Identification of King County Streams with Declining Summer

Flows

Curtis DeGasperi, curtis.degasperi@kingcounty.gov

King County Water and Land Resources Division

July 13, 2010

HydroFutures: Water Science, Technology, and Communities

Motivation

• Wastewater Treatment Division Reclaimed Water Comprehensive Planning Process– What are the potential volumes

of reclaimed water that would be needed to serve the potential uses for reclaimed water?

http://www.kingcounty.gov/environment/wastewater/ReclaimedWater/CompPlan.aspx

Human Impacts on Water Cycle• Land cover change

– Forest clearing/Development

~1880

~1880

“Trends in Qmean and Qmin were not consistent in urban streams and, in fact, trends in these statistics were observed for some suburban and rural streams lacking extensive changes in land use atthe scale of a drainage basin over the entire period of record. Although urban development may affect Qmean or Qmin in some streams, relations between development and these statistics were not consistent.” p. 35

- Konrad and Booth (2002)

Human Impacts on Water Cycle

Water management– Surface water and groundwater extraction– Consumptive uses (Irrigation)– Septic vs Wastewater conveyance– Pipeline infiltration/exfiltration

Water Management

Basin Water Resources Streamflow

Water Supply System

Wastewater Disposal

Withdrawals

ExportsImports

Exports

Return via septic system disposal

Precipitation

I & I

Evaporation/Transpiration

Weight-of-Evidence Approach

• Review previous studies and reports

• Evaluate long term stream flow data for trends

Previous Studies/Reports

Selected Stream Gauges

General Approach

• Conduct trend analysis on mean annual and summer (7-day) low flow

• Include consideration of trends in precipitation and temperature (Sea-Tac)

• Attempt to provide some explanation for observed trends

King County. 2009. Working Draft. Identification of Streams Likely to Benefit from Additional Water Inputs. Prepared by Curtis DeGasperi and Jeff Burkey. Water and Land Resources Division, Seattle, WA.

Trend Analysis• Non-parametric “distribution free” method

– Mann-Kendall Trend test

http://pubs.usgs.gov/sir/2005/5275/

Trend Analysis

• p between 1.0 and 0.1 (weakest evidence)

• p between 0.1 and 0.05 (weak evidence)

• p between 0.05 and 0.01 (strong evidence)

• p <0.01 (strongest evidence)

“Nothing is certain, but I think some things are more nearly

certain than others”- Bertrand Russell (paraphrased)

Trend AnalysisCreek basin 7-Day Low Flow Mean Annual Flow p-value TRENDBear Creek ↓ ↑ <0.01 Very Strong EvidenceBig Soos Creek ↓ ↓ 0.01-0.05 Strong Evidence INCREASINGCanyon Creek ↑ ↓ 0.05-0.10 Weak EvidenceCovington Creek ↑ ↓ >0.10 Weakest EvidenceDes Moines Creek ↓ ↑ 0.05-0.10 Weak EvidenceDes Moines Creek ↓ ↑ 0.01-0.05 Strong Evidence DECREASINGEvans Creek ↓ ↑ <0.01 Very Strong EvidenceIssaquah Creek near Hobart ↑ ↑Issaquah Creek near mouth ↓ ↓Issaquah Creek, North Fork ↓ ↓Jenkins Creek ↑ ↓Laughing Jacobs Creek ↑ ↑May Creek at mouth ↓ ↓May Creek at Coal Creek Pkwy ↓ ↑Mercer (Kelsey) Creek ↑ ↑Miller Creek Detention Fac. ↓ ↓Miller Creek near mouth ↑ ↑Newaukum Creek ↓ ↓Patterson Creek ↓ ↑Raging River ↓ ↓Sammamish River ↓ ↓Taylor Creek ↓ ↑

Trends in Summer Low Flow

Big Soos Creek (example)

Precipitation Trends

Newaukum Creek (example)

Air Temperature Trends

Potential influence on ET

• Model with temperature trend

• Model without temperature trend

?

Sea-Tac (Jensen-Haise)

0

5

10

15

20

25

1940 1960 1980 2000 2020

Po

ten

tia

l E

T (

inc

he

s)

Big Soos Creek (example)

Water Conservation

Additional Explanation?

• To what extent can the effect of land cover change and water management activities be ascribed to these changes?

King County. 2009. Working Draft. Preliminary Estimates of Summer Environmental Restoration Flow Targets in Streams Identified as Likely to Benefit from Additional Water Inputs. Prepared by Curtis DeGasperi. Water and Land Resources Division, Seattle, WA.

Land Cover Effect

• HSPF model unit flow predictions by Hydrologic Response Unit– Forested Till– Disturbed Till– Forested Outwash– Disturbed Outwash– Saturated Soils– Effective Impervious Area

Water Management

Basin Water Resources Streamflow

Water Supply System

Wastewater Disposal

Withdrawals

ExportsImports

Exports

Return via septic system disposal

Precipitation

I & I

Evaporation/Transpiration

Water Management

• Sammamish-Washington Basin – King County (2001)

• Green River Basin– Northwest hydraulic consultants (2005)

King County. 2001. Screening level analysis of 3rd order and higher WRIA 8 streams for change in hydrologic regime. Draft report prepared by David Hartley for the WRIA 8 Technical Subcommittee on Flow Regime. King County Department of Natural Resources, Water and Land Resources Division: Seattle, WA.

Northwest Hydraulic Consultants, Inc. 2005. Assessment of current water quantity conditions in the Green River basin. Prepared for WRIA 9 Steering Committee. Northwest Hydraulic Consultants, Inc., Seattle, WA.

Human Influence

Big Soos Creek (12112600)

July – October 2007

ManagementWaterofEffectChangeCoverLandofEffect

FlowBaseCurrentFlowBaseSummerNatural

QQ

QQ

FlowBaseCurrentFlowBaseSummerNaturalFlowstorationtalEnvironmen QQQ Re

Human Influence

• Environmental Flow Targets (cfs)

- 0.9 to 5 cfs

- 5 to 10 cfs

-10 to 25 cfs

Human Influence

• Reduction in natural flow (%)

- 14 to 37 %

- 38 to 59 %

- 60 to 82 %

Human Influence

• Relative importance of land cover vs water management?– Depends on basin

• Highly urbanized basin with external water sources• Suburban basin with local water sources• Modified by type of wastewater disposal system

and/or irrigation practices

Evidence for Potential Human Influence?

Mercer/Kelsey Creek in Bellevue, WA

Evidence for Potential Human Influence?

Bellevue, WA

Conclusions

• Well designed long-term gauging network

• Compilation and access to up-to-date water management data

• Good models to synthesize information and extrapolate to ungauged basins

“No amount of sophistication is going to allay the fact that all your knowledge is about the past and all your decisions are about the

future”- Ian E. Wilson (former chairman of GE)