Taylor Creek AOP Report.pdf

Taylor Creek AOP December 7, 2020

Taylor Creek Aquatic Organism Passage Design Report

INTRODUCTION AND BACKGROUND

This report presents the geomorphic, hydrologic, hydraulic, and ecological considerations for a proposed Aquatic Organism Passage (AOP) structure at the Taylor Creek crossing on Yale-Kilgore Road. Taylor Creek is a perennial stream and bears fish.

Due to the existing undersized culvert, the crossing undergoes regular nuisance flooding during spring runoff periods. During flood events, water overtops the shallow banks near the inlet and is conveyed through a ditch to the cattle guard located approximately 500’ south of the crossing. When the cattle guard is inundated, flood waters overtop the road and flows south through swales, eventually merging back into Taylor Creek.

GEOMORPHIC CHANNEL DESCRIPTION

The Rosgen stream classification method used to evaluate the general geomorphic characteristics for this reach. In the vicinity of the Yale-Kilgore Road crossing, Taylor Creek most closely resembles a Rosgen C4 Stream. The average grade of the stream is 1.3% and the longitudinal profile is very uniform with no major grade breaks. The channel substrate is predominately comprised of large gravel and small cobbles with sands accounting for the finer particles (See attached pebble count for gradation). The bedforms observed consist primarily of riffle-run sequences with no presence of woody debris. The channel is moderately entrenched with a calculated entrenchment ratio of 2.1. In the designated Reference Reach, the channel cross section contains an approximate 6’ wide low-flow channel with approximately 8’ additional feet floodplain to give a bankfull width of 14’. The 8’ floodplain is inundated annually during spring runoff periods. The bankfull height is approximately 1.1’ and the adjacent alluvial valley is very flat and primarily vegetated with sage brush. It’s to be noted, that although the pipe is hydraulic undersized, there was no evidence of aggradation at the inlet or a plunge pool at the outlet which is typically observed with undersized crossings.

CHANNEL DATA

Rosgen Classification: C4 Bankfull Width = 14 ft Bankfull Depth = 1.1 ft Average Slope = 1.3% Substrate Gradation:

D16 = 13 mm D50 = 69 mm D84 = 181 mm

Average Key Piece Size = 300 mm Bedforms = Riffle-Runs comprised of gravel and cobbles Sinuosity = 1.15 Entrenchment Ratio = 2.4 Bankfull Width to Depth Ratio = 15.5

See appended Supporting File folder for Pebble Counts.

Photo 1: Taylor Creek at the designated upstream Reference Reach.

CHANNEL STABILITY

The stability of the channel was evaluated using both qualitative and quantitative analysis. The following data were collected prior to the evaluation: aerial photos, topographic maps, stream channel survey, hydrologic estimates, and anecdotal crossing history.

According to Rosgen’s research, type “C” streams are typically slightly entrenched with well-developed floodplains, relatively sinuous, and have a pool/riffle bedform morphology with characteristic point bars within the active channel. Rosgen indicates that the vertical and lateral stability (aggradation/degradation and lateral extension) of the type “C” stream is not only inherently dependent on the natural stability of the stream bank and upstream watershed conditions (that is, flow and sediment regime) but is also sensitive to changes in these conditions. The channel may be significantly altered and rapidly destabilized when changes in bank stability or watershed conditions are combined to cause an exceedance of the channel stability threshold.

Channel stability, vertical adjustment potential (maximum degradation), and proposed culvert profile design was determined through longitudinal stream profile analysis procedures established by the U.S. Forest Service. The USFS Longitudinal Profile Procedure can be found in the appended Supporting Files folder. See Appendix A - Longitudinal Profile for Taylor Creek.

The analysis uses the following processes to determine vertical adjustment potential and proposed culvert profile:

1. Draw segmented lines on the profile that span from the top of grade controls. The segments represent the average stream slope between grade breaks.

2. Measure the maximum pool depth for each section (distance from segmented lines to the bottom of pool)

3. Offset the segment by the maximum pool depth value multiplied by a safety factor of

1.75 corresponding to a riffle stream with gravel-cobble substrate (for factor of safety values, see page 20 of USFS Longitudinal Profile Procedure in the Supporting Files folder). The resulting offset segment line represents the potential for vertical adjustment.

The channel profile is very uniform with no major grade breaks observed. The lack of knickpoints suggests that the channel is relatively stable in the vicinity of the crossing.

