Stream Flow

Updated June 2021 based on data available through December 2019.

Declining Trend

Since 1975, 8 of the 17 rivers that were monitored and studied by programs on both sides of the international border showed significant decreasing summer flow trends. 8 of the remaining 9 rivers showed only minor increases or decreases in flow.

On this page:

About Stream Flow

Low flow in our streams and rivers occurs during summer months when there is less rain and warmer temperatures and the snow-pack has been depleted through spring melt.

The Salish Sea is an ecosystem defined by the movement of water. Freshwater begins as rain or snow in the Cascade and Olympic mountains. It flows in streams down through fertile valleys and into a complex network of salt marshes, wetlands, and bays.

For this indicator, we analyzed trends in summertime stream flow to examine potential impacts to aquatic ecosystems, water supply, and other systems that depend on summer low flows. The summer months coincide with seasonally dry and warm climate conditions when mountain snow-packs are generally depleted.

Changes to summer low flow systems may adversely impact salmon runs, wildlife, and our residential, agricultural, and industrial water supplies.

How do we measure low flows?

Summer low flow is calculated as the minimum 30-day average water flow measured each year at river and stream gauging stations.

We collected data since 1975 to determine whether the long-term trends of annual summer low flow levels are declining or increasing in unregulated rivers. Unregulated rivers are those without major dams or constructed reservoirs and are most sensitive to climate and land-use changes.

What's Happening?

Since 1975, 8 of the 17 rivers studied by Environment and Climate Change Canada, EPA, and other partners showed significant decreasing summer flow trends. 8 of the remaining 9 rivers showed weaker trends of either increasing or decreasing flows over the 43-year study period (see chart and map below).

The remaining river, the Puyallup River, showed a strongly increasing flow trend. The Puyallup River has upper tributaries fed by glaciers and snowfields high in the mountains, specifically Mount Rainier. The increased flow in this river may be due to glacial melting and recession.

However, increasing flows due to glacial recession should be understood as a temporary increase in flow. As the glaciers recede, they will not be able to sustain these additional flows in late summer.

In addition, the low-flow seasons occurring in 2015-2016 were the same years as a strong "El Niño" weather pattern that causes warmer weather with often with less precipitation in certain areas. This weather pattern has the potential to cause lower flows for those years contributing to a declining trend.

Chart showing average annual change in 30-day minimum low flows in Salish Sea rivers since 1975.
Average annual change in 30-day minimum low flows in Salish Sea rivers since 1975. Click chart for larger view.
Salish Sea rivers showing improving (green) or declining (red) summer stream flows since 1975. Click map for larger view.

Sustainable Perspective

Shallow groundwater wells withdraw water from the same aquifers that replenish wetlands and recharge streams.

In the Dungeness and Elwha River basins between 1986 and 2006, the number of wells increased by 275% while the population grew by only 28%. The average depth of these wells before 1986 was 114 feet, but new well depth increased to an average of 145 feet by 2006.

Population in the Dungeness and Elwha River basins is expected to grow by an additional 30% by 2026, suggesting a potentially unsustainable trend for water use. However, a water resource management rule was recently adopted to prevent further declines in flow resulting from ground water withdrawals.

In January 2018, the Washington state legislature enacted Senate Bill 6091 that established the Dungeness area as one of two groundwater metering pilot projects. The goals of the pilot are to:

  • Determine the overall feasibility of measuring water use for all new groundwater withdrawals.
  • Address technical, practical, and legal considerations.
  • Identify the costs and benefits of a water management program relying on meters versus one that estimates permit-exempt groundwater withdrawals.
  • Ensure accurate data collection.

Why Is It Important?

If summer flows continue to decline as demand for water continues to increase for uses such as drinking water and irrigation, there is potential for conflict between human and ecosystem needs. Low water flow is already a priority issue for salmon in 14 of the 19 Puget Sound Water Resource Inventory Areas.

