Hydraulics.pdf

SIERRA VISTA LANE

FINAL HYDRAULICS REPORT

NV‐FLAP‐100(1)

August 2017

Prepared for:

Federal Highway Administration – Central Federal Lands Highway Division 12300 W Dakota Avenue Lakewood, CO 80228

Prepared by:

Muller Engineering Company 777 South Wadsworth Boulevard Suite 4‐100 Lakewood, Colorado 80226 303.988.4939

Muller Project Number: 15‐043.02

Federal Highway Administration – Central Federal Lands Highway Division

August 2017 Final Hydraulics Report

Table of Contents Page i

Table of Contents

1 INTRODUCTION

1.1 Location

1.2 Project Background and Objectives

1.3 Criteria

2 EXISTING CONDITIONS

2.1 General

2.2 Problem Areas

2.3 Hydrologic analysis

2.4 Existing Deficiencies

2.5 Environmental Findings

3 PROPOSED DESIGN

3.1 General

3.2 Roadway Adjustments

3.3 Culvert Upgrades

3.4 Inlets

3.5 Spread Capacity

3.6 Summary of proposed design elements

3.7 Sediment Considerations

3.8 Streambank stabilization

4 CONCLUSIONS

5 REFERENCES

APPENDICES

August 2017 Final Hydraulics Report

Table of Contents Page ii

Appendices

A. Criteria

B. Photographs (from September 2015) Floodplain Information

Water Quality Data

C. Basin map Existing hydrologic computations

D. Existing hydraulic computations

Summary of Drainage Basin and Existing Capacities

E. Proposed drainage basin map

Proposed hydraulic computations and culvert upgrades Summary of proposed culvert design Proposed Spread and Street Capacity Calculations

August 2017 Final Hydraulics Report

Introduction

1 INTRODUCTION

The proposed drainage design for this project includes improvements to address drainage issues along the project corridor as discussed and reviewed during the project scoping site visit. These improvements include providing new systems where needed, upgrading existing cross culverts, providing riprap bank protection along specific reaches of the Carson River, and improving water quality outlet structures.

While the proposed drainage improvements substantially improve the existing drainage system, the design does not meet design criteria at all locations due to large tributary flows and project constraints

(ROW, environmental impacts, and budget). Overtopping of the road will still occur in select locations.

We (Muller, in coordination with Carson City and FHWA) have used our professional judgement to determine how to effectively implement drainage improvements, however, the drainage design does not meet criteria in all locations.

1.1 Location

Sierra Vista Lane is located east of Carson City, Nevada along the eastern side of the Carson River

(Figure 1). The project extends from the intersection with Pinion Hills Road on the north end, and south for 2.5 miles to near the Rio Vista Lane intersection. Sierra Vista Lane (SVL) provides access to Federal Lands, including for recreational purposes.

August 2017 Final Hydraulics Report

Existing Conditions

1.2 Project Background and Objectives

The purpose of the project is to provide a safe and improved access to Federal Lands. The project includes improvements to the roadway and drainage. In 1997, a major storm (nearly 100‐yr) nearly flooded out SVL. In 2011, another flood left significant debris and sediment on the roadway surface, making SVL impassable. The aging roadway surface is deteriorating, creating safety hazards such as large potholes. Inadequate drainage facilities are impacting erosion that further degrades the roadway surface. Carson City is concerned with the frequency of roadway flooding and subsequent maintenance frequency. The project will reconstruct 2.5 miles of SVL with asphalt pavement overlay and improve existing parking areas, and upgrade the existing drainage system. The project also includes stabilization areas along the Carson River bank.

1.3 Criteria

The project team reviewed the Federal Highway Administration/Central Federal Lands criteria

(Reference 1) and Carson City drainage criteria (Reference 2) to establish the project’s hydrologic and hydraulic design criteria. These criteria are summarized in Appendix A. In general, the criteria for proposed culvert upgrades under Sierra Vista Lane is a 25‐year flood event.

2 EXISTING CONDITIONS

2.1 General

Numerous dry drainage channels and hillslopes flow west towards Sierra Vista Lane before flowing into the Carson River. These drainages are unnamed and range in basin area from approximately 5 acres to

400 acres. Due to the semi‐arid climate of the region, these drainages can be expected to have high natural sediment yields. The recreational activity along Sierra Vista Lane and corresponding vehicular activity within the basins and drainageway paths themselves further increases sediment entrainment.

Vegetation is sparse in this desert landscape with shrubs and junipers (see photos in Appendix B) which leads to generally higher runoff and sediment yields. Soils information can be found in Appendix C.

