Final_Hydraulics_Recommendations_Memo-Point_Reyes.pdf

Point Reyes National Seashore 3R

CA PORE 10(4), 200(1) & 201(1)

Final Hydraulics Recommendations Memorandum

Marin County, California

Prepared for:

U.S. Department of Transportation Federal Highway Administration

Central Federal Lands Highway Division IDIQ Contract No. DTFH68-10-D-00002

Task Order No. T-11-017

December 2014

Prepared by:

707 17th Street, Suite 2300 Denver, Colorado 80202

Project No. WVXW3017

TABLE OF CONTENTS

Page No.

I. Project Description and Location A. Description

B. Location

II. Drainage Basins A. Major Basins B. Minor Basins

III. Drainage Design Criteria A. General Criteria B. Hydrologic Criteria

C. Hydraulic Criteria

IV. Recommended Drainage Structures A. Minor Crossings

B. Major Crossings

V. Erosion Control and Water Quality

VI. Conclusion

VII. References

Appendix

NOAA Isopluvial Maps Precipitation Map Regression Analysis TR-55 Analysis Culvert Summary Table HY-8 Analysis – Existing Conditions HY-8 Analysis – Proposed Conditions Drainage Basin Maps

Final Hydraulics Recommendations Memorandum Point Reyes 3R

I. PROJECT DESCRIPTION AND LOCATION

A. DESCRIPTION

The Central Federal Lands Highway Division (CFLHD), National Park Service (NPS) Pacific West Region (PWR) 3R project for Point Reyes N.S. has proposed various improvements along portions of the following roads: 7.52 miles of Route 10 (Limantour Road), 1.48 miles of Route 200 (Lighthouse Road), and 0.91 miles of Route 201 (Chimney Rock Road) in Marin County, California. Route 10 improvements include repair and stabilization of a landslide area as well as guardrail replacement, pavement resurfacing, and rehabilitation or replacement of many culverts. Route 200 and Route 201 improvements include ADA accessibility of parking areas, cattle guard cleaning, and culvert replacement. Route 201 also includes pavement rehabilitation, restoration, and resurfacing (3R) to increase the pavement width to 12 feet and improve existing pullouts. All culverts on Route 201 will be replaced. The project limits are shown on the following page. Each of these routes is completely within the Point Reyes National Seashore (PRNS).

The existing pavement widths are different for each of the three roads. Route 10 is a two-lane paved roadway with paved widths varying from 23 to 26 feet and variable width unpaved shoulders. Route 200 is a two-lane paved roadway with paved widths varying from 18 to 20 feet and variable width unpaved shoulders. Route 201 is a narrow two way one-lane paved roadway with paved widths varying from 10 to 12 feet and variable width unpaved shoulders.

A scoping and site review meeting was conducted in November 2010 (by others) and a scoping report was completed in June 2011 (Reference 1). Additional field review meetings were conducted in April 2012 following the 30% plan submittal and in August 2012 following the 70% plan submittal. The purpose of the meetings was to review the plans, add site features, review existing culverts, document and review parking pullouts, review guardrail height and end terminals, document signs, utilities, and discuss design requirements with PRNS staff. Part of the site investigation was to determine existing drainage conditions within the project area and to make recommendations for improvements.

During the field review in April 2012, the team examined all culverts noted in the 2011 scoping report as recommended for replacement or repair, noted size and conditions of the pipes and needs for replacement of pipes, end sections, and/or headwalls. The field review in August 2012 allowed the team to confirm the proposed design and focus on additional details such as aquatic organism passage requirements and roadside ditch depth. The purpose of this memorandum is to document the findings of the various field reviews, and to document the final recommendations for the drainage improvements for the project.

LOCATION MAP

B. LOCATION

Route 10 begins at the intersection of Bear Valley Road approximately 1 mile south of Point Reyes Station, California and terminates approximately 7 miles southeast at the intersection with English Way, near the Limantour Beach Parking Lot. The roadway is owned and maintained by the NPS. The route is functionally classified as a Class 1 Principal Park Road serving Limantour Beach and numerous trail heads. Work consists of stabilizing a landslide area, pavement resurfacing, and replacing culverts, signs, and guardrail end terminals.

Route 200 begins at the intersection of Sir Francis Drake Boulevard and Chimney Rock Road on the southwestern tip of the Point Reyes National Seashore, and extends west approximately 1.5 miles to the Point Reyes Lighthouse. The roadway is owned and maintained by the NPS. The route is functionally classified as a Class

Route 200 Route 201

Route 10

3 Special Purpose Park Road providing access to the Sea Lion Overlook and the Lighthouse Visitor Center. Work consists of ADA improvements in the parking area as well as drainage improvements.

Route 201 begins at the intersection of Sir Francis Drake Boulevard and Lighthouse Road on the southwestern tip of the Point Reyes National Seashore, and extends east approximately one mile to the Chimney Rock Parking Lot. The roadway is owned and maintained by the NPS. The route is functionally classified as a Class 3 Principal Park Road providing access to the Elephant Seal Overlook and the Historic Point Reyes Lifeboat Station. Work consists of pavement widening, ADA improvements in the parking area, culvert replacements, and cleaning existing cattle guards.