Changes in stream flow are associated with shifts in salmon habitat, water temperature increases, nutrient availability, and sediment levels. These changes can impact both human uses and the life cycles of salmon and other aquatic life.

From Too Much to Not Enough: Rain and Snow Patterns in the Koksilah and Cowichan Rivers

The Koksilah and Cowichan Rivers in British Columbia (BC) are examples of how changing rain and snow patterns are affecting people living in the Salish Sea.

The need to build resilience to floods and droughts is one of the top 5 water challenges that will define British Columbia’s futureaccording to the POLIS Project on Ecological Governance. The challenge is a big one, according to a January 2020 interview with a biologist from the Cowichan Tribes First Nation on CBC Radio:

"It's simple math. If you don't have that huge volume of rain that we're used to coming at the time we are used to, it starts to impact ecosystems."

In the fall of 2009, the Cowichan and Koksilah rivers flooded their banks and caused evacuations in nearby communities. In response, municipal officials declared a state of emergency that remained in place until floodwaters receded. Extreme flooding in the Cowichan River area caused problems again in the winter of 2020.

Fall floods are not the only trouble for the Cowichan and Koksilah rivers. The spring and summer river levels are vital to salmon success too. Low water levels during the spring and summer months can prevent juvenile salmon from reaching the ocean and in some years have prompted local community efforts to help the young salmon reach their destination. During the summer of 2019, water levels were so low that the Province of BC restricted water use.

In January 2020, the BC Ministry of Environment and Climate Change Strategy announced that monitoring wells will be installed in the Koksilah River watershed to watch for serious declines in water levels during drought conditions.

Why Is It Happening?

Rainfall and snowmelt are the primary sources of water for rivers and streams in the Salish Sea, but many other factors can also impact stream flows, including:

  • Dams and other hydrological modifications.
  • Loss and change of vegetative cover.
  • Surface and ground water withdrawals for municipal, domestic, commercial, industrial, and agricultural water supplies.
  • Wells that tap ground water.
  • Over-allocation of water rights.
  • New buildings, roads, and parking lots that prevent water from infiltrating into the ground and slowly recharging streams throughout the summer.

Climate Modeling

Climate models suggest that over the next four decades, rainwater runoff will become more important than snowmelt for recharging our freshwater streams in mountainous watersheds like those surrounding the Salish Sea. Higher daily temperatures will shorten the overall snowfall season and accelerate the rate of spring snowmelt, leading to earlier, greater, and more rapid late-fall and early-spring runoff and lower summer flows.

Assessments by the University of Washington’s Climate Impacts Group suggest that climate change pressures in Puget Sound are likely to include:

Changes in streamflow timing and volume. Watersheds with streamflow based mostly or partially on snowmelt are projected to have the greatest hydrological shifts associated with climate change.

Temperature changes. During the last century, average air temperature in the Puget Sound region increased 2.3°F (1.3°C). Average annual temperature in the Pacific Northwest is projected to increase by about 2°F (1.1°C) by the 2020s, 3.2°F (1.8°C) by the 2040s and 5.3°F (2.9°C) by the 2080s (relative to the period from 1970-1999).

For the Georgia Depression eco-province, consisting of Southeastern Vancouver Island, the Gulf Islands and the Lower Mainland, from 1900 to 2013, the temperature increased 0.8°C (1.4°F). For all of BC, the predicted warming is 1.7°C (3.1°F) to 4.5°C (8.1°F) by the end of the 21st century, compared to the 1961-1990 historical average. Most models also project wetter winters and drier summers for both Puget Sound and Georgia Basin.

Loss of snowpack and glacial retreat. The loss of snow-pack and glacial retreat are one of the most far-reaching impacts of rising temperature. It affects water availability for both people and wildlife. Under a moderate warming scenario (the A1B greenhouse emissions scenario presented by the Intergovernmental Panel on Climate Change), average spring snow-pack in Washington is projected to decrease 29% by the 2020s, 44% by the 2040s, and 65% by the 2080s (relative to the average for 1916-2006).

