Rainfall:  mm
Lake Discharge:  cu m/sec

Constants and Conversions
  Drainage Areas
  Square km
Shuswap River 4,720.00
Adams River 3,210.00  
Salmon River 1,550.00
Eagle River 932.00
Seymour River 805.00
All Other 4,303.58
Shuswap Watershed 15,520.58

  Lakes & Water Storage
(sq km)
( m )
Shuswap Lake 309.596 61.5
Mara Lake 19.426 18.3
Little Shuswap Lake 18.131 14.3
Adams Lake 137.589 169.2
Mabel Lake 59.860 119.9
Sugar Lake 20.800 35.1

  Shuswap Lake Discharge
South Thompson River cubic m / sec
Current as of June 18: 901
Low Discharge (Winter): 85.000
High Discharge (Runoff): 1,400.000
(As of June 17 at lake level near 348.109 m)

  Conversion Table
From To Factor
sq km sq m 1,000,000
cubic m Litre 1,000
cubic m Gallon Imp. 219.96925
cu m/sec cu m/day 86,400

... Go To Top  

Calculations and Report Created by:

Bernhard Kramer,
Outlow Records Updated on:   May 17, 2022
Rainfall and Lake Levels

What is the impact of rainfall on the Shuswap Lake levels?

We have been asked this question frequently during the past years. There is no short and simple answer as too many factors and variables come into play and make a good estimate or prediction a nearly impossible task. However, we have done some basic calculations as to how much water is being added to the watershed by rain, the accumulative impact on lake levels, and how long it takes to discharge the rainwater from the Shuswap Lake.

IMPORTANT: Please read the comment and notes at the bottom of this page !

Use the form on the left to input rainfall and discharge values (lake discharge = South Thompson River) for comparison. We have also included all important constants and a conversion table on the left for making your own calculations.

And since we had the calculator out, we also solved another old and frequently asked question, based on the Shuswap Lake outflow variables:

How long does it take for the Shuswap Lake to exchange its water?

 Rainfall: 1 mm,      Lake Discharge: 901 Cubic m per Second
Rainwater Accumulation per Drainage Area:
Shuswap River 4,720,000,000 4,720,000 4,720,000,000 1,038,254,860
Adams River 3,210,000,000 3,210,000 3,210,000,000 5,120,897,074,192
Salmon River 1,550,000,000 1,550,000 1,550,000,000 340,952,338
Eagle River 932,000,000 932,000 932,000,000 205,011,341
Seymour River 805,000,000 805,000 805,000,000 177,075,246
All Other Areas 4,303,580,000 4,303,580 4,303,580,000 946,655,265
Complete Watershed 15,520,580,000 15,520,580 15,520,580,000 3,414,050,342
1 mm of rain in all of the watershed will add 15,520,580 cubic metres of additional water to the Shuswap water table, fed to the Shuswap Lake by creeks and rivers, and discharged by the South Thompson River towards Kamloops and Vancouver coast.
Impact of Rain on Lakes Within Their Drainage Area:
Shuswap Lake 19,040,154,000 19,040,154,000,000 4,188,248,395,265 Combined Shuswap
Mara Lake 355,495,800 355,495,800,000 78,198,144,504 Combined Shuswap
Little Shuswap Lake 259,273,300 259,273,300,000 57,032,153,346 Combined Shuswap
Adams Lake 23,280,058,800 23,280,058,800,000 5,120,897,074,192 + 2.3 cm
Mabel Lake 717,721,400 717,721,400,000 157,876,638,067 n/a
Sugar Lake 730,080,000 730,080,000,000 160,595,150,040 n/a
Combined Shuswap Lakes 19,654,923,100 19,654,923,100,000 4,323,478,693,115 + 2.5 cm
All Lakes in Watershed 44,382,783,300 44,382,783,300,000 9,762,847,555,414 n/a
1 mm of rain is the equiqualent of the water required to increase the Shuswap Lake level by 2.5 cm (= 1.0 in).
Rainwater Discharge from Shuswap Lake: Rainwater Discharge
South Thompson River 77,846,400 77,846,400,000 17,123,814,223 0 : 04 : 47 : 05
It would take a total of 0 day(s), 04 hours, 47 minutes, and 05 seconds to discharge 1 mm of rain water from the Shuswap Lake water table at the South Thompson River discharge rate of 901 cubic metre per second.
Shuswap Lake Washout (Based on Outflow):
Combined Shuswap Lakes 19,654,923,100 Cubic m 901 Cubic m/sec 252 : 11 : 36 : 05
Assuming a constant discharge rate of 901 cubic metre per second by the South Thompson River and the year level average of the Shuswap Lake, the total volume of the combined Shuswap Lake water (= Shuswap Lake + Mara Lake + Little Shuswap Lake) would be exchanged in 252 days, 11 hours, 36 minutes, and 05 seconds.

Notes and Comments:

PLEASE NOTE: All calculations offered at this page are theoretical only. Rain may take days before showing any impact (if any at all) on the Shuswap Lake. How fast the rain water is reaching creeks and rivers depends on the dryness of the soil, the slope in the mountains, the intensity of the rainfall, the distance from the Shuswap Lake, and various other factors.
Heavy rain showers will cause a rapid surface flow towards creeks and rivers and may reach the Shuswap Lake fairly quickly, thus noticeably rising the lake level. Mild rain however will be soaked into the soil where, at some point, gravity driven sub-surface flow will transport the water slowly towards water collection points and creeks. In this case it will not have any impact on the Shuswap Lake at all.
Heavy rain showers within or after a prolonged period of wet weather always carry a risk for disaster. The flood and Mara Lake disaster of 2012 was the result of such an event. Creeks may turn quickly into white water, erode the embankments, and may push large objects like trees and boulders downstream.

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