II. DRAINAGE BASINS

A. MAJOR BASINS

Route 10 crosses over the Inverness Ridge which divides the Point Reyes and Tomales Bay watersheds. The northern 3.4 miles of roadway falls within the Inverness drainage basin which flows northerly to Tomales Bay. In this short segment, the route crosses 7 major drainage features. The route then follows the ridge for approximately 1.1 miles before it crosses into the Point Reyes drainage basin which flows southwesterly to the Pacific Ocean. The project area crosses a few more drainage features as it extends another 2.9 miles southwesterly toward the coastline. The drainage crossings along Route 10 include Haggerty Gulch and additional unnamed drainageways.

Routes 200 and 201 are completely within the Point Reyes watershed in the southwestern tip of Point Reyes National Seashore. This portion of the watershed is flat, narrow, and absent of major drainage features.

B. MINOR BASINS

In addition to the major drainage crossings, there are approximately 25 existing minor culvert crossings within the project area (about 17 on Route 10, 7 on Route 201, and 1 on Route 200). This includes cross culverts for minor basins and ditch relief culverts.

Pipe sizes for these basins range from 12” to 48” in diameter.

III. DRAINAGE DESIGN CRITERIA

A. GENERAL CRITERIA

Hydrology and hydraulics criteria for the Point Reyes National Seashore 3R project is based on the guidelines outlined in Chapter 7 of the Federal Lands Highway Project Development and Design Manual (PDDM) (Reference 2).

B. HYDROLOGIC CRITERIA

Hydrologic analysis for the project was done only in specific locations. These locations were identified to be for larger flow areas (major basins), or areas where further analysis was required to make proper recommendations. Locations were chosen based on field observations of active flow or evidence of erosion at the inlet or outlet of the culvert. Some of the larger culverts also need to be extended upstream or downstream to be able to construct a milder and safer slope from the edge of pavement to the top of pipe or headwall. For these locations, two different hydrologic methodologies were used, depending on basin size.

The USGS National Streamflow Statistics (NSS) program uses current statewide regression equations to estimate flood magnitude and frequency on ungaged watersheds. The NSS recently replaced the National Flood Frequency (NFF) program. A recent update of the regression equations and hydraulic regions for the state of California was released in a July 2012 report (Reference 3) where 30 years of additional flood gage data have been analyzed. The software program developed by NSS to estimate flood magnitude and frequency would normally be used in this instance, but the software does not include this latest change. Instead, the regression equations from the July 2012 report were used to calculate design flows for the project area. California is divided into six hydrologic regions, each with their own regression equations. The project area is within the North Coast Region.

Variables used in the equations are basin area, and mean annual precipitation. This methodology recommends a minimum basin area of 0.04 square miles (26 acres).

Locations where a hydrologic analysis was performed are mostly along major drainageways, and most of the specific basins chosen meet this minimum basin size requirement.

For the basis of comparison, the NRCS TR-55 graphical peak method (Reference 4) was also used to calculate runoff values. This method relies on basin parameters such as soil cover, hydrologic soils group, runoff curve number, area, length, slope, and time of concentration. Rainfall precipitation was based on NOAA (Atlas 2) isopluvial maps for 24-hour storm duration.

These two approaches are consistent with the recommended hydrology guidelines presented in the PDDM. Regression analysis was run on the major basins using the North Coast Region equations. These results were then compared to the results using the TR-55 methodology. The North Coast Region regression equations produced similar runoff values when compared to the TR-55 methodology for the larger basins, but much higher runoff values for the smaller basins, nearly 50% higher. Due to the years of additional precipitation data being gathered and incorporated into the regression equations, these results are considered to be more accurate than the TR-55 methodology. Therefore, the regression equations were used.

The minimum design storm frequency is based on the roadway classification. The three routes are classified as a low-standard road based on the design speed (< 45 mph), current and future Average Daily Traffic (< 1500), and not being designated as critical access roads. Therefore culvert replacements are recommended to be designed for the 25-year storm event, in accordance with Table 7.1-A of the PDDM.

C. HYDRAULIC CRITERIA

Culverts The minimum diameter for replacement culverts crossing the mainline is 24 inches, as stated in the PDDM. Culverts to be replaced on Limantour Road will meet this requirement. Culverts to be replaced on Lighthouse Road and Chimney Rock Road will typically be 18 inches. Most of the existing culverts smaller than 18 inches are to be replaced. In some cases where very little cover is available, this is the largest pipe that will fit, and a design exception will be required. End treatments will typically consist of end sections for minor culverts, but headwalls and wingwalls will be used on the larger pipes. Culvert outlets will include rock riprap outlet protection.

Culvert hydraulic design will be based on the PDDM, with both capacity design and stability design being considered. Headwater to depth ratios (HW/D) up to 1.5 will be allowed. Object markers are to be provided at the end of each proposed culvert.

Riprap Local scour at culvert entrances and outlets was reported in some locations, as well as the need to further stabilize the fill slopes approaching the culverts. The need for riprap protection at the culvert inlets and outlets, stream channels, and adjacent fill slopes was evaluated and designed based on the guidance in HEC-14 (Reference 5).