In the Georgia Depression eco-province, snow-pack depth decreased by 6% per decade from 1950-2014 but with no change in snow water content. From 1900-2009 the North Cascades snow-pack retreated 56% while the Olympic Mountains snow-pack declined 34%. This threatens an important water source as 10% to 44% of total summer stream flow for the North Cascades originates from glaciers, depending on watershed. Glaciers in the Georgia Depression ecozone are primarily on Vancouver Island where the greatest percent loss occurred for the whole province, which for B.C. all together decreased by 2525km2 (975 square miles).

Primary Sources of Water for Salish Sea Rivers

River Primary Snow Source Glacier Source
Nooksack River (at Ferndale, WA) Rain and snow-fed Mt. Baker
North Fork Stillaguamish River (near Arlington, WA) Rain and snow-fed Cascades
Puyallup River (near Orting, WA) Rain and snow-fed Mt. Rainier
Snohomish River (near Monroe, WA) Rain and snow-fed Cascades
Dungeness River (near Sequim, WA) Snow-fed Olympics
Lillooet River (near Pemberton, B.C.) Snow-fed

Lillooet Icecap

Lillooet River glacier cover changes over time:
1985 = 19.9%
2005 = 17.5%
2013 = 16.3%
Nahatlatch River (below Tachewana Creek, B.C.) Snow-fed

Nahatlatch Glacier

Nahatlatch glacier cover changes over time:
1985 = 2.06%
2005 = 1.69%
2013 = 1.62%
Oyster River (below Woodhus Creek, B.C.)

Rain and snow-fed*

*Glacier signal is extremely minimal (anything under 2% glacier cover and the glacier signal is not significant).

Oyster River Glacier

Oyster River glacier cover changes over time:
1985 = 0.13%
2005 = 0.10%
2013 = 0.06%

What's Being Done About It?

Streams and rivers are being closely monitored to help forecast low flow conditions. Actions that are already underway in both Canada and the U.S. that will help address this complex issue include water conservation programs, promoting sustainable development, and long range planning.

Below are some examples of projects that are being implemented to help address decreasing stream flows.

The following links exit the site

Georgia Basin

Improve long term projections and planning. Actions by Environment and Climate Change Canada have focused on monitoring, modeling and research to support long term planning and management for anticipated low stream flows exaggerated by climate change.

  • Adapting to increased peak flows that occur because of shifts in the hydrology including the change of timing and intensity of flow. Potential strategies include considering precipitation pattern changes when planning clear-cut areas, account for increased natural disturbance in these clear-cut areas, reducing forest road densities, designing infrastructure for flooding, and avoiding development on floodplains.
  • Adapting to longer low flow periods that lead to potential water shortages for agriculture. One strategy of the City of Delta is storing precipitation. Stored water can be used as the main water source for smaller farms or an emergency backup for larger farms during the drier summer months.
  • Adapting to salmon habitat change due to shifted streamflow patterns. A potential strategy is maintain high-quality habitat to improve resilience and minimize cumulative effects from anthropogenic forces.

Modernize water laws. As one of the commitments under its Living Water Smart plan, the British Columbia Ministry of Environment and Climate Strategy is in the process of modernizing its water laws to address stream flow needs for competing uses and to protect groundwater. One of these laws, the Water Sustainability Act, came into effect on February 29, 2016. Under this law is the Groundwater Protection Regulation, which ensures actions relating to wells and groundwater are environmentally friendly.

Monitor flow conditions. The British Columbia Ministry of Forests, Lands and Natural Resource Operations and Rural Development operates the River Forecast Centre which interprets streamflow data along with snow and meteorological data from other agencies to inform about upcoming streamflow conditions.

Promote sustainable development. Regional governments such as the Capital Regional District, Metro Vancouver and the Fraser Valley Regional District, and their member cities are developing long range growth plans (called Official Community Plans) to help ensure that we will be able to meet future water use needs. For example, the City of Surrey has a plan to maintain base stream flows and natural water flow patterns to protect aquatic animals and avoid flood damage.