HYDROLOGIC & HYDRAULIC CONSIDERATIONS

USGS StreamStats was used to estimate the flood magnitude for the 2- and 100-year events at the crossing (see Appendix C – StreamStats Report). The results for the 7.22 square-mile tributary area were:

Q2 = 138 CFS

Q100 = 407 CFS

The StreamStats estimate assumes all runoff generated from the delineated drainage area concentrates at the road crossing. It can be observed from the aerial of the upstream reach (see Appendix D – Upstream Swale Map Exhibit), that diverging floodplain swales intercept flow in large floods. These floodplain swales cross the road at differing locations than the Taylor Creek AOP point of interest. Therefore, it can be assumed that the StreamStats hydrologic is too conservative since the point of interest only bears a portion of the flood flows generated from the upstream drainage area.

Using FHWA hydraulic modeling program, HY-8, a capacity analysis was performed for proposed structure for the Q100 event (407 CFS). The resulting headwater to depth ratio (HW/D) was found to be 1.07. This exceeds the recommended 0.8 HW/D capacity recommended by the USFS.

However, it is our opinion that the HW/D exceedance presents minimal risk to the structure and road crossing for the following reasons:

1. As mentioned before, upstream flood plains swales intercept a portion of the flood flows.

This suggests that the 407 CFS Q100 value estimated by Stream Stats and used in the analysis is too high. The structure will have capacity to covey flood events of lesser magnitude without surcharge.

2. From field observations and anecdotal information from Clark County road maintenance personnel, it is evident that flood waters breach the channel banks upstream of the culvert. The upland area is relatively flat and likely provides flood storage during large events. The Stream Stats hydrology analysis does NOT factor in upland flood storage – which makes the 407 CFS Q100 value a conservative estimate for a single point crossing.

3. The upland area consists of open sage brush habitat. There is very little potentially for large woody debris in the design reach. Therefore, the freeboard redundancy implied by the 0.8 HW/D requirement will likely not be utilized nor necessary.

STRUCTURE SELECTION

The proposed structure for the crossing is a Three-Sided Concrete Box Culvert with an 18’ span.

The three-sided concrete box is necessary for this site for its low clearance properties. The stream alignment parallels the road just upstream of the crossing. Raising road grade in this area would put the proposed fill slope in conflict with the stream.

An open-bottom structural plate arch is feasible but would require a vertical wall just north of the crossing to prevent road slope from conflicting with the stream. A three-sided concrete box culvert in conjuncture with wingwalls would allow for a shorter structure length than an open-bottom structural plate arch.

A shorter structure length is ideal for the crossing due to the large skew of the stream alignment to the centerline of the road. The stream also has sharp bends near the inlet and outlet of the existing culvert. A shorter length would allow for a more natural hydraulic alignment and would put the proposed structure a further distance away from scour that naturally on the inside of stream bends.

Photo 2: Outlet of Culvert

Photo 4: Inlet of Culvert Photo 3: Stream reach located immediately upstream of bend at inlet

Appendix A: Longitudinal Profile

0+50 1+00 1+50 2+00 2+50 3+00 3+50 4+00 4+50 5+00 5+50 6+00

6,496 6,496

6,498 6,498

6,500 6,500

6,502 6,502

6,504 6,504

6,506 6,506

6,508 6,508

6,510 6,510

6,512 6,512

6,514 6,514

6,516 6,516

6,518 6,518

6,520 6,520

6,522 6,522

6,524 6,524

6,526 6,526

6,528 6,528

6,530 6,530

Proposed Design Grade

Adjustment Potential

Maximum Vertical

EL. 6510.37

Bottom of Proposed Footing along thalweg of the stream

Approximate Existing Ground

Existing Culvert

1.86%

LONGITUDINAL PROFILE

TAYLOR CREEK AOP

1.00%

1.12%

Precast Concrete Footing

0.00%

STATE PROJECT

NUMBER

SHEET

ID CLARK 6805(1) Profile 1

FREMONT 6805(1)

:3

A

M

A p r il

L o n g P r o f il e

S h e e t]

F

.0

W

F L

H D

Y a le

-K il g o re

R o a d

D e s ig n \D

G N

\i d -a

Y a le

-K il g o re

\i d -a

A

O P

.d g n

Appendix B: Surveyed Stream Cross Sections

UPSTREAM CROSS SECTION - STA 1+27.94

0+10 0+60

DOWNSTREAM CROSS SECTION - STA 6+86.10

0+40 0+90

6505 6505

6515 6515

TAYLOR CREEK

STREAM CROSS SECTIONS

MARCH, 2020&

ENGINEERS

PLANNERS

SURVEYORS

Appendix C: StreamStats Report

7/30/2019 StreamStats https://streamstats.usgs.gov/ss/ 1/3

18698 - StreamStats Report

Basin Characteristics

Parameter Code Parameter Description Value Unit

DRNAREA Area that drains to a point on a stream 7.22 square miles

PRECPRIS10 Basin average mean annual precipitation for 1981 to 2010 from PRISM

39.9 inches

Peak-Flow Statistics Parameters[Peak Flow Region 6 and 8 2016 5083]

