Sediment Transport Analysis for Stream Restoration Design: The Good, the Bad, and the Ugly. Brett Jordan Phd, PE HydroGeo Designs LLC. Land and Water Services Inc.
THE GOOD
THE BAD
THE UGLY
THE GOOD
THE BAD
THE UGLY
THE GOOD
THE BAD
THE UGLY
WHAT DO WE DO????
LOCATION IN WATERSHED Stream equilibrium and graded rivers (Gilbert 1877, Davis 1902, Mackin 1948) Fluvial audit and sediment impact assessments ( Sear and Newson 1993, Biedenharn et.al 2000) Balance sediment supply and transport for channel design (Lane 1955, Shields et.al 2003) After Sear and Newson (1993)
SEDIMENT SUPPLY
CAPACITY INCIPIENT MOTION (SEDIMENT COMPETENCE) TRANSPORT EQUATIONS BY GRAIN SIZE (BEDLOAD, SUSPENDED LOAD, TOTAL LOAD) FIELD MEASUREMENTS STREAM POWER, BED SHEAR VS. SEDIMENT LOAD
SUPPLY VS. TRANSPORT LIMITED Supply Limited- The reach has transport capacity to move all the upstream sediment delivered to the site, erosion could be an issue. Nonerodible THRESHOLD CHANNELS Transport Limited- The sediment load exceeds the reach transport capacity, deposition may be an issue.
MODE OF TRANSPORT SUSPENDED LOAD VS BED LOAD
BED MATERIAL LOAD VS WASHLOAD Bed Material Load- Portion of sediment load derived in appreciable quantities from the streambed Wash Load- Portion of the suspended sediment load not found in significant quantities in the stream bed. <D10. Supply Limited Washload transport is independent of stream transport capacity
URBAN SYSTEMS- TIRE RIFFLES
IMPORTANCE OF DATA SOURCES USGS SITES PROJECT FIELD MEASUREMENTS GEOMORPHIC OBSERVATIONS (BAR DEPOSITS) BED MATERIAL (PAVEMENT, SUB- PAVEMENT SAMPLES, PEBBLE COUNT) LOOK UPSTREAM AND DOWNSTREAM OF PROJECT REACH!
TRIAGE APPROACH LEVEL 1- MINIMAL SEDIMENT ISSUES, SHORT REACH PROJECTS <300 LF (INCIPIENT MOTION, PERMISSIBLE VELOCITY, BEFORE AND AFTER HYDRAULICS) LEVEL 2 ALLUVIAL REACHES WITH SEDIMENT SUPPLY (EFFECTIVE DISCHARGE, FLOWSED/POWERSED, SEDIMENT BUDGET) LEVEL 3 LONGER REACHES, HIGH SEDIMENT SUPPLY, HIGHER PROFILE AREAS WITH SEDIMENT ISSUES (SIAM, MULTIPLE FLOWSED/POWERSED RUNS, CONTINUOUS SIMULATION HEC 6, SRH 1-D, 2-D)
Sediment study level Example scenarios 1 Low sediment supply in small urban watersheds Hardpan reaches without active incision Current stable reaches with habitat improvements proposed Bank stabilization projects Short reach projects (<300 ft) Procedures Existing and proposed hydraulic analysis Permissible velocity analysis Sediment competence calculations 2 Sand bed channels with significant sediment supply, Reach scale projects (>300 ft) Incising hardpan reaches Alluvial silt bed channels where washload transitions to bed material load Reaches where active sediment deposition is observed Effective discharge analysis (flow duration analysis) FLOWSED/POWERSED analysis 3 Large scale channel projects with significant sediment supply High profile areas where long-term sediment deposition is a major concern Tidal areas where long-term sedimentation is a concern Multiple Runs of FLOWSED/POWERSED Analysis SIAM (HEC-RAS) analysis Mobile (1-D) bed continuous simulation models (HEC-6, SRH 1-D)
LEVEL ONE SCENARIO SMALL SCALE PROJECTS LIMITED SEDIMENT SUPPLY/TRANSPORT SUPPLY LIMITED CONDITIONS BANK STABILIZATION METHODS INCIPIENT MOTION/SEDIMENT COMPETENCE PERMISSIBLE SHEAR STRESS, VELOCITY BEFORE/AFTER HYDRAULICS
LEVEL TWO SCENARIO ALLUVIAL SEDIMENT TRANSFER REACH COULD BE TRANSPORT OR SUPPLY LIMITED BEDLOAD/BED MATERIAL LOAD SEDIMENT SUPPLY METHODS EFFECTIVE DISCHARGE FLOWSED/POWERSED SEDIMENT BUDGET TRANSPORT EQUATION APPROACH
fflowsed/powersed Stream Power Based Flow Duration Utilizes Field Collected Sediment Transport Data On line Database of Flow Records
LEVEL THREE SCENARIO LARGER SCALE PROJECTS >2000 LF SIGNIFICANT SEDIMENT SUPPLY/TRANSPORT THAT CAN IMPACT PROJECT SUCCESS HIGH PROFILE/HIGHER BUDGET PROJECTS TIDAL REACHES/DEPOSITIONAL REACHES WATERSHED SCALE STUDIES METHODS SIAM (SEDIMENT IMPACT ASSESSMENT METHODS) HECRAS MULTIPLE FLOWSED/POWERSED RUNS CONTINUOUS SIMULATION MOBILE BED MODELS (HEC 6, SRH- 1d, 2D) WARSSS
SIAM-Sediment Impact Assessment Model Sediment continuity by grain size based on channel hydraulics, annual flow duration curve, local sediment sources Transport takes place as wash load or bed material load Local sediment sources, upstream channel sources and reach transport capacity indicate aggradation or degradation in the modeled sediment reach - Local Balance
Local Balance Upstream bed material sediment supply IN Local sediment sources of bed material size Sediment Reach Reach transport capacity * fraction bed material present OUT
SIAM-Sediment Accounting Algorithm Upstream Wash Supply Wash Material Local Source Supply Upstream Transtioning Wash Material Upstream Channel Supply Channel Material Local Balance Local Channel Supply
SRH-1D (USBR) Continuous simulation model Steady flow discretization of hydrograph Exner sediment routing Layered bed material (pavement/subpavement)
SRH-1D Layered Bed Material Bulk Sampling (Pavement) Pebble count (Sub-pavement) (Bunte and Abt 2001) (Pavement) (Sub-pavement)
TAKE HOME POINTS UNDERSTAND THE SYSTEM AND SCALE OF YOUR PROJECT LOCATION IN THE WATERSHED QUANTIFY SEDIMENT SUPPLY AND CALIBER (IN SOME WAY) MODE OF TRANSPORT SELECT A LEVEL OF SEDIMENT ANALYSIS DETAIL APPROPRIATE FOR YOUR SCENARIO UNDERSTAND UNCERTAINTY
ALL MODELS ARE WRONG, BUT SOME ARE USEFUL George Box