Stream Simulation: A Simple Example

Transcription

1 Stream Simulation: A Simple Example North Thompson Creek, CO Paul T. Anderson U.S.D.A. Forest Service Here s How We Started May USDA-Forest Service

2 Here s How We Finished Forest Service Aquatic Organism Passage Policy Protect and Restore the Physical, Biological and Chemical integrity of the Nations Waters (CWA) Primary Design Priority: Aquatic organism passage and ecological connectivity is the goal and the first design priority for crossing streams that provide habitat for aquatic life. Other Design Considerations: Minimizing the consequences of plugging and overtopping, including the ability to prevent stream diversion. Sufficient hydraulic capacity, including the requirement that headwater depth does not cause pressurized flow at the maximum flood. Maximize benefits while minimizing life cycle cost. May USDA-Forest Service

3 Basic Concepts Bankfull Flow: Bankfull flow describes the volume, width, depth and elevation: where the water begins to spill on the flood plain. The elevation of incipient flooding. It can also be thought of as the streams physical expression of it s natural size and power. Stream Simulation: Create a channel bed form, within a structure, as similar as possible to the natural channel in both structure and function. The simulated channel should present no more of and obstacle to aquatic life than the adjacent natural channel. Reference Reach: A natural stable channel section used as the design template for stream simulation. 100 Year Flood: A backward looking estimate with Very High Error. Does not account for Debris, Sediment, or Aquatic Passage. At Best is an relative indicator or risk. Structure Life Phase 1 Initial Assessment Phase 2 Phase 6 Maintenance & Monitoring Phase 5 Construction Stream simulation project phases Site Assessment Phase 3 Stream Simulation Design Phase 4 Final Design & Contract Preparation May USDA-Forest Service

4 Phase 1 - Initial Assessment Road Context System road, heavy oil/gas, timber, recreation use. Resource Values Brook trout, CO cutthroat trout, and others? Watershed-Scale Risk Factors Stable sandstone geology, basalt cap, beetle kill Site Risk Factors Debris, floodplain constriction, channel stability Initial Assessment (cont.) Suitability and Objectives Road to remain in place with similar dimensions Stream simulation is applicable and appropriate Accommodate some floodplain processes Be prepared for some headcut, expect debris May USDA-Forest Service

5 Phase 2 - Site Assessment Develop plan view sketch map Collect Site Data Site and road topography Longitudinal Profile Channel and floodplain cross sections Bed material descriptions Conduct preliminary geotechnical investigation Bedrock, groundwater, mass wasting, engineering props. Upstream Channel Accessible floodplain Aggraded inlet. Sediment wedge upstream May USDA-Forest Service

6 Downstream Channel Minor scour pool, no bedrock Less sinuous but floodplain present Preliminary Site Sketch Provides good notes for Winter design sessions. May USDA-Forest Service

7 Preliminary Site Sketch Zoomed In Topographic Survey Map + May USDA-Forest Service

8 Longitudinal Profile sediment wedge Phase 3 Stream Simulation Design Select project alignment and profile From selected reference reach determine Slope similar to project profile Channel shape Bed material gradation and grade controls Select structure width and minimum embedment depth Verify stability of new streambed inside structure Results: Structure size, shape, alignment. Bed material sizes and configuration of grade controls. May USDA-Forest Service

9 New Structure Alignment Headwalls considered to reduce length but were too costly Longitudinal Profile Design Gradient segment elevation change (ft) segment length (ft) Sediment Wedge gradient % gradient difference betw een successive segments maximum residual pool depth (ft) number of grade controls distance betw een grade controls (ft) A B C , 30.8, D , E F , 40.29, G H I , 21.4 J K L culvert Reference Reach May USDA-Forest Service

10 Reference Reach Close gradient match. Grade controls. Sediment size. Stream Simulation Design: Select Bed Material Gradations Stream simulation materials to give you similar stability permeability Complexity Pebble count gradation of streambed Is the same as an engineering gradation (% passing & sieve size) Construct grade controls with largest material Individual rocks or graded material May USDA-Forest Service

