NY FLAP DOT 63(1)_Hydra_Culvert_Memo.pdf

FHWA: tbenabdi Ph # (x6232):BM date: 9/12/2019 M:\PROJECTS\_ACCESS\NY\Projects\NY 04_NY FLAP DOT 63(1)\Techserv\Hydra\Reports\NY FLAP DOT 63(1)_Hydra_Culvert_Memo.docx CC: Hydraulics, Geotech, Env, HD Engineer, TS Engineer, Bridge

Form FHWA-201 U.S. DEPARTMENT OF TRANSPORTATION (Rev. 11-87) FEDERAL HIGHWAY ADMINISTRATION

MINUTE - MEMO

Use this form in lieu of transmittal slips within Dept. of Trans. when message comment is to be retained as file material. Do not prepare carbons. Not to be used in lieu of Form FHWA-121 for informal correspondence.

SUBJECT: NY FLAP DOT 63(1) - Preliminary Hydraulics Memo

TO MESSAGE/COMMENT FROM/DATE

Dan Weston Project Manager

Chris Burnell Highway Design Manager

We have completed the hydrologic and hydraulic analysis for the above-mentioned project based on available information. The project involved a reinforced concrete box (RCB) culvert design on S. Gravel Road (Route 63) within the Iroqois National Wildlife Refuge, Genessee County, New York (lat/lon: 43.125267°, -78.390484°). The project also includes two (2) culvert crossings located at lat/lon: 43.144235°, -78.390338° and 43.149683°, -78.390342°, respectively, that each convey runoff from east to west (and vice versa) via 3-36” diameter corrugated metal pipes (CMPs).

Route 63 is considered a high-standard roadway at this section, because it carries 6,000 vehicles per day. Thus, hydraulic design is required to meet the 50-year design storm per Chapter 7 of the PDDM. However, the hydrologic conditions of all crossings are flat, wetland areas, with interconnectivity. The roadway prism of Route 63 represents one of the high points in the watershed and the openings under the roadway provide equalization of hydrostatic pressures from one side to another. It is difficult to determine the design peak flows of each site with limited terrain data from each of the subsheds. Furthermore, the two sites with 36” diameter culverts are both outfalls for a stormwater management structure upstream of which the capacity and outfall performance data are not available. Thus, the three (3) sites are proposed for hydraulic equivalent replacements using assumed design flows and standard-sized crossings supported by analysis using the HY-8 computer program. See below narratives and tables of results for crossing analyzed.

Culvert (C410048:)

According to the draft scoping report, this is an existing 26’ length, 15’ span by 4.6’ high RCB crossing that has structural deficiencies and needs replacement. The existing culvert provides conveyance of 485cfs at a headwater elevation of 616.77’, without overtopping Route 63 (El. 617.5’), has a 1.2 headwater to depth (HW/D) ratio and the water surface elevation (WSE) below the shoulder hinge point.

We recommend replacing the current culvert crossing (above) with a proposed 30’ long, 16’ span by 8’ rise RCB with a 3.5’ embedment depth to match the channel elevation. The proposed culvert provides conveyance of the same 485cfs flow rate with a WSE below the bottom of the base layer of the road, a HW/D ratio of about 1.173, and a headwater elevation of 616.53’. The proposed RCB will be outfitted with headwalls and wingwall end treatments on up and downstream ends. This culvert site is located entirely outside of the FEMA special floodplain hazard area limits and there does not appear to be any specific permitting requirements at this location.

Tahir Benabdi Hydraulics Engineer

THROUGH

Abhi Kapoor Hydraulics Team Leader

September 27, Culvert (C116868): According to the draft scoping report, this is an existing RCB of 8 ft. span by 3.5 ft. rise by 29 ft. long and 2 CMP extensions, on both the left and right sides, with a 3-ft.

diameter by 10.5 ft. length. However, the mapping survey file shows 3-36” diameter CMPs throughout and was modeled as such in the HY-8 hydraulic model. A design flow was assumed to be about 100cfs, has a headwater elevation of 615.91’, produces a HW/D ratio of 1.2 and is below the hinge point of the shoulder. This crossing has been noted to have structural deficiencies and needs replacement per this project.