Inlets Grated inlets will be used in the parking area on Lighthouse Road and in the curb and gutter section on Chimney Rock Road. A drop inlet will be used in the landslide area on Limantour Road. Where underdrains are required along Limantour Road, the new perforated pipe will connect to existing inlets.

Ditches Roadside ditch sections will be utilized in conjunction with the 3R roadway sections.

Roadside ditches will have a vegetative lining to maintain the historic flow characteristics of the existing roadway and are designed based on the guidance in HEC-15 (Reference 6). Ditches will be protected during construction with erosion control devices. Ditch relief culvert crossings are provided where necessary.

Floodplains According to the effective Flood Insurance Rate Maps (FIRMs), there are no mapped 100-year floodplains within the project area.

Aquatic Organism Passage In general, culvert crossings on live (perennial) streams are to be evaluated on whether they need to be designed to accommodate aquatic organism passage.

Although the tributaries crossing Limantour Road are not perennial streams, they do contribute to Lagunitas Creek and there is a possible presence of Steelhead fish in three of the lower culverts of Limantour Road. Two concrete box culverts and one pipe-arch culvert have been designed using the stream simulation method to accommodate potential passage of aquatic organisms. The stream simulation method is intended to mimic the natural stream processes within the culvert. The same natural stream characteristics such as shape, slope, and stream bed material will be provided at the crossings. The bottom of these culverts will be buried with one foot of native material while still meeting the hydraulic capacity requirements.

IV. RECOMMENDED DRAINAGE STRUCTURES

A. MINOR CROSSINGS

During the scoping field review in November 2010, an inventory was taken of the existing drainage culverts along the three project routes. The existing culverts were assessed during the field review and an initial recommendation was given.

During the 30% field review in April 2012 there was further assessment of many of the culverts on a location by location basis. Existing culverts were inspected for condition, hydraulic adequacy, and erosion problems. In general, the minor culverts were structurally intact but require cleaning to remove sediment and debris. Some of the culverts require end section improvements as well as regrading to repair the effects of scour. Final recommendations are summarized as follows:

Limantour Road (Route 10) Station 27+06 The existing crossing is a 36” CMP that is corroded and has a damaged end section on the upstream side of the culvert. The culvert should be replaced with a 36” culvert with end sections.

Station 36+28 The existing crossing is a 42” CMP with a 36” HDPE lining. A hydrologic and hydraulic analysis was performed and a replacement 42” CMP is recommended.

The culvert should be improved with new end sections and riprap aprons upstream to armor the channel from the side tributary and downstream to eliminate ponding.

Station 36+35 The existing 18” CMP conveys a small tributary directly to the 42” lined culvert crossing Limantour and has undermined the upstream end section. The culvert should be protected in place. The proposed riprap apron at the upstream end of the 42” CMP will mitigate the erosion potential.

Station 45+62 The existing crossing is an 18” x 24” pipe-arch CMP. The culvert is in good condition but has dense vegetation and sedimentation build-up at the outlet. The culvert should be cleaned.

Station 51+25 The existing crossing is an 18” x 24” pipe-arch CMP. The culvert is in good condition but has dense vegetation and sedimentation build-up at the outlet. The culvert should be cleaned.

Station 55+40 The existing driveway culvert is an 18” CMP parallel to Limantour Road. The culvert is crushed midway and should be replaced in kind.

Station 79+96 The existing crossing is a 24” CMP with a concrete headwall on the upstream end of the pipe. A perforated pipe discharges into a ditch upstream of the CMP, which has cut a channel. It is recommended to place riprap at the upstream side of the culvert to mitigate the erosion potential.

Station 85+50 The existing crossing is a 24” CMP. The inlet upstream should be cleaned of sediment and the apron downstream should be repaved to prevent further erosion.

Station 97+60 The existing crossing is a 24” CMP. The culvert is in good condition, but the upstream approach is experiencing erosion. A riprap apron should be installed upstream of the culvert.

Station 101+26 There are two existing crossings at this location but only one is active. The abandoned crossing has a concrete headwall and has been covered with boards on the upstream side. The active culvert is a 24” CMP with stacked boulders as a headwall on the upstream side. The culvert is in good condition, but the upstream approach is experiencing erosion. A riprap apron should be installed upstream of the culvert.

Station 109+00 to 112+50 Underdrains are present along the upstream side of the road and connect to cross culverts at existing inlets, but it appears that no underdrains are present beyond Station 109+00. Groundwater bleeds through the pavement for this 300-foot stretch of pavement. Underdrains should be installed on the upstream side of the road from Station 109+00 to the end of the bluff at approximate Station 112+50 to draw groundwater away from the pavement and to convey it to the existing cross culverts.

Station 187+68 The existing crossing is a 24” CMP with an end section on the upstream side of the pipe. The culvert is corroded and should be replaced with a 24” CMP with end sections. Reconditioning of the upstream ditch is also recommended.

Station 207+00 to 207+20 The existing crossing is a 24” CMP with plastic lining. The culvert is in good condition, but the upstream ditch is not well defined and has been partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended.