Sierra Vista Lane runs along the eastern side of the Carson River. The Carson River in this area is a Federal

Emergency Management Agency (FEMA) Zone AE Regulatory floodplain with a regulatory Floodway for a portion of the project reach (Reference 3). See floodplain map in Appendix B. Portions of Sierra Vista

Lane are located within the floodplain between roadway station 1086+00‐ 1100+00. Regulatory water surface elevations (or approximations of) were compared to the survey roadway data to confirm how the floodplain relates to Sierra Vista Lane. The floodplain is against the roadway embankment in the northern portion of the project area from 1175+00‐1170+00.

August 2017 Final Hydraulics Report

Existing Conditions

2.2 Problem Areas

A scoping visit in October 2015 identified areas where drainage problems exist and need evaluation. The areas of evaluation are identified in the table and also in Appendix C. The location(s) of problem areas are identified by distance in miles from the northern end of the project (intersection with Pinion Hills Road) and also by project roadway station. Runoff from concentrated drainage channels and adjacent hillslopes flood onto Sierra

Vista Lane and carry sediment. This sediment either clogs existing culverts, fills roadside ditches, and/or deposit onto the road surface. Both the sediment and water flow is contributing to deterioration of the road surface. Existing drainage infrastructure appears to be undersized for the flows that frequently occur in these channels and off the hillslopes, especially when considering the high sediment yield. In some locations, there is a steep cut slope or natural slope on the uphill side of SVL. This restricts the size of uphill roadside ditches and depressions needed for culvert entrances. Near roadway station 1163+00, the road is entirely in cut and acts as an extension of the upstream offsite drainage channel. Similarly, near roadway station 1104+00, sediment build up on the road and subsequent cleaning has left a berm on the river side of the road, trapping runoff from the upslope offsite drainage channel.

In addition to the areas along the road, there are adjacent parking areas (roadway stations 1174+00 and

1127+00) that have been evaluated for improvements to separate vehicles and drainage in hopes of limiting localized sediment entrainment. Adjacent to station

1174+00, and 1103+00‐1110+00, bank stabilization due to overtopping SVL runoff was also evaluated along the

Carson River.

Identified Drainage problem locations along Sierra Vista Lane

Miles (distance from North end)

Design Point ID/Abbreviated Roadway Station

0.18 1174

0.32 1165

0.39 1160

0.72 1145

0.95 1130

1.07 1126

1.22 1118

1.33 1111

1.37 1108

1.42‐1.48 1110‐1104

1.52 1109

1.56‐1.63 1104‐1097

2.28 1063

2.36 1058

Example of road surface deterioration

August 2017 Final Hydraulics Report

Existing Conditions

2.3 Hydrologic analysis

A hydrologic analysis of the identified problem areas was conducted. To assist in basin delineations, topographic contours were generated from the 1/3 Arc Second (approx. 10m) version of the 3DEP

Program of the National Elevation Dataset (Geographical Information System). Secondary datasets used in the creation of the source data include high resolution flow lines, and water bodies from the National

Hydrography Dataset (NHD). Hydro‐enforcement and generalization can alter the spatial characteristics of the contouring and all basin delineation and other analyses were performed with an understanding of these limitations. The drainage area to each design point (in addition to adjacent sites that seemed important) was delineated (see Appendix C map for the contours and delineations), and is also tabulated in Appendix C. Based upon drainage area size, either the Rational Method or SCS Unit Hydrograph methodology within HEC‐HMS was used to determine the peak flows during 10‐yr, 25‐yr, 50‐yr, and 100‐ yr conditions. Appendix C identifies which hydrologic method has been used for each design point and contains supporting computations.

2.4 Existing Deficiencies

Each existing culvert/design point was evaluated to determine its current capacity prior to overtopping, using the computer program HY‐8. Existing capacities (in cubic feet per second, CFS) are shown in

Appendix D. All culverts are less than a 10‐year capacity, with the exception of the culverts at mile 1.07 and 2.36, which have 25‐year and 10‐year capacity respectively. Design criteria would dictate these to be upgraded to a 25‐year capacity and possibly larger, to account for known sedimentation. However, this may not be feasible due to topographic, right of way, environmental or budgetary constraints. A more detailed evaluation of the existing conditions and problems at each design point are provided below with abbreviated roadway station identifiers:

Sediment filled roadside ditches Undermining of road surface due to overtopping

August 2017 Final Hydraulics Report

Existing Conditions

Sta 1174

There are two culverts/inlets systems at this location. An 18” CMP with a perforated standpipe inlet structure is located in a “detention pond” area. The standpipe allows ponding to occur with slow release of flows through perforations which allows some sediment to deposit. The culvert is receiving storm flows from a 364.2 acre basin. Existing capacity was determined by comparing orifice and weir control calculations on the drop inlet, to the maximum culvert capacity with total headwater. The inlet capacity is 12 CFS but the culvert barrel could take up to 18 CFS with the available headwater. Once capacity is exceeded, water spills down a rundown to the roadway where another drop inlet is located in the roadside ditch. Overtopping water flows over the road and down the embankment near station 1175+11. There is erosion on the river bank at this location with some riprap protection. Flow overtops and travels toward the low point at the bend in the road near station 1175+11, then overtops the roadway.

Sta 1165

The existing culvert is a 24” CMP. The culvert is receiving storm flows from a 64.7 acre basin. Currently, the capacity of this culvert is 15.9 cfs which is equivalent to the 2‐year storm flow rate. The roadway at this location is very flat but is sloping down to the north. There is not a defined low point or channel near the culvert. Once the flows begin to overtop the culvert they will most likely overtop the roadway near station 1165+50 and sheet flow north‐west across the road. The outlet is perched above the hillslope and plunging flows cause erosion.

Sta 1160

The existing culvert is an 18” CMP. The culvert is receiving storm flows from a 14.6 acre basin. Currently, the capacity of this culvert is 8.2 cfs which is between the 5 and 10‐year storm flow rates. This culvert is located adjacent to the low spot in the road. Once the culvert reaches its maximum capacity, the flow will travel directly over the road. The roadway will act as a weir and keep the overtopping flows channeled.

The entrance to this culvert is nearly buried in sediment (see photos, Appendix B).

Sta 1145

The existing culvert is a 42” CMP. The culvert is receiving storm flows from a 237.7 acre basin. Currently, the capacity of this culvert is 33.1 cfs which is less than the 2‐year storm flow rate. This culvert is located at a low point between two dirt roads. The road adjacent to the culvert is a high point so once the culvert reaches its capacity, the flows will most likely split to the north and the south and sheet flow across the road between stations 1145+00 and 1146+10. A small amount of flow will backup into the roadside swales on the north and south side of the culvert. The upstream end of this culvert is nearly buried in sediment

(see photos Appendix B).

Sta 1130

The existing culvert is an 18” CMP. The culvert is receiving flows from an 88.4 acre basin. Currently, the culvert has a maximum capacity of 9.3 cfs which is less than the 2‐year storm flow rate. This culvert is located adjacent to the low point in the road. Once the culvert reaches its maximum capacity, the flow will travel directly over the road. The roadway will act as a weir and keep the overtopping flows channeled.

August 2017 Final Hydraulics Report

Existing Conditions

Sta 1126A

The existing culvert is an 18” CMP in the roadside ditch where a local road crosses to an adjacent parking area and into the 1126 culvert. The culvert is receiving flows from an 11.8 acre basin. Currently, the culvert has a maximum capacity of 2.6 cfs which is less than the 2‐year storm flow rate. The roadway near this culvert is sloping down to the south. Once the culvert has reached its capacity, the flows will spill onto the roadway and sheet flow in the south‐west direction. The flow will travel a maximum of 40’ along the road until it reaches the roadway low point to the south at station 1126+30

Sta 1126

The existing culvert is an 18” CMP. The culvert is receiving flows from a 9.2 acre basin. Currently, the culvert has a maximum capacity of 8.6 cfs which is slightly below the 50‐year storm flow rate. The culvert is located adjacent to a flat section of the road that will not contain overtopping flows very well.

Sta 1118

The existing culvert is a 42” CMP. The culvert is receiving flows from a 202.6 acre basin. Currently, the culvert has a maximum capacity of 51.0 cfs which is less than the 2‐year storm flow rate. The culvert is located adjacent to a low point in the road. Unlike the other low points, this area is flat and wide. Once the culvert reaches its capacity, the flow will spread onto the road and will not be channeled by the roadway configuration. There is significant erosion at the outlet of this culvert, which is perched above the downstream channel invert (see photos in Appendix B). The upstream end of this culvert is nearly buried in sediment.

Sta 1111

There is no culvert at this location, but there is a defined offsite channel that flows to the roadway.

Overtopping water flows south along the roadway and roadside ditch on the west side, and then over the bank into the Carson River, causing erosion (see photos, Appendix B).