11 Bed Material Characterization particle size interval name size interval (mm) count or frequency percent frequency cumulative percent finer Project Name: North Thompson Creek medium boulders 512 to Sample ID: PC (Site 2 channel, ) 362 to Sample Date: 10/12/2006 small boulders 256 to Sampler Name: Weinhold, Grove 181 to Sample Location: Riffle b/t XS 3 and 4 large cobbles 128 to Sample Method: sampling frame on transects 90.5 to approximately 1 meter apart, small cobbles 64.0 to within active bed width to very coarse gravel 32.0 to percentile particle size (mm) 22.6 to d coarse gravel 16.0 to d to d50 45 medium gravel 8.0 to d to d5 13 fine gravel 4.0 to to % boulders 6.9 very fine gravel 2.0 to % cobbles 31.7 sand, silt, or clay < % gravels 60.0 Total count % sands,silts,clays 1.4 Sediment Design From Reference Reach Data May USDA-Forest Service

12 Key Pieces too XS3-XS4 (Segment D Reference Reach). Summary of 10 largest particles for the key pieces. particle number long axis (mm) intermediate axis (mm) short axis (mm) average cubic dimension (mm) long axis/inter mediate axis ratio particle shape; roundness blocky- to tabular-shaped; subangular tabular- to disc-shaped; subangular blocky- to tabular-shaped; subangular tabular- to disc-shaped; subangular tabular- to disc-shaped; subangular tabular- to disc-shaped; subangular tabular- to disc-shaped; subangular blocky- to tabular-shaped; subangular blocky- to tabular-shaped; subangular blocky- to tabular-shaped; subangular average d95 percentile (mm) d84 percentile (mm) d50 percentile (mm) d16 percentile (mm) average cubic dimension of d95 percentile average cubic dimension of d84 percentile average cubic dimension of d50 percentile average cubic dimension of d16 percentile Stream Simulation Design: Structure Selection Analyze various structure sizes and shapes that meet design width: Minimize channel and floodplain constriction Room for debris as beetle activity increases (HW/D <<1 during design flood) Meets minimum cover requirements Adequate embedment below expected scour line May USDA-Forest Service

13 Structure Selection From Reference Reach XSECT Final Road Surface Lower Vertical Adjustment Line Structure Selection Idealized (easy to build) XSECT Final Road Surface Lower Vertical Adjustment Line May USDA-Forest Service

14 Structure Selection Trial Structure Types Final Road Surface 12-4 x 4-5 Box w/ concrete footings Lower Vertical Adjustment Line Structure Selection Trial Structure Types Final Road Surface Countersunk 12 x 7-8 CMPA Lower Vertical Adjustment Line May USDA-Forest Service

15 Stream Simulation Design: Structure Selection Final choice: Choose 12 x 7-8 CMPA Economical shape, large opening, embedment depth No poured concrete, fast installation Check Bed Material Choice: Is mobility of particles in structure similar to natural channel? Are key pieces (grade controls, banks, etc.) stable in design flood? Phase 4 Final Design and Contract Preparation Produce drawings and specifications for: structure and foundation details, bed material roadway, erosion control, dewatering, bypass roads, stockpile sites. and everything else Determine quantities and estimate costs Develop Contract Documents Results: Contract solicitation package May USDA-Forest Service

16 Plan Site and Plan, Profile, Drawing Survey Stream Simulation Channel Details May USDA-Forest Service

17 Typical Sections Phase 5 - Construction Inspection and control Documentation Design changes (minimize) Results: The completed project May USDA-Forest Service

18 Pre-Construction Items We (USFS) usually remove critters prior to construction Inspecting the Work Schedule Road Closures (try to avoid bypass roads) Verify Construction Staking May USDA-Forest Service

19 Completed Project Completed Stream Crossing for Aquatic Organisms Completed Road Crossing for traffic Phase 6 - Post Construction Maintenance and Monitoring Maintenance is minimal some tweaking of bed structure Monitoring - intensive for this project Implementation built as designed? Effectiveness bed stability, shape, complexity May USDA-Forest Service

20 Our responsibility to the Nation is to be more than careful stewards of the land, we must be constant catalysts for positive change Gifford Pinchot How long is the door going to be closed? earch.php May USDA-Forest Service