Station 213+25 to 213+45 The existing crossing is a 24” CMP with plastic lining. The culvert is in good condition, but the upstream ditch is not well defined and has been partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended.

Station 229+12 to 229+32 The existing crossing is a 12” CMP with plastic lining. The culvert is in good condition, but the upstream ditch is not well defined and has been partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended and the culvert should be cleaned.

Station 248+67 to 248+87 The existing culvert is an 18” CMP with plastic lining. The culvert is in good condition, but the upstream ditch is not well defined and has been partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended.

Station 294+00 The existing culvert at the parking area is an 18” CMP that is crushed on the upstream end. The downstream end is completely buried, and the culvert is not operational. The culvert should be replaced with an 18” CMP with end sections.

Station 300+47 to 302+13 The landslide area will require pavement stabilization and drainage improvements.

Approximately 170 feet of underdrain is needed on the upstream side of the road. A new inlet and culvert should be installed to convey roadside drainage and groundwater under the roadway.

Station 321+30 The existing crossing at Route 210 Laguna Road is a 12” CMP. The culvert should be replaced with an 18” CMP with end sections and the outlet should be regraded.

Station 321+40 to 321+65 The existing 12” CMP culvert crossing Laguna Road should be replaced with an 18” CMP with end sections.

Station 339+84 to 340+04 The existing crossing is an 18” CMP. The upstream end is slightly damaged but the culvert is still functional. The upstream ditch has been partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended and the culvert should be cleaned.

Station 370+55 The existing driveway culvert is a 12” CMP. The culvert is in good condition but needs to be cleaned.

Station 372+26 The existing crossing is an 18” CMP. The upstream end is slightly damaged, but the culvert is still functional. The downstream end has sediment build-up and the culvert should be cleaned.

Station 394+45 to 394+65 The existing crossing at Route 500 is an 18” RCP. The culvert is in good condition, but the upstream ditch has been partially filled in with grass and sediment.

Reconditioning of the upstream ditch is recommended and the culvert should be cleaned.

Station 395+15 to 395+35 The existing crossing at Route 404 is an 18” RCP. The culvert is in good condition, but the downstream ditch is not well defined. Reconditioning of the downstream ditch is recommended and the culvert should be cleaned.

Station 404+50 The existing crossing is a 15” RCP with a short extension of 18” CMP on the downstream end of the pipe. The RCP section of pipe is in good condition. The connection between the two materials is not flush and the CMP section is beginning to rust through. The 18” CMP section of pipe should be replaced with 15” RCP so that the culvert is continuous throughout.

Station 405+00 to 405+20 The existing crossing is a 12” CMP. The culvert is in good condition, but the upstream ditch is partially filled in with grass and sediment. Reconditioning of the upstream ditch is recommended.

Station 405+94 The existing crossing is a 12” CMP. The culvert is slightly corroded and should be replaced with a 12” CMP with end sections.

Lighthouse Road (Route 200) No culverts are to be replaced along Lighthouse Road. As part of the parking area reconstruction, a new inlet and culvert will be installed and an existing inlet will be replaced. Since the parking area is located within a No Discharge Zone of the California Ocean Protection Plan (COPP), sheet flow will be directed away from the south edge of the parking area by revised grading and a spill curb. Sheet flow will be collected in one of two inlets and will outlet to the north side of Lighthouse Road, satisfying the requirements in the COPP.

Station 751+60 The existing crossing is an 18” CMP with plastic lining. The culvert is in good condition, but the ditches upstream and downstream are not well defined.

Reconditioning of the upstream and downstream ditches is recommended.

Chimney Rock Road (Route 201) Station 501+24 The existing crossing is a 12” HDPE culvert and should be upsized to a 24” culvert with end sections and riprap aprons at the inlet and outlet. The upstream side of the culvert should be cleared of dense vegetation. A roadside ditch should be graded on the upstream side of Chimney Rock Road from the high point at approximate Station 512+00 to the replacement culvert, conveying runoff away from the roadway and the cattle guards. The cattle guards will no longer collect roadside drainage and convey it under the roadway. The larger diameter culvert will accommodate the additional runoff that is currently conveyed through the cattle guards. During the 70% field review, the potential impacts downstream were evaluated and the existing channel will not be adversely impacted because it currently accepts flow from the cattle guards approximately 100 feet downstream. The existing channel between Chimney Rock Road and the cattle guard outlet is wide and deep enough to accommodate this additional flow.

Station 515+97 The existing crossing is a 16” HDPE. The culvert should be replaced with an 18” culvert with end sections and riprap aprons at the inlet and outlet. A roadside ditch should be graded on the upstream side of Chimney Rock Road from the high point at approximate Station 512+00 to the proposed culvert, conveying runoff away from the roadway.

Station 521+70 The existing crossing is a 16” HDPE. The culvert should be replaced with an 18” culvert with end sections, riprap aprons at the inlet and outlet and relocated to Station 521+06 (west of the aggregate pullout). A roadside ditch should be graded on the upstream side of Chimney Rock Road from approximate Station 516+50 to the proposed culvert, conveying runoff away from the roadway.

