CO FLAP PUW16(1) Nichols Road Final Drainage Design Memo_100.pdf

CFL | CO FLAP PUW16(1) Nichols Road Drainage Memo hdrinc.com 1670 Broadway Suite 3400 Denver, CO 80202-4824

(303) 764-1520

Memo Date: Tuesday, September 01, 2020

Project: CO FLAP PUW16(1) Nichols Road

To: FHWA Central Federal Lands Division

From: Colleen Koenig

Subject: Final Drainage Memo

Introduction The Nichols Road and Trail Improvement is located in the community of Pueblo West, north of Lake Pueblo in Pueblo County. The proposed improvements include approximately 1.6 miles of new multi-use trail, pedestrian and bicyclist activated crossing signals at two locations, new pedestrian/bicycle bridge over the railroad, construction of new turn lanes and improvement to existing turn lanes, rehabilitation of approximately 0.7 miles of Nichols Rd, signage throughout the project area, and minimal drainage improvements.

Site Information The intent of the project is to provide multimodal improvements to enhance access to Lake Pueblo State Park (LPSP) and to improve safety through the northern entrance for vehicles, pedestrians, and cyclists. The roadway portion project extends from north entrance of LPSP along Nichols Rd to McCulloch Blvd. The multi-modal trail will begin at the park entrance as well but will continue along the existing trail system at S Camino De Bravo, see site map in Appendix A.

Per FEMA Panel 08101CO466D, the site is located in FEMA Zone X, Area of Minimal Flood Hazard, and proposed improvements will not impact existing floodplains. See Appendix A for FIRM Panel.

The topography of the site is flat with slopes ranging from 0-2% for the majority of the site, with steeper slopes present at the railroad crossing. The surrounding area is sparsely vegetated with low brush and native grasses. Soils present on site are primarily Hydraulics Soils Group Class B Manvel Silt Loam. The soil has a moderate infiltration rate. See Appendix B for NRCS soils report.

General drainage patterns for the Pueblo West Community are runoff draining from north to south to be collected in small tributaries that ultimately feed into Lake Pueblo.

Hydrology Due to the minimal drainage being proposed a hydrologic analysis was not completed for the site. The increase in impervious area is limited to 2’ of roadway widening along both sides of

Nichols Rd and the new trail connection resulting in an approximate 12% increase in imperviousness.

The proposed design will not alter existing drainage patterns and current flow patterns will be perpetuated across the site.

Existing Drainage From the south end of the project at the entrance to LPSP to the bridge crossing over the railroad, runoff drains off the roadway into roadside ditches on either side of the road that carry runoff south towards the lake.

North of the railroad bridge at the intersection of Nichols Rd and W Bella Casa Dr, there is a low point at the NW corner of the intersection that is eroding the gravel and causes ponding on the roadway in larger storm events.

Along Nichols Rd, from the intersection of W Bella Casa Rd to the intersection with W McCulloch Blvd, the site is very flat. There are shallow roadside ditches on both side of Nichols Rd that collect roadway runoff. Driveways with access from Nichols Rd either have small driveway culverts or have been graded with a v-pan to convey flows ditch flows across or under the driveways.

The new trail is proposed north of W McCulloch Blvd to connect to the existing trail system. The trail is located in an area that is currently a large undeveloped field with no defined drainage ways. Runoff in this area likely infiltrates into the ground or ponds in local depressions.

Proposed Drainage In areas where the new trail and road are being constructed parallel, an 8” ditch will be graded in between the road and sidewalk based on geometric constraints to capture and convey roadway runoff. Driveways that are being impacted by the construction will be replaced with a v-pan graded in to allow flow to drain across in a low maintenance/cost effective but controlled manner. On the south side of W Bella Casa Drive an 18" culvert is proposed under the pedestrian trail to convey flow from the 8" roadside ditch to existing drainage patterns on the west side of the trail.

Hydraulics Ditch and culvert capacity have not been evaluated for the proposed design. Since there are minimal drainage components in place currently, proposed drainage will improve overall drainage conditions while perpetuating existing drainage patterns.

Stormwater Quality and Erosion Control A Stormwater Pollution Prevention Plan (SWPPP) and erosion control plans have been prepared for this project detailing how stormwater will treated to prevent sediment and pollution from leaving the site and contaminating nearby sources. No permanent water quality is proposed, Summary The proposed project will improve continuity and safety for pedestrians, bicyclists, and vehicles between Lake Pueblo State Park and the existing trail system to the north. The proposed drainage improvements are minimal and will mimic existing drainage patterns.

