Hydrology

2020

  • note: we also record the water levels at Goward Road bridge most weeks, when gardening.
  • see our Whitehead Park photos for those records
  • Update re Garth van der Kamp:
    •  Research Associate
      Global Institute for Water Security
      University of Saskatchewan


“This graph shows the changes of the water level of Prospect Lake from September 2018 until August 2020. The level is measured with a staff gauge at the Goward Road bridge. The water levels are shown relative to the top of the weir that controls the outflow from Prospect lake to Tod Creek. The higher the water level above the top of the weir, the greater is the outflow.

After heavy winter rains the water level of the lake can rise as to as much as 0.76 meters (3.5 feet) higher than the top of the weir, as happened early in 2020. On that day the flow over the weir was about 3 cubic meters per second. In summer the water level of the lake declines due to evaporation. When the lake level drops below the top of the weir the flow to Tod Creek becomes a trickle of 1 or 2 Liters per second. By itself n outflow at that rate would only drop the lake level by 2 or 3 cm over the summer. The water loss from the lake by evaporation can drop the water level by as much as 50 cm during a dry hot summer, as in 2018. So the summer-time drop of the water level is almost entirely due to evaporation from the lake.

The rains usually start again in October, but it takes a lot of inflow to the Lake to refill it to the top of the weir. The water level in Durrance Lake, the other main source of water to Tod Creek, follows a similar pattern. So strong flow down Tod Creek does not occur again until December in most years. This means that coho salmon have to wait until December before they can swim up from Tod Inlet to spawn in Tod Creek.”


Keeping track of water levels and flow at the Goward Rd bridge. The graph below shows the water level at the staff gauge, reported as height above the top of the weir. The staff gauge readings taken during the water quality testing are an important part of that record.

This year the water level of Prospect Lake has remained well above the weir, presumably due to the cool and wet weather of May and June, and the flow into Tod Creek out of the lake also persisted quite well. In the past week the water level has started to drop and the flow to the creek is now very low and may soon stop altogether as the lake level declines below the top of the weir. Outflow from Killarney and Durrance Lakes are probably following a similar pattern.

Garth van der Kamp:  Emeritus scientist, Water Science and Technology, Environment and Climate Change Canada


Here’s some photos of Tod Creek at high flow:
one of the Creek just above its mouth (2018 12 13) which is the creek at the same location as the photo of Gwen van der Kamp measuring the flow with a small plastic pipe a few months earlier

[see ** Sept 7/ 2018 below for the original photo plus text]:

 

 

 

**

 

 

 

 

 

 

 

 

 

 

 

The other two photos are of the staff gauge at Goward Bridge during the peak flow on Feb 1, 2020 when the staff gauge was almost submerged. These make quite a contrast with the photos of the staff gauge at low flow.

 


 2019

The Team: Michael Derry, Winona Pugh, Garth van der Kamp, Mary Haig-Brown

 

Meadowbrook site for hydrology testing, Jan 5/ 2019.

 

Tod Creek at Goward Road site, Jan 5/ 2019.

 

 

 

 

 

 

 

 

Water gauge, Jan 5/ 2019.

 

Closer view of water gauge, Jan 5/ 2019.

 


2018

Tod Creek Water Gauge: Goward Road bridge

Oct 22/ 2018

Oct 22/ 2018

 

Water gauge on the right, looking south toward Prospect Lake from under the Goward Road bridge. Oct 22/ 2018

Photo taken from WHP-east, on Goward Road looking toward Prospect Lake Road. Oct 22/ 2018

 


Tod Creek Water Gauge: Goward Road bridge

Oct 15/ 2018


Tod Creek Water Gauge: Goward Road bridge

The staff gauge is read like a vertical measuring tape using the metric system. The gauge is set at the creek bottom so measurements show depth to the bottom of the creek (ie: creek water depth). The top of the black lines are even numbers.

Sept 24/ 2018


Tod Creek: lower creek, below the fishway

Tod Creek Flow Measurements Sustain Fry in Drought Conditions by Garth van der Kamp

** Photo for 2020 comparison

Sept 7th, 2018: This photo shows all the flow in Tod Creek channeled through the piece o plastic pvc pipe we brought along. To stop most of the leakage around the pipe we squeezed in bits of moss around the pipe. That way the flow can be measured quite accurately by timing how long it takes to fill a small container. In the photo Gwen is holding a watch in her other hand, for timing. To get a flow measurement she would count down “3,2,1, now” and at “now” I would catch the flow in the 500 mL bottle shown in the photo and call out “stop” when it is nearly full. As it turned out, the flow was stronger than I had previously estimated and it took only 4 seconds to fill the container. We should have brought a larger bottle, such as the 1L milk bottle that Bernie brought along later to do measurements of flow in Meadowbrook Creek.

This measurement of 8L/minute was taken in Tod Creek about 100 m upstream from the creek mouth in Tod Inlet. The small pools right where we did the measurement had several small fish, likely coho fry. Where the creek flows between boulders in its rocky bed the flow seemed like hardly even a trickle. So a flow equivalent to what a lawn sprinkler uses is enough to keep the little salmon alive in a creek.

It is important to note that the measurement was taken on the morning of Sept 7 [2018] just before that first showers started in the afternoon. The last significant rain occurred on June 30 [2018], so this was the flow in Tod Creek after more than 2 months of drought. I’m not sure how extreme this summer’s drought was compared to other years, but judging by the distressed state of trees on the dry uplands at Gore Park, this drought was especially severe.

Emeritus scientist, Water Science and Technology, Environment and Climate Change Canada

 

Sept 18th, 2018

Someone responded that looking at the above photo it seems like an awfully small flow for a “creek”. But maybe that is just the point: that a flow of just a few L/min can be sufficient to maintain the pool/stream habitat for salmon fry during severe droughts. And so maybe the concerned residents around Prospect Lake need not be quite so worried that the lake would be drained just to keep a few fish alive in Tod creek. Based on a lake area of 74 hectares and a lake evaporation loss of 5mm/day (for a typical summer day) the lake loses about 2500 L/minute, averaged over 24 hours, by evaporation, so releasing say 10L/min to maintain flow in Tod Creek would not even be noticeable. Even over a whole summer (100 days) such a release, amounting to 1 acre-foot, would only lower the water level of the lake by 2 mm.

Even a release of 100L/min would only lower the lake level by only 2 cm over a summer. Such a release would likely suffice to offset water losses from the creek to riparian vegetation, and maintain flow and aerated pools in Tod Creek all the way past Tod Flats and to the fishway.

Comments are closed.

error: Content is protected !!