Station 527+05 The existing crossing is a 16” HDPE. The culvert should be replaced with an 18” culvert with end sections and riprap aprons at the inlet and outlet. A roadside ditch should be graded on the upstream side of Chimney Rock Road as well as an underdrain system from Station 523+20 to the proposed culvert, conveying runoff away from the roadway. The underdrain system will be constructed beneath the roadside ditch according to the standards. The system will have independent outlet pipes placed between and prior to each culvert (approximately every 200 feet).

Station 531+28 The existing crossing is a 12” HDPE. The culvert should be replaced with an 18” culvert with end sections and riprap aprons at the inlet and outlet. A roadside ditch should be graded on the upstream side of Chimney Rock Road as well as an underdrain system from Station 527+10 to the proposed culvert, conveying runoff away from the roadway. As described for Station 527+05, the underdrain system will be constructed beneath the roadside ditch with independent outlet pipes.

Station 534+18 The existing crossing is a 12” CMP. The culvert should be replaced with an 18” culvert with end sections and riprap aprons at the inlet and outlet. A roadside ditch should be graded on the upstream side of Chimney Rock Road as well as an underdrain system from Station 531+20 to the proposed culvert, conveying runoff away from the roadway. As described for Station 526+98, the underdrain system will be constructed beneath the roadside ditch with independent outlet pipes.

Station 547+16 The existing crossing is an 18” CMP. The downstream end is crushed and the culvert should be replaced with an 18” CMP with end sections and riprap aprons at the inlet and outlet. The upstream and downstream ditches should be regraded.

Currently, some runoff bypasses the culvert flowing around the parking lot in an open ditch. This flow will no longer bypass the 18” culvert but will be captured and directed under Chimney Rock Road. Additional runoff downstream of this culvert on the south side of Chimney Rock Road will be captured in the regraded ditch around the parking lot.

All other minor culverts along these roads are in good condition and listed as “do not disturb” on the plans.

Some specific locations required a more detailed hydrologic and hydraulic analysis.

These crossing are discussed in the major crossings section.

B. MAJOR CROSSINGS

As noted previously, specific locations were identified where hydrologic and hydraulic analysis has been performed. This determination was based on observations made during the field reviews and review of the USGS quadrangle mapping. These major crossings were evaluated based on observations made during previous field reviews, discussions with PRNS maintenance staff, and additional hydrologic & hydraulic analysis. Careful consideration was given to the potential for future corrosion and sediment deposition at the major crossing locations. Recommendations for replacement or other improvements were made based on reducing this potential and designing for a 50-year service life. Each of the identified major crossing locations is discussed below.

Limantour Road (Route 10) Station 12+55 The existing crossing is a double 45” x 29” pipe-arch CMP that has experienced flooding and sediment deposition during major storms on the upstream side of the culverts. PRNS staff mentioned this location as having potential fish passage and a desire to replace the culvert with one that will accommodate fish passage as well as improve maintenance accessibility. Park staff would prefer to access the culvert from the roadway surface rather driving down into the stream bed. A hydrologic and hydraulic analysis was performed to determine the pipe size required hydraulically while also spanning the drainage to allow for fish passage per the Culvert Criteria for Fish Passage by the California Department of Fish and Game (Reference 7). The

CMPs are recommended to be replaced with a 6’ x 4’ concrete box culvert with headwalls and wingwalls and a riprap apron at the outlet. The vertical opening will be 3 feet to allow for one foot of native material along the bottom of the culvert, following the stream simulation method for fish passage. The short vertical height of the culvert is also due to the low roadway clearance available on top of the culvert.

The bottom of the culvert will be buried with one foot of native material.

Station 55+71 The existing crossing has parallel 53” x 34” and 45” x 29” pipe-arch CMPs that have experienced flooding and sediment deposition during major storms on the upstream side of the culverts. PRNS staff mentioned this location as having potential fish passage and a desire to replace the culvert with one that will accommodate fish passage as well as improve maintenance accessibility. A hydrologic and hydraulic analysis was performed to determine the pipe size required hydraulically while also spanning the drainage to allow for fish passage. The CMPs are recommended to be replaced with a 8’ x 5’ concrete box culvert with headwalls and wingwalls and a riprap apron at the outlet. The vertical opening will be 4 feet to allow for one foot of native material along the bottom of the culvert, following the stream simulation method for fish passage. The short vertical height of the culvert is due to the low roadway clearance available on top of the culvert.

Station 60+01 The existing crossing is a 54” CMP with end sections. Severe corrosion has rotted the bottom of the pipe. A steady stream flows under the corroded pipe carrying bedding material with it and washing away the support under the upstream end section. A hydrologic and hydraulic analysis was performed to evaluate the possibility of lining the pipe; however, the lining makes the pipe size inadequate. A 83” x 57” pipe-arch CMP is recommended to better match the width of the channel immediately downstream and to accommodate fish passage. The vertical opening will be 45” to allow for one foot of native material along the bottom of the culvert, following the stream simulation method for fish passage. Headwalls and wingwalls are also recommended to stabilize the bank and prevent erosion and scour. Riprap aprons are recommended at the inlet and outlet to armor the channel from the high velocity flows due to the narrow upstream channel.

