Limitation to qualitative stability indicators. the real world is a continuum, not a dichotomy ~ 100 % 30 % ~ 100 % ~ 40 %

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1 Stream Stability Assessment & BEHI Surveys Joe Rathbun MDEQ Water Resources Division Stability Stream can transport its water and sediment inputs without changing channel dimensions Width, depth, slope Complicating Issues Local Causes Easy to Identify Stream bank & bed mobility is natural Unnatural bank & bed mobility can have multiple causes Causes can be local or largerlarger-scaled Local causes can be fixed with local best management practices (BMPs) Large--scale causes can only be fixed Large with largelarge-scale BMPs 1

2 Large--Scale Causes Harder to Large Identify Most common cause of large--scale channel large degradation = Hydrologic alteration and increasing sediment loads due to landuse changes Causes of Hydrologic Alteration Impervious surface Soil compaction Vegetation change Dams Tile drainage Water withdrawal Sources of Increased Sediment Loads Upland erosion Agriculture, forestry, general development Stream bank erosion 10 to 90 % of total sediment load Results of Hydrologic Alteration Changes in: Peak flows Stream flashiness Channel dimensions Width Depth Sinuosity Slope Results of Increased Sediment Loads Loss of macroinvertebrate & fish habitat Buried riffles Loss of pools Channel filling (aggradation (aggradation)) = channel widening Dam failures 2

3 Indicators of Channel Condition Positive Qualitative Indicators: Herbaceous Vegetation Qualitative Observational Quantitative Observational = Bank Erosion Hazard Index (BEHI) Measurement Measurement--based = several options Positive Qualitative Indicators: Aquatic Moss Unvegetated MidMid-Channel Bar, or Braided Channel Positive Qualitative Indicators: Sensitive Fish or Mussels Leaning Trees on Both Sides 3

4 Exposed Infrastructure Failed BMPs Headcuts (= Nickpoints) Exposed Tree Roots on Both Sides Slumping Stream Banks Downstream of a Dam 4

5 Limitation to qualitative stability indicators Stable Unstable the real world is a continuum, not a dichotomy Bank Erosion Hazard Index BEHI developed by Dr. Dave Rosgen Seven metrics: Plant root depth Root density Bank angle Surface protection Bank composition Bank stratification (Bank Ht./Bankfull Ht.) BEHI Applicability Also not alluvial Alluvial channels only those that form themselves through sediment transport Alluvial Not alluvial Root Depth = depth relative to bank height, in % ~ 100 % 30 % Root Density = % of bank surface covered by roots ~ 100 % ~ 40 % Values: < 5; 5-14; 15-29; 30-49; 50-89; Scores: Values: < 5; 5-14; 15-29; 30-49; 50-89; Scores:

6 Surface Protection = % of bank covered by rocks, logs, etc. Bank Angle ~ to 90 Top of bank ~ 30% Values < 10; 10-14; 15-29; 30-49; 50-89; Values: 0-20; 21-60; 61-80; 81-90; ; > 119 Scores: 1.5 Bank angle hardest to get right? Adjustment Factors: Bank materials Bedrock, boulders, & cobble = decreased erosion risk Gravel & sand = increased erosion risk Bedrock = always Very Low Boulders = always Low Cobble = subtract 10 points Gravel or mostly gravel = add 5 points Sand or mostly sand = add 10 points Silt or clay = no adjustment Adjustment Factors: Bank stratification Sand layers within a bank of other materials = increased erosion risk No layers = no adjustment Single layer of erodible material = add 5 points Multiple layers of erodible materials = add 10 points Rural Stream Plant root depth 100 % Root density 90 % Bank angle 30º Surface protection = 90 % Materials = silt/loam BEHI = 9.5 = Low 6

7 Unstable Ag Stream Plant root depth < 5 % Urban Stream Root density < 5 % Plant root depth 40 % Bank angle 90º Root density 10 % Bank angle 85º Surface protection < 10 % Surface protection 10 % Materials = silt/loam Materials = sand = +10 (Upper Iowa River, MN) BEHI = 39 = Very High BEHI = 37 = Extreme Stable Ag Drain Unstable Ag Drain Plant root depth 100 % Plant root depth 10 % Root density 100 % Root density 15 % Bank angle 60º Bank angle 80º Surface protection 100 % Surface protection 5 % Materials = silt/loam Materials = sand = +10 BEHI = 7.5 = Low BEHI = 40.5 = Extreme Stabilized Bank Plant root depth 10 % Root density 20 % Bank angle 80º Surface protection 30 % Materials = silt/loam BEHI = 27 = High Urban stream, in park Plant root depth 90 % Root density 60 % Bank angle 90º Surface protection 0 % Materials = silt/loam BEHI = 21.5 = High 7

8 BEHI Application Local Problem = Local BMP BEHI Application Widespread Problem = Large-scale BMPs Low Low Project site Moderate Project site Moderate Extreme Extreme BEHI Pros Quantitative, & a continuum Minimal training required Low level of effort; 1 day = multiple stations Cons Inter-person variation No estimate of erosion rate or sediment loadings On-going Study to Calibrate BEHI BEHI + bank pin or toe pin measurements Quantify bank erosion rates and calculate sediment loadings for different BEHI categories Army Corps, DEQ, DNR Throughout Great Lakes states Calibrating BEHI Toe Pins Calibrating BEHI Toe Pins Eleventh St /20/2010 7/13/2011 Feet Feet BEHI = 10 = Low 1.Square feet of soil lost x bank length = cubic feet of soil lost 2.Cubic feet x soil density = mass of soil lost 8

9 Another option: cross-channel channel transects Elevation (ft) Station (ft) Richards-Baker Stream Flashiness Index Flashy stream = frequent, rapid, short-term term changes in streamflow Due to impervious surfaces, tile drainage, etc. Stream Flashiness Index Calculate using USGS gage station data Discharge (m 3 /sec) High Flashiness Index Time Low Flashiness Index Index SOUTH BRANCH AU SABLE RIVER NEAR LUZERNE, MI Stable flashiness Index AU SABLE RIVER AT MIO, MI Decreasing flashiness Water Year Water Year 9

10 Flashiness Index Results 308 sites Index AU SABLE RIVER AT GRAYLING, MI Complex flashiness Water Year Thanks! Questions? 10