2020-03-10_Ice House Final Hydraulics Recommendations Memorandum.pdf

H Y D R A U L I C S M E M O R A N D U M

Hydraulics Memorandum for Ice House Road CA

FLAP ED CR147(2)

PREPARED FOR: Wendy Longley/CFLHD

PREPARED BY: Julie Trumpoldt/Jacobs

Virginia Ortiz/Jacobs

DATE: March 10, 2020

Introduction This memorandum presents the field site observations and subsequent hydraulic recommendations for the project corridor located in the Eldorado National Forest in Central California. The 3R project consists of roadway improvements including paving, signing, striping, and guardrail to improve traffic safety. The project limits extend from the intersection with Peavine Ridge Road near MP 6.32 to Wentworth Springs Road near MP 23.94.

Existing Conditions The roadway is generally a consistent 24-foot width throughout. The road has very limited shoulder width and steep edges in this mountainous area. The existing clear zone is 1 foot minimum, but typically 3-5 feet. There are several areas where the pavement edge is worn due to steep embankments and shoulders where the material supporting the pavement was insufficient. Sections of steep cuts into a tall rocky hillside are present within the project limits

Proposed Conditions The proposed project involves rehabilitating the existing pavement within the same footprint. All existing cross culverts were assessed at the 30% field review in June of 2018 to determine if they should be replaced, repaired, or left as is in order to adequately function for the remaining service life of the road.

The scoping report completed in June 2015 states that the existing drainage conditions along the project area are generally good and that a formal drainage analysis is neither necessary nor recommended for the proposed improvements.

HYDRAULICS MEMORANDUM FOR ICE HOUSE ROAD CA FLAP ED CR147(2)

Roadway Hydraulics Design Values

FLH

Standard

Used on This Project

Culvert Design Flood 50-year flood not analyzed

Roadside Ditch Design Flood 10-year flood not analyzed

Pavement Drainage Design Flood

10-year flood, 50-year in sumps not analyzed

Storm Drain Design Flood 10-year flood, 50-year in sumps N/A

El Dorado County does not have any local design standards that will supersede the PDDM. The PDDM was used for design guidance. Normally, the 50-year flood would be used for hydraulic design of a high-standard road (current and projected ADT >2,000), but no drainage analysis was performed for this project.

The project is not within a FEMA regulated floodplain.

There are five major culverts within the project area ranging from 48” to 60” in diameter. All of the major culverts appear to be hydraulically adequate and in good to fair condition. There are no proposed changes or replacements for these major culverts.

In addition to the major crossings, there are approximately 115 minor culvert crossings within the project area, ranging from 12” to 42” in diameter. Most of the culverts are in fair to good condition and appear to be hydraulically adequate and functioning well. County maintenance personnel were not aware of any specific areas of concern. However, it is estimated that at least 3 minor culverts will need replacement, based on being crushed, rusty, or corroded (summarized below). For culverts being replaced, the minimum size pipe diameter recommended by the PDDM is 24 inches, which will be used where adequate cover exists. If there is not adequate cover to accommodate a 24-inch culvert, the largest feasible culvert will be installed. In most situations this is an 18-inch culvert.

• STA 2028+25 The existing 18” corrugated metal pipe (CMP) culvert at this location is buried. It is recommended to replace the pipe in kind, add Class 1 riprap, and redistribute the larger riprap at the outlet.

• STA 2738+10 The existing 18” corrugated metal pipe (CMP) culvert under the access road shows evidence of corrosion. It is recommended to replace the pipe with a 24” equivalent arch pipe to maintain appropriate cover due to the roadway geometric constraints.

• STA 2860+25 The existing 18” corrugated metal pipe (CMP) culvert at this location has evidence of corrosion at the bottom of the pipe. It is recommended to replace the pipe.

It is also recommended to install an additional 24” culvert at Station 2614+00 to adequately channel runoff in a roadside ditch. In addition to some of the culverts being replaced, the object markers noting the milepost should be replaced at all existing culverts.

HYDRAULICS MEMORANDUM FOR ICE HOUSE ROAD CA FLAP ED CR147(2)

Many of the minor culverts have drop inlet structures composed of a vertical section of corrugated metal pipe (36” diameter). These inlet drop structures have experienced sediment and/or debris and will need to be cleaned to restore functionality. In addition, all existing culverts will be cleaned as a part of the project.

Several asphalt berms/blocks were located along the project. It is recommended to remove these blocks as noted in the plans because it appears they cause excessive debris collection, while also reducing the efficiency of the ditch network along the project corridor. The removal of these asphalt elements should provide free flow and assist with the self-cleaning aspect of the culverts.

Due to the natural springs along the mountainside, groundwater is flowing below the roadway and pumping through the section from underneath. It is recommended to install underdrains as noted in the plans to capture this flow to minimize deterioration of the subgrade.

Roadside drainage will be improved by the proposed project by providing clearing for an approximate 4-foot width beyond the edge of shoulder. Many existing earthen ditches will need to be reconditioned, graded to drain, or have their flowlines reestablished. The existing asphalt curb with 4-foot paved ditch is generally in good condition. Portions of this edge treatment will need to be resurfaced and the asphalt curb replaced.

Since the calculated quantities for Class 2 riprap were extremely small in comparison to Class 1, it was decided to use Class 1 riprap for the entire project. Mainly because the quarry haul length/availability is a concern for such a minimal amount of different D50 riprap size. This was discussed and agreed upon by CFL and Jacobs.