Station 76+11 The existing crossing is a 48” CMP with a headwall upstream and riprap aprons upstream and downstream of the culvert. The culvert was recently replaced due to failure after heavy rains that eventually led to roadway failure. The new culvert meets the design requirements of the PDDM and no further improvements are recommended.

Station 88+07 The existing crossing is a very deep CMP with a vertical perforated CMP connecting to it and rising above ground on the upstream side. The riser pipe has rectangular holes cut out of the pipe to allow the collection of both surface and groundwater.

Neither the size nor condition of the horizontal pipe was determined during the field review because it was too deep to measure on the upstream side and the downstream side was not accessible due to steep slopes. The culvert will need to be assessed by PRNS maintenance staff or by the awarded contractor to determine the extent of corrosion, deformation, or joint separation of the pipe. The method of rehabilitation will be determined by the overall condition of the pipe. Options include slip lining or cured in place rehabilitation. The 24” overflow CMP is intact and doesn’t require any improvements.

Station 113+75 The existing crossing is a very deep CMP with a vertical perforated CMP connecting to it and rising above ground on the upstream side. The riser pipe has rectangular holes cut out of the pipe to allow the collection of both surface and groundwater.

Neither the size nor condition of the horizontal pipe was determined during the field review because it was too deep to measure on the upstream side and the downstream side was not accessible due to steep slopes. The culvert will need to be assessed by PRNS maintenance staff or by the awarded contractor to determine the extent of corrosion, deformation, or joint separation of the pipe. The method of rehabilitation will be determined by the overall condition of the pipe. Options include slip lining or cured in place rehabilitation. The 36” overflow CMP with 8” underdrain is intact and doesn’t require any improvements.

Station 141+92 The existing crossing is a 48” CMP. The cross section of the pipe is deformed slightly and the joints appear to be out of alignment. There isn’t any evidence of seepage through the seams, however. A hydrologic and hydraulic analysis was performed to evaluate the possibility of lining the pipe. Results show that a 42” pipe is adequate to carry the 25-year design flow, so lining the pipe is the recommended solution. An end section on the upstream side of the culvert is recommended to prevent undermining. A riprap apron is also recommended at the inlet to prevent erosion. The 36” overflow CMP is intact and does not require any improvements.

Station 162+06 The existing crossing is a 54” CMP. Corrosion has rotted the bottom of the pipe allowing water to flow both through and underneath the culvert. A hydrologic and hydraulic analysis was performed to evaluate the possibility of lining the pipe.

Results show that a 48” pipe is adequate to carry the 25-year design flow, so lining the pipe is the recommended solution. Flowable fill should be used to fill any voids that may exist beneath the culvert inlet. A headwall and wingwalls are recommended on the upstream side to prevent scour. The upstream end should be regraded and improved with a riprap apron. The 48” overflow CMP at Station 162+28 projects on the upstream side and should be shortened by approximately 8 feet to match the toe of slope. Otherwise, the overflow CMP is intact and doesn’t require any additional improvements.

These are the final assessments and recommendations based on the allowable HW/D per the PDDM, which is 1.5 for 48" and smaller, and 1.2 for larger than 48".

Final recommendations are also based on the various field reviews and further discussions with the PRNS staff. Final culvert profiles were designed as needed using the guidelines in the Guide for Designing and Staking Culvert in the Field

(Reference 8). Culvert end treatments, in the form of headwalls or end sections with rock riprap inlet/outlet protection are provided as needed and are shown in the plans.

V. EROSION CONTROL AND WATER QUALITY

An erosion and sediment control plan has been developed for the project, which consists of measures that serve as Best Management Practices (BMP’s) for water quality during construction, as well as permanent measures. The BMP’s for erosion and sediment control focus primarily toward protecting receiving waters and water sources in areas of construction activity. They include controls such as silt fence, inlet protection, and riprap outlet protection at culverts. Roadside ditches will also be protected during construction.

VI. CONCLUSION

The Federal Lands Highway Project Development and Design Manual (PDDM) was used for drainage criteria, with a 25-year recurrence interval used for the analysis of the cross culverts. The recommendations for each minor culvert location have been assessed during the field reviews, and recommendations for major culverts are based on consideration of all pertinent criteria and constraints, with input and acceptance by the appropriate PRNS and CFLHD personnel. The two hydrology methods used, regression analysis and TR-55, are consistent with the PDDM.

VI. REFERENCES

1. Point Reyes National Seashore CA PORE 10(4), 200(1), & 201(1) Project Delivery Plan and National Park Scoping Report, prepared for the USDOT Central Federal Lands Highway Division by Atkins, dated June 20, 2011.

2. Federal Lands Highway Project Development and Design Manual (PDDM), prepared by the Federal Highway Administration (FHWA-USDT), February 2011.

3. Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006, prepared in cooperation with FEMA, 2012.

4. WinTR-55 Computer Program, Urban Hydrology for Small Watersheds, Version

1.00.09, developed by the Natural Resources Conservation Service, dated August 5, 2009.