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Appendix A

Supporting Maps

COKOENIG

Rectangle

Appendix B

Soil Maps

Hydrologic Soil Group—Pueblo Area, Colorado, Parts of Pueblo and Custer Counties (Nichols Rd Soil Reports)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

2/12/2020

517800 518200 518600 519000 519400 519800 520200

517800 518200 518600 519000 519400 519800 520200

38° 18' 56'' N

4°

7'

4' ' W

38° 18' 56'' N

4°

6'

'' W

38° 17' 0'' N

4°

7'

4'

' W

38° 17' 0'' N

4°

6'

'' W

N

Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 13N WGS84 0 500 1000 2000 3000

Feet 0 250 500 1000 1500

Meters Map Scale: 1:17,400 if printed on A portrait (8.5" x 11") sheet.

MAP LEGEND MAP INFORMATION

Area of Interest (AOI) Area of Interest (AOI)

Soils Soil Rating Polygons

A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Lines A

A/D

B

B/D

C

C/D

D

Not rated or not available

Soil Rating Points A

A/D

B

B/D

C

C/D

D

Not rated or not available

Water Features Streams and Canals

Transportation Rails

Interstate Highways

US Routes

Major Roads

Local Roads

Background Aerial Photography

The soil surveys that comprise your AOI were mapped at 1:24,000.

Please rely on the bar scale on each map sheet for map measurements.

Source of Map: Natural Resources Conservation Service Web Soil Survey URL:

Coordinate System: Web Mercator (EPSG:3857)

Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required.

This product is generated from the USDA-NRCS certified data as of the version date(s) listed below.

Soil Survey Area: Pueblo Area, Colorado, Parts of Pueblo and Custer Counties Survey Area Data: Version 18, Sep 13, 2019

Soil map units are labeled (as space allows) for map scales 1:50,000 or larger.

Date(s) aerial images were photographed: Aug 14, 2018—Sep 23, 2018

The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident.

Hydrologic Soil Group—Pueblo Area, Colorado, Parts of Pueblo and Custer Counties (Nichols Rd Soil Reports)

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

2/12/2020

Hydrologic Soil Group

Map unit symbol Map unit name Rating Acres in AOI Percent of AOI

Ha Haversid silt loam, 0 to 2 percent slopes, frequently flooded

B 3.5 0.9%

MaB Manvel silt loam, 2 to 6 percent slopes, dry

B 326.9 87.9%

PM Penrose-Minnequa complex, 1 to 15 percent slopes, dry

D 41.6 11.2%

Totals for Area of Interest 372.0 100.0%

Description

Hydrologic soil groups are based on estimates of runoff potential. Soils are assigned to one of four groups according to the rate of water infiltration when the soils are not protected by vegetation, are thoroughly wet, and receive precipitation from long-duration storms.

The soils in the United States are assigned to four groups (A, B, C, and D) and three dual classes (A/D, B/D, and C/D). The groups are defined as follows:

Group A. Soils having a high infiltration rate (low runoff potential) when thoroughly wet. These consist mainly of deep, well drained to excessively drained sands or gravelly sands. These soils have a high rate of water transmission.

Group B. Soils having a moderate infiltration rate when thoroughly wet. These consist chiefly of moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture.

These soils have a moderate rate of water transmission.

Group C. Soils having a slow infiltration rate when thoroughly wet. These consist chiefly of soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture. These soils have a slow rate of water transmission.

Group D. Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet. These consist chiefly of clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material. These soils have a very slow rate of water transmission.

If a soil is assigned to a dual hydrologic group (A/D, B/D, or C/D), the first letter is for drained areas and the second is for undrained areas. Only the soils that in their natural condition are in group D are assigned to dual classes.

Hydrologic Soil Group—Pueblo Area, Colorado, Parts of Pueblo and Custer Counties Nichols Rd Soil Reports

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey

Rating Options

Aggregation Method: Dominant Condition

Component Percent Cutoff: None Specified

Tie-break Rule: Higher

Hydrologic Soil Group—Pueblo Area, Colorado, Parts of Pueblo and Custer Counties Nichols Rd Soil Reports

Natural Resources Conservation Service

Web Soil Survey National Cooperative Soil Survey