Puget Sound

As a result of flow monitoring in rivers in the Puget Sound basin, the following general objectives have been identified for river management:

  • Maintain flows in unregulated rivers that currently are most stable: Puyallup, Dungeness, Nooksack.
  • Restore low flows to bring the Snohomish River from a weakly decreasing trend to a neutral trend; and to bring the Deschutes River, North Fork Stillaguamish River, and Issaquah Creek from a strongly decreasing trend to a weakly decreasing trend.

Agencies are using the following approaches to help achieve these objectives:

Establish and update instream flow rules and manage future water withdrawals from rivers and streams. The term “instream flow” is used to identify a specific stream flow (typically measured in cubic feet per second) at specific locations for defined time periods. Instream flows are usually defined as the stream flows needed to protect and preserve instream resources and values, such as fish, wildlife, water quality, aesthetics, and recreation. Indirectly, instream flow rules can also help us know where to target flow restoration projects, like conservation. The Washington Department of Ecology has adopted rules protecting stream flows in 15 out of 19 Puget Sound watersheds.

Decrease water use. Managing demand and promoting conservation will be critical as population increases. The near-term objectives for water demand and water conservation address four key sectors: municipalities, agriculture, industry, and rural domestic water users. Demand and conservation goals will be met through a combination of implementation and enforcement of rules, voluntary participation in conservation programs, market-based approaches to adjust water usage, and current and emerging water conservation technologies.

Improve groundwater management. A critical approach to protection and restoration of freshwater resources includes management of groundwater along with surface waters to better account for the interaction between the two. Chapter 173-200 of Washington’s Administrative Code establishes groundwater quality standards to protect sources from pollution.

Promote reclaimed water projects. Reclaimed water comes from domestic wastewater and small amounts of industrial process water or stormwater. The process of reclaiming water - sometimes called water recycling or water reuse - involves a treatment process that speeds up nature's restoration of water quality. The process provides a high level of disinfection to assure that water meets stringent requirements. Reclaimed water can be used for irrigation, industrial processes, toilet flushing, dust control, construction activities, and many other non-potable uses. Reclaimed water also can be used as resource to create, restore, and enhance wetlands, recharge groundwater supplies, and increase the flows in rivers and streams. The first reclaimed water rule came into effect February 23, 2018.

Learn More

Learn more about stream flow and some of the work our partners are doing.

Five Things You Can Do To Help

  1. Fix your leaks! An average home can waste more than 10,000 gallons of water every year due to running toilets, dripping faucets, and other household leaks. Visit EPA's Fix a Leak Week page for tips on where to look for leaks.
  2. Consider water efficiency next time you buy new products like washing machines, dishwashers, refrigerators, taps, and toilets. Check out EPA's list of WaterSense products.
  3. Water your lawn deeply but infrequently – the rule of thumb is one inch per week. Find a certified irrigation professional to install, maintain, or audit your home's irrigation system to ensure it's watering at peak efficiency. Switching to drought tolerant grasses or letting the lawn go dormant during the summer can also save significant amounts of water.
  4. Use techniques such as natural landscaping, rain gardens, rain barrels, green roofs and permeable paving that conserve water and allow rain to soak into the ground. See EPA's landscaping tips for ideas.
  5. Visit EPA's WaterSense for Kids with your child for more tips and activities about conserving water at home.

References

Below is a listing of references used in this report.