5. FHWA HEC-14, Hydraulic Design of Energy Dissipators for Culverts and Channels, prepared by the Federal Highway Administration (NHI-06-086), 2006.

6. FHWA HEC-15, Design of Roadside Channels with Flexible Linings, prepared by the Federal Highway Administration (NHI-05-114), 2005.

7. Culvert Criteria for Fish Passage, prepared by the State of California Resources

Agency Department of Fish and Game, dated May 2002.

8. Guide for Designing and Staking Culvert in the Field, prepared by the Central Federal Lands Highway Division, dated January 9, 1996.

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APPENDIX

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OrtizVT Text Box Limantour Road P = 40 inches

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Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006

By Anthony J. Gotvald, Nancy A. Barth, Andrea G. Veilleux, and Charles Parrett

Abstract Methods for estimating the magnitude and frequency

by regulation or diversions have been updated. Annual

having 10 or more years of data. Flood-frequency estimates

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computed by using a geographical information system.

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region. Flood-frequency estimates and basin characteristics ��9����

used in the regional regression analysis. Five hydrologic

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are functions of drainage area and mean annual precipitation ��������%4��

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standard errors of prediction for the regression equations in all %4��

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regional regression equations are functions of drainage area.

Average standard errors of prediction for these regression equations range from 214.2 to 856.2 percent.

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6�� ����� �� ������������� ����������������4���������� frequency estimation equations for urban streams because of the limited number of sites. Flood-frequency estimates for frequency estimates for 630 non-urban sites.

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4 Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006

120°122°124°

42°

40°

38°

36°

34°

COAST RAN

GES

COAST RANGES

KLAM

ATH

M

OUNTAINS

SIERRA

NEVADA

TRANSVERSE RANGE

Subtropical Pacific moisture

Pacific moisture

SAN GABRIEL/SAN BERNARDINO

RANGES

CASCADE

RAN

GE

Physiographic Region

Hydrologic Region—Desert

EXPLANATION

California Coast Ranges

California Trough

Great Basin

Klamath Mountains

Los Angeles Mountains

Mexican Highlands

Salton Trough

Sierra Nevada

Sonoran Desert

Middle Cascade Mountains

Lower Californian Province

0 75 150 MILES

0 75 150 KILOMETERS

CAL I FORN I A

OREGON

N E V A D A

A R I Z O N A

PACIFIC OCEAN

Base modified from U.S. Geological Survey (USGS) 1:100,000-scale digital data Shaded relief from USGS National Elevation Dataset (NED)

Figure 1. Physiographic regions in California (Fenneman and Johnson, 1946).

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Data Compilation 5

Table 1. Basin characteristics considered for use in regional regression analysis for California.

Name Description Unit Data source

���"��" Drainage area of the basin Square miles $% ��������������� http://www.horizon-systems.com/NHDPlus/

("�������� Perimeter of the basin Miles $% ��������������� http://www.horizon-systems.com/NHDPlus/ minimum elevations in the basin

Feet $% ��������������� http://www.horizon-systems.com/NHDPlus/

http://www.horizon-systems.com/NHDPlus/

�)�/��� Minimum elevation in the basin Feet $% ��������������� http://www.horizon-systems.com/NHDPlus/

)"1�"��" Percentage of basin area covered by lakes and ponds

Percent 2%%3���� ��� �)����4���������,����5�)4�67 )����4�����http://www.mrlc.gov/nlcd2001.php

�)8%%% Percentage of basin area above ���� ����+�8�%%%�+���

Percent $% ��������������� http://www.horizon-systems.com/NHDPlus/

9:;)�;�)�/ Elevation at the outlet of the basin Feet $% ��������������� http://www.horizon-systems.com/NHDPlus/

basin perimeter

Feet per mile $% ��������������� http://www.horizon-systems.com/NHDPlus/

���;249"�; Distance from basin centroid to coast along a line perpendicular �����������4�

Miles $% ��������������� http://www.horizon-systems.com/NHDPlus/

�)�/ Average basin elevation Feet $% ��������������� http://www.horizon-systems.com/NHDPlus/

(�)���$%� Average basin slope Percent $% ��������������� http://www.horizon-systems.com/NHDPlus/

*9���; Percentage of basin area covered by forest

Percent 2%%3���� ��� �)����4���������,����5�)4�67 ���'����4������http://www.mrlc.gov/ nlcd2001.php

�����/ Percentage of basin area covered by impervious surface

Percent 2%%3���� ��� �)����4���������,����5�)4�67 Percent Impervious http://www.mrlc.gov/ nlcd2001.php

���4�� Mean annual precipitation Inches <%% ���������� �� ���������3=>3?2%%%����� http://www.prism.oregonstate.edu/products/

@"��"0 "���� temperature in the basin

Degrees Fahrenheit <%% ���������� �� ���������3=>3?2%%%����� http://www.prism.oregonstate.edu/products/ temperature in the basin

Degrees Fahrenheit <%% ���������� �� ���������3=>3?2%%%����� http://www.prism.oregonstate.edu/products/

)9�B&4��; )�� ������+�����,�� ��'����� � Degrees $% ��������������� http://www.horizon-systems.com/NHDPlus/