We recommend replacing the current CMP crossing (above) with a proposed 50’ long, 8’ span by 6’ rise RCB with a 3.0’ embedment depth to match the channel elevation. The proposed culvert provides conveyance of the same 100cfs flow rate with a WSE below the bottom of the base layer of the road, a HW/D ratio of 1.0, and a headwater elevation equal to existing conditions. The proposed culvert will be outfitted with headwalls and wingwall end treatments on up and downstream ends. This culvert site is located entirely outside of the FEMA special floodplain hazard area limits and there does not appear to be any specific permitting requirements at this location.

Design velocities show low increases from existing to proposed conditions; however, erosion control matting or stone will not be proposed, because the culvert will be embedded a depth of 3’ and the tailwater conditions are considered flat, wetland areas. Thus, the reasoning to provide outlet control and stabilization is not adequately justified for this crossing.

Culvert (C116888): According to the draft scoping report, this is an existing RCB of 10 ft. span by 2.5 ft. rise by 28’ long and 3 CMP extensions on both the up and downstream ends with a 3-

ft. diameter CMPs by 11 ft. length and a 3-ft. depth of cover. However, the mapping survey file shows 3-36” diameter CMPs throughout and was modeled as such in the HY-8 hydraulic model.

A design flow was assumed to be about 100cfs, has a headwater elevation of 618.10’, produces a HW/D ratio of 1.2 and is below the hinge point of the shoulder. This crossing has been noted to have structural deficiencies and needs replacement per this project.

We recommend replacing the current culvert crossing (above) with a proposed 48’ long, 8’ span by 6’ rise RCB with a 3.0’ embedment depth to match the channel elevation. The proposed culvert provides conveyance of the same 100cfs flow rate with a WSE below the bottom of the base layer of the road, a HW/D ratio of 1.0, and a headwater elevation equal to existing conditions. The proposed culvert will be outfitted with headwalls and wingwall end treatments on up and downstream ends. This culvert site is located entirely outside of the FEMA special floodplain hazard area limits and there does not appear to be any specific permitting requirements at this location.

Design velocities show low increases from existing to proposed conditions; however, erosion control matting or stone will not be proposed, because the culvert will be embedded a depth of 3’ and the tailwater conditions are considered flat, wetland areas. Thus, the reasoning to provide outlet control and stabilization is not adequately justified for this crossing.

Table 1. Existing Culvert Sizes Station Size Material Conveyance

Area (sf) Road El. (ft)

Inlet El.

(ft)

Outlet El. (ft)

Length (ft)

C410048 15’ span(s) x 4.6’ rise(r)

RCB 69 617.5 611.25 611.20 28.7

C116868 3-36” dia. CMP 21.195 617.9 612.16 612.14 612.46

612.20 609.53 612.76

52.20 (1*)

51.44 (2)

51.40 (3*)

C116888 3-36” dia. CMP 21.195 620.2 614.69 614.51 614.59

614.19 614.48 614.36

47.67 (1)

48.12 (2)

47.30 (3)

Asterisk (*) denotes negative slope in pipe per field survey.

Table 2. Proposed Culvert Sizes Station Size Material Conveyance

Area (sf) Road

El.

(ft)

Inlet El.

(ft)

Outlet El.

(ft)

Length (ft)

C410048 16’ s x 8’ r

RCB 72 (above 42” embedment)

617.5 611.25 611.20 30.0

C116868 8’ s x 6’ r

RCB 24 (above 36” embedment)

617.9 609.30 609.20 50.0

C116888 8’ s x 6’r

RCB 24 (above 36” embedment)

620.2 611.50 611.40 48.0

Table 3. Culvert Performance Storm Event

Assumed Culvert Design

Discharge (cfs)

Existing

WSE U/S

(ft)

Proposed

WSE U/S

(ft)

Existing Velocity

(fps)*

Proposed Velocity

(fps)*

Existing

HW/D

Proposed

HW/D

C410048 485 616.77 616.53 10.14 9.94 1.2 1.173 C116868 100 615.91 615.31 7.19 7.42 1.2 1.0 C116888 100 618.10 617.50 7.19 7.42 1.2 1.0

(*) Assumed TW depth of 0’ used in HY-8 to evaluate culvert performance.

If you should have any questions or concerns with the above recommendations, please feel free to contact us.