  1. British Columbia: Ministry of Forests, Lands and Natural Resource Operations. (2016). Adapting Natural Resource Management to Climate Change in the West and South Coast Regions: Considerations for Practitioners and Government Staff.
  2. Elsner, M.M., L. Cuo, N. Voisin, J. Deems, A.F. Hamlet, J.A. Vano, K.E.B. Mickelson, S.Y. Lee, and D.P. Lettenmaier. 2010. Implications of 21st century climate change for the hydrology of Washington State. Climatic Change 102(1-2): 225-260, doi: 10.1007/s10584-010-9855-0.
  3. Mauger, G.S., J.H. Casola, H.A. Morgan, R.L. Strauch, B. Jones, B. Curry, T.M. Busch Isaksen, L. Whitely Binder, M.B. Krosby, and A.K. Snover, 2015. State of Knowledge: Climate Change in Puget Sound. Report prepared for the Puget Sound Partnership and the National Oceanic and Atmospheric Administration. Climate Impacts Group, University of Washington, Seattle. doi:10.7915/CIG93777D
  4. Mote, P.W., A. Petersen, S. Reeder, H. Shipman, and L.C. Whitely Binder. 2008. Sea Level Rise in the Coastal Waters of Washington State. Report prepared by the Climate Impacts Group, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Oceans, University of Washington, Seattle, Washington and the Washington Department of Ecology, Lacey, Washington.
  5. Mote, P.W., and E.P. Salathé. 2010. Future climate in the Pacific Northwest. Climatic Change 102(1-2): 29-50, doi: 10.1007/s10584-010-9848-z.
  6. Snover, A.K., P.W. Mote, L.C. Whitely Binder, A.F. Hamlet, and N.J. Mantua. 2005. Uncertain Future: Climate Change and Its Effects on Puget Sound. Climate Impacts Group, Center for Science in the Earth System, Joint Institute for the Study of the Atmosphere and Oceans, University of Washington. http://cses.washington.edu/db/pdf/snoveretalpsat461.pdf.
  7. White, T., Wolf, J., Anslow, F., Werner., and Creative, R. 2002, updated 2016. Indicators of Climate Change for British Columbia (PDF). British Columbia Ministry of Environment.
  8. Allen, D. M.; Whitfield, P. H.; Werner, A. (2010): Groundwater level responses in temperate mountainous terrain: Regime classification, and linkages to climate and streamflow. In Hydrological Processes 24 (23), pp. 3392–3412.
  9. Environment Canada. 2004. Threats to Water Availability in Canada. National Water Research Institute, Burlington, Ontario. NWRI Scientific Assessment Report Series No. 3 and ACSD Science Assessment Series No. 1. 128 p. http://publications.gc.ca/site/eng/327331/publication.html.
  10. Fleming, Sean W.; Whitfield, Paul H.; Moore, R. D.; Quilty, Edward J. (2007): Regime-dependent streamflow sensitivities to Pacific climate modes cross the Georgia–Puget transboundary ecoregion. In Hydrological Processes. 21 (24), pp. 3264–3287.
  11. Fisheries and Oceans Canada. 1997. Wild, Threatened, Endangered and Lost Streams of the Lower Fraser Valley- Summary Report. Lower Fraser Valley Stream Review, Volume 3. ISBN 0-662-26029-5. Catalogue number FS23-304/8-1997E.
  12. Fisheries and Oceans Canada. 1999. Lower Fraser Valley Streams Strategic Review. Lower Fraser Valley Stream Review, Volume 1. ISBN 0-662-26167-4. Catalogue number Fs23-323/1-1997E.
  13. Helsel, D.R. and R.M. Hirsch, 1991. Techniques of Water-Resources Investigations Book 4, Chapter A3. U.S. Geological Survey, Reston, VA. https://pubs.er.usgs.gov/publication/twri04A3.
  14. Lins, H. F. and J.R. Slack, 1999. Streamflow Trends in the United States. Geophysical Research Letters, Vol. 26, No. 2, Pages 227-230, January 15, 1999. American Geophysical Union.
  15. Shrestha, R. R.; Schnorbus, M. A.; Werner, A. T.; Berland, A. J. (2012): Modelling spatial and temporal variability of hydrologic impacts of climate change in the Fraser River basin, British Columbia, Canada. In Hydrological.Processes 26 (12), pp. 1841–1861.