Region ID: ID Workspace ID: ID20190730171535245000 Clicked Point (Latitude, Longitude): 44.47059, -111.65575 Time: 2019-07-30 11:15:54 -0600 https://streamstats.usgs.gov/ss/ 2/3

Parameter Code Parameter Name Value Units

Min Limit

Max Limit

Parameter Code Parameter Name Value Units

Min Limit

Max Limit

DRNAREA Drainage Area 7.22 square miles

2.77 3740

PRECPRIS10 Mean Annual Precip PRISM 1981

39.9 inches 18.9 54.6

Peak-Flow Statistics Flow Report[Peak Flow Region 6 and 8 2016 5083]

PIl: Prediction Interval-Lower, PIu: Prediction Interval-Upper, SEp: Standard Error of Prediction, SE:

Standard Error (other -- see report)

Statistic Value Unit PIl PIu SEp

1.25 Year Peak Flood 91.1 ft^3/s 32.2 257 66.9

1.5 Year Peak Flood 111 ft^3/s 41.1 302 63.7

2 Year Peak Flood 138 ft^3/s 52.6 361 61.3

2 33 Year Peak Flood 152 ft^3/s 57.8 397 61.1

5 Year Peak Flood 201 ft^3/s 76 532 61.7

10 Year Peak Flood 250 ft^3/s 91.9 679 63.8

25 Year Peak Flood 308 ft^3/s 107 887 68.1

50 Year Peak Flood 351 ft^3/s 117 1050 71.5

100 Year Peak Flood 407 ft^3/s 130 1280 75.1

200 Year Peak Flood 449 ft^3/s 137 1470 78.8

500 Year Peak Flood 525 ft^3/s 150 1830 84

Peak-Flow Statistics Citations

Wood, M.S., Fosness, R.L., Skinner, K.D., and Veilleux, A.G.,2016, Estimating peak-flow frequency statistics for selected gaged and ungaged sites in naturally flowing streams and rivers in Idaho: U.S. Geological Survey Scientific Investigations Report 2016–5083, 56 p.

(http://dx.doi.org/10.3133/sir20165083)

USGS Data Disclaimer: Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.

http://dx.doi.org/10.3133/sir20165083 https://streamstats.usgs.gov/ss/ 3/3

USGS Software Disclaimer: This software has been approved for release by the U.S. Geological Survey (USGS). Although the software has been subjected to rigorous review, the USGS reserves the right to update the software as needed pursuant to further analysis and review. No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. Furthermore, the software is released on condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from its authorized or unauthorized use.

USGS Product Names Disclaimer: Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Application Version: 4.3.8

Appendix D: Upstream Swale Map Exhibit

Taylor Creek: Main Channel Floodplain Swales

Floodplain Swale Diverging Point

Floodplain Swale - Road Crossing

Road Crossing

Appendix E: HY-8 Results – Capacity Analysis

HY-8 Culvert Analysis Report

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 407 cfs

Design Flow: 407 cfs

Maximum Flow: 407 cfs

Table 1 - Summary of Culvert Flows at Crossing: Taylor Creek Headwater Elevation

(ft) Total Discharge (cfs) Box Culvert

Discharge (cfs) Roadway Discharge

(cfs) Iterations

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6519.08 407.00 407.00 0.00 1

6522.10 640.49 640.49 0.00 Overtopping

Table 2 - Culvert Summary Table: Box Culvert Total

Discharge (cfs)

Culvert Discharge

(cfs)

Headwater Elevation (ft)

Inlet Control Depth (ft)

Outlet Control

Depth (ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwater Depth (ft)

Outlet Velocity

(ft/s)

Tailwater Velocity

(ft/s)

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

407.00 407.00 6519.08 4.281 4.997 7-M1t 3.611 2.799 3.909 3.909 6.240 6.545

Straight Culvert

Inlet Elevation (invert): 6514.08 ft, Outlet Elevation (invert): 6513.24 ft

Culvert Length: 45.01 ft, Culvert Slope: 0.0187

Culvert Data Summary - Box Culvert

Barrel Shape: User Defined

Barrel Span: 18.00 ft

Barrel Rise: 4.67 ft

Barrel Material: Corrugated Metal Riveted or Welded

Embedment: 0.00 in

Barrel Manning's n: 0.0350 (top and sides)

Manning's n: 0.0600 (bottom)

Culvert Type: Straight

Inlet Configuration: Thin Edge Projecting

Inlet Depression: None

Site Data - Box Culvert

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 ft

Inlet Elevation: 6514.08 ft

Outlet Station: 45.00 ft

Outlet Elevation: 6513.24 ft

Number of Barrels: 1

Water Surface Profile Plot for Culvert: Box Culvert

Crossing Front View (Roadway Profile): Taylor Creek