)";&4��; )�� ������+�����,�� ��'����� � Degrees $% ��������������� http://www.horizon-systems.com/NHDPlus/

6 Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006 was found to have errors in the stream network that resulted in drainage basin errors in portions of the upper Sacramento River Basin, including some parts of the Pit and Feather River drainages. The basin characteristics computed using a geographic information system (GIS) were used for all streamgages in the study, but some streamgages in the upper Sacramento River Basin were eliminated from further analysis because of potential inaccuracies in the computed basin char-acteristics. Streamgages were eliminated from further analysis if the GIS-calculated drainage areas differed substantially from those published in the NWIS peak-flow database. Differences in drainage area were considered substantial if they exceeded 50 percent for drainage basins smaller than 0.1 square mile, 20 percent for drainage basins between 0.1 and 1 square mile in size, and 10 percent for basins greater than 1 square mile in size. These criteria resulted in 771 streamgages that were considered for further use in the study (pl. 1; table 2).

Streamgages that were excluded from analysis because they did not meet the criteria for drainage area differences included 23 streamgages for which flood-frequency characteristics were previously reported by Parrett and others (2011). Because of the limitations of the NHDPlus dataset, users are cautioned to verify basin boundaries and drainage areas computed at ungaged sites to ensure that results are reasonable.

Flood Magnitude and Frequency at Streamgages

A frequency analysis of annual peak-flow data collected at a streamgage provides an estimate of the flood magnitude and frequency at that specific stream site. Flood-frequency flows were described in previous USGS reports as T-year floods based on the recurrence interval for the flood quantile (for example, the “100-year flood”). The use of recurrence-interval terminology is now discouraged because it can be confusing to the general public. The term has been interpreted to imply a set time interval between floods of a particular magnitude, when in fact floods are random processes that are best understood by using probabilistic terms. While the T-year recurrence interval flood is statistically expected to occur or be exceeded, on average, once during the T-year period, it may be equaled or exceeded multiple times during the period or not at all.

Terminology associated with flood-frequency estimates is shifting away from the T-year recurrence interval flood to the P-percent annual exceedance probability (AEP) flood. The use of percent AEP flood is now preferred because it conveys the probability, or odds, of a flood of a given magnitude being equaled or exceeded in any given year. For example, a 1-percent AEP flood (formerly known as the “100-year flood”) corresponds to the flow magnitude that has a 0.01 probability of being equaled or exceeded in any given year. The P-percent is computed as the reciprocal of the recurrence interval “T” multiplied by 100 (for example, 1/100 × 100 = 1 percent).

T-year recurrence intervals with corresponding percent AEPs are listed in table 3 (Gotvald and others, 2009).

Table 3. T-year recurrence intervals with corresponding P-percent annual exceedance probabilities for flood-frequency flow estimates.

T-year recurrence interval

P-percent annual exceedance probability

2 50

5 20

10 10

25 4

50 2

100 1

200 0.5

500 0.2

Table 2. Summary of streamgages in California that were considered for use in the regional regression analysis, 2006.

[Table 2 is available in a Microsoft© Excel spreadsheet and can be accessed and downloaded at http://pubs.usgs.gov/sir/2012/5113/]

Table 4. Flood-frequency statistics for streamgages in California that were considered for use in the regression equations, 2006.

[Table 4 is available in a Microsoft© Excel spreadsheet and can be accessed and downloaded at http://pubs.usgs.gov/sir/2012/5113/]

Flood-frequency estimates for streamgages are computed by fitting a known statistical distribution to the series of annual peak flows. The statistical distribution commonly used in the United States is the log-Pearson Type III distribution (hereafter referred to as the LP3 distribution). Guidelines and computa-tional methods for using the LP3 distribution are described in Bulletin 17B of the Hydrology Subcommittee of the Interagency Advisory Committee on Water Data (1982). General procedures for fitting the LP3 distribution, the expected moments algorithm (EMA), a new method for statistically detecting multiple potentially influential low outliers when fitting the LP3 distribution, a special application of the LP3 method developed for the desert region of California, and a trial application of a mixed-population flood-frequency analysis for high-elevation streamgages in the California mountains are described in the following sections of the report. The final flood-frequency estimates from the LP3 analysis for the 771 streamgages in California considered in this study are given in table 4.

Flood-frequency estimates could not be computed for station 11067000 Day Creek near Etiwanda, Calif. (map identification number 122), because of the uncertainty of debris flow effects on some of the higher annual peak flows. Also, estimates could not be computed for station 11142500 Arroyo De La Cruz near San Simeon, Calif. (map identification number 219), because of the uncertainty of the indirect-discharge measurements used to determine the larger annual peak flows.

http://pubs.usgs.gov/sir/2012/5113/ http://pubs.usgs.gov/sir/2012/5113/

12 Methods for Determining Magnitude and Frequency of Floods in California, Based on Data through Water Year 2006

Estimation of Flood Magnitude and Frequency at Ungaged Sites set of equations for estimating the magnitude and frequency

measured basin characteristics of the associated drainage use in the regional regression analysis (table 4).

Regression Analysis

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