Poplar River Sediment Source Assessment

John L. NieberBruce N. Wilson

Department of Bioproducts and Biosystems Engineering

University of Minnesota

July 17, 2009

Timeline Impaired for turbidity on Minnesota’s

list of impaired waters (2004)MPCA must complete a study to

determine the total maximum daily load (TMDL)

TMDL study was started in 2006, but was not finished at the planned date (2008)

The MPCA requested that the U of M team continue the work and to estimate contributions of erosion sources

Targeted completion of the Draft TMDL is 2011

BackgroundHigh turbidity threatening

trout stream and health of Lake Superior

Turbidity is caused by suspended silt/clay

Poplar River is considered a nonpoint source (both natural and anthropogenic sources of pollution)

Significant streambank and bluff erosion observed; suspected as primary sources

Some measures have been taken to reduce the sediment load in the river (Mega Slump), and revegetation of bare surfaces

Specific Water Quality Problems

When comparing upstream to river mouth loading rates: Phosphorus increased by 2X Total suspended solids (TSS) by

6X Mercury levels exceeded the

state standard Mercury and TSS levels were

strongly correlated Reducing sediment loss rates

in the lower Poplar River will be beneficial for reduction of total mercury quantities into Lake Superior.

“…juvenile [trout] population has declined in the Poplar since 1989.”

Water quality sampling was conducted according to approved MPCA quality assurance procedures (MPCA, 2000)

Comparison of Turbidity at different sites in the

Poplar River

Comparison of Turbidity at different sites in the

Poplar River

Upstream (left) and downstream sites on the Poplar River, July 30, 2001 after a large rainfall (locations are approximately 3 mi apart)

Photo credits: MPCA 2002

114 square miles of drainage area

Lots of upland lakes and wetlands

Soils: red lake clay and Superior lobe till

25.5 miles of river Has the highest

percentage of urban land use of the monitored north shore trout streams (3.5%, mostly in the lower river area)

Stream bed is composed mostly of boulders and cobbles

Objectives (overall)Acquire archived data and assess data gaps;

acquire additional geomorphic data of the river and watershed, and other watershed data

Apply sediment generation and sediment transport models to assess potential sediment sources and their impact on loading and transport within the river

Evaluate and assess the sources of sediment entering and being transported within the Poplar River to Lake Superior

Current Activity (now until 10/30/09)

Acquiring and processing archived channel morphology data for critical sections of the lower Poplar RiverCollected by the Cook County SWCD, MPCA,

and MNDNRData gaps will be assessed and then filled in

within scope of the projectIdentify a reference watershed and stream to

compare sediment generationModeling work plans for future studies will be

formulated

WEPP model (LER, 2005 as listed in 9/2007 report by RTI)

An evaluation of soil type, land use type, and slope was conducted using a geographic information system.

The areas of distinct combinations of soil type, land use type, and slope were calculated for the Poplar River gorge area.

The land use type, soil type, and slope combination were simulated using WEPP.

Ski trails (tall and short grass); bare soils, forest, natural openings, and golf courses were simulated using the WEPP: Hillslope model.

Roads (Lutsen and non-Lutsen) were simulated using WEPP: Roads.

This average of 180 tons/year was compared by RTI (9/2007) to the sediment transported in 2002 which was 1,112 tons/year

WEPP model (LER, 2005 as listed in 9/2007 report by RTI)

WEPP model (LER, 2005 as listed in 9/2007 report by RTI,

9/2007)

WEPP model application by RTI (February 2008)

Estimate erosion from major land uses in lower Poplar River watershed

Used refined resolution of landscape features

Compared results to measured sediment loads

Quantified temporal distribution of loadsConducted sensitivity analysis

WEPP model application by RTI (February 2008)

Limitations of WEPP 2006.5 (watershed version)

Poor simulation of impervious areas Overestimate of erosion and sediment yield

may occur at larger watershed sizesDoes not include bank erosion or sloughing Does not include roads in the watershed version Does not include erosion from perennial

streams Does not simulate gully erosion

WEPP model application by RTI (February 2008)

Results

Average upland source of sediment estimated to be 76% of total load – compared to 20% in LER study

Trends between predicted and observed sediment load similar

Prediction shows that development has significant effect on sediment load

WEPP model application by RTI (February 2008)

WEPP model application by RTI (February 2008)

Expected data needs to fill gapsStream morphology

X-sectionsTexture of bank materialsBank Erosion Hazard Index (BEHI) of banksShear strength of bank materials

Landscape topography – LIDAR, field surveying

Identification of gullies and other concentrated sediment sources

Locations of road and trailsSoil characterization for runoff generation

Future ActivityWatershed modeling will be done to:

Better delineate the upland runoff erosion sources Determine contribution of different sources to

sediment loadField data will be used in three models to provide

estimates of erosion generated from the streambanks and bluffs – CONCEPTS, BSTEM, BEHI

Development of a method to monitor BMP effectivenessTest this method on the Mega Slump

U of M will assist the Cook County SWCD with incorporating the results of these tasks into the TMDL report

Configuring natural flow pathways

Topographic contours

Flow paths in Wisconsin watershed – derived digitally

Configuring natural flow pathways

Flow paths in Oklahoma watershed – derived digitally

Identifying location for erosion/sediment transport potential

tan( )sA

Distribution of unit stream power (watershed in SE Minnesota); from Moore and Nieber (1989)

Unit stream power

Data needs for upland erosion distribution

Detailed topographic dataBedrock depth – soil thicknessSoil hydraulic propertiesErodibility of soilsField verification of connectivity of

sources to ephemeral, intermittent or perennial stream channels

Questions?

Referenceshttp://www.lakesuperiorstreams.orghttp://www.pca.state.mn.ushttp://www.epa.govPoplar River, MN (Cook County), 2006

Automated, in situ, Water Quality Data: Preliminary Analysis