  16. Wang, J. Y.; Whitfield, P.H.; Cannon, A. J. (2006): Influence of Pacific Climate Patterns on Low-Flows in British Columbia and Yukon, Canada. In Canadian Water Resources Journal 31(1), pp 25-40.
  17. Whitfield, P. H.; Reynolds, C. J.; Cannon, A. J. (2002): Modelling streamflow in present and future climates: Examples from the Georgia Basin, British Columbia. In Canadian Water Resources Journal 27 (4), pp. 427–456.
  18. Whitfield, P. H.; Wang, J. Y.; Cannon, A. J. (2003): Modelling Future Streamflow Extremes - Floods and Low Flows in Georgia Basin, British Columbia. In Canadian Water Resources Journal 28 (4), pp. 633–656.
  19. Environment and Climate Change Canada (2019). Historical Hydrometric Data. Retrieved August 2019 from https://wateroffice.ec.gc.ca/search/historical_e.html.
  20. Puget Sound Partnership (2019). Summer Low Flows. Retrieved August 2019 from https://vitalsigns.pugetsoundinfo.wa.gov/VitalSignIndicator/Detail/46.
  21. British Columbia: Ministry of Forests, Lands and Natural Resource Operations. (2016). Adapting Natural Resource Management to Climate Change in the West and South Coast Regions: Considerations for Practitioners and Government Staff.
  22. Elsner, M.M., L. Cuo, N. Voisin, J. Deems, A.F. Hamlet, J.A. Vano, K.E.B. Mickelson, S.Y. Lee, and D.P. Lettenmaier. 2010. Implications of 21st century climate change for the hydrology of Washington State. Climatic Change 102(1-2): 225-260, doi: 10.1007/s10584-010-9855-0.
  23. Hutchinson, P. (personal communication). 2020.
  24. Snover, A.K., C.L. Raymond, H.A. Roop, H. Morgan, 2019. No Time to Waste. The Intergovernmental Panel on Climate Change’s Special Report on Global Warming of 1.5°C and Implications for Washington State. Briefing paper prepared by the Climate Impacts Group, University of Washington, Seattle. Updated 02/2019.
  25. Murdock, T.Q., S.R. Sobie, H.D. Eckstrand, and E. Jackson, 2012, revised April 2016: Georgia Basin: Projected Climate Change, Extremes, and Historical Analysis, Pacific Climate Impacts Consortium, University of Victoria, Victoria, BC, 63 pp.
  26. CBC News. (2020, January 21). Drought-ravaged Koksilah River on Vancouver Island to get monitoring wells. CBC News with audio files from All Points West with Kathryn Marlow. Retrieved on September 23, 2020 from: https://www.cbc.ca/news/canada/british-columbia/koksilah-river-monitoring-wells-1.5434185.
  27. The Canadian Press (2009, November 20). Flood forces Vancouver Island evacuations. CBC News. Retrieved on September 23, 2020 from https://www.cbc.ca/news/canada/british-columbia/flood-forces-vancouver-island-evacuations-1.822259.
  28. Simpson, S. (2020, February 4). Cowichan’s state of emergency remains as flood damage reckoning begins. Cowichan Valley Citizen. Retrieved on September 23, 2020 from ttps://www.cowichanvalleycitizen.com/news/cowichans-state-of-emergency-remains-as-flood-damage-reckoning-begins/.
  29. CHEK News (2019, May 28). Volunteers race to save salmon in drying Cowichan River. CHEK News. Retrieved on September 23, 2020 from https://www.cheknews.ca/volunteers-race-to-save-salmon-in-drying-cowichan-river-564108/.
  30. Barron, R. (2019, August 20). Province begins restricting water use on Koksilah River. Cowichan Valley Citizen. Retrieved on September 23, 2020 from https://www.cowichanvalleycitizen.com/news/province-begins-restricting-water-use-on-koksilah-river/.
  31. Barron, R. (2020, January 14). New wells will monitor Koksilah watershed after critical drought in 2019. Cowichan Valley Citizen. Retrieved on September 23, 2020 from https://www.cowichanvalleycitizen.com/news/new-wells-will-monitor-koksilah-watershed-after-critical-drought-in-2019/.

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