during the Summer months but dropped a little in the Fall. In 2015 the "ice off" occurred on April 21. As a result of the very cold temperatures in February, Otter Creek was frozen over for some time, Given that we had more rain than snow in November and December and the fact that the little snow we did get melted, the lake level rose somewhat by January 2016. The lake was finally completely frozen over by January 21. Otter Creek remained open and flowed well all winter.
     The graph on the right shows the lake level from January 2016 to the present. Again the “error bars” represent maximum and minimum water levels for each measurement period. The yellow reference line on the graph indicates the median water level of 124.82 MASL and the green reference line represents RVCA’s 1:2 year flood level. The graph also includes rainfall amounts since the latter has a very significant effect on water levels.
     The winter of 2015 -2016 gave fluctuating temperatures and was no where near as cold as the winter of 2014-2015. The early winter was quite mild with more rain than snow until January, hence the relatively high water levels in January. Most of the winter's snow came in February with one major snowstorm of 50cm! Mild weather in March during which most of the snow melted resulted in an early spring thaw. As a result our spring high was in late March and early April and water levels were quite high and would have resulted in some flooding, except the high occurred while the lake was still frozen. The "ice off" in 2016 was on April 5 so the lake was frozen for a relatively short period. After April the drought began. RVCA issued a drought conditions advisory in May and expanded that to a moderate to severe drought condition statement in late June for the entire Rideau valley watershed. This statement was increased to severe in August and remained in effect until December when it was downgraded to “moderate”. It explains why our water levels dropped so significantly since April. There was little or no flow in Otter Creek throughout the summer and virtually all of our inflow streams were dry. The total rainfall for the summer of 2016 was less than 300 mm whereas in 2015 it was almost 600 mm. Also we had 15 days of temperatures above 30 degrees Celsius in 2016, more than three times the number of +30 degree days we had in 2015. On a +30 degree day the evaporation rate for a lake can be as high as 2.5 cm (1 inch). With the rain and snow we received in October and November there has been some recovery in water level as can be seen from the graph above. RVCA’s drought conditions statement was downgraded to minor in mid January, 2017. Therefore, water level recovery will occur over the winter so long as there is mild weather with a lot of rain or a cold winter with a higher than average snowfall accumulation!! Fortunately that seems to be what is happening. In fact with the early snowmelt and recent heavy rains, the water level is currently extremely high and RVCA, MNRF and FOCA issued flood warnings for the entire area in mid April and have re-issued the warnings for early May. RVCA states that "All of the dams in the system have been adjusted to allow as much water as possible to pass through. However, the levels on many of the lakes in the upper watershed are high causing shoreline flooding, access issues, erosion and damage to structures. It is expected that it will take some time to return to normal levels once a peak is reached. As the flood waters rise, so too does the hazard level. Flooded roads are dangerous to drive and walk on and moving water and slippery streambanks are not good places for anyone to be. Parents need to inform children about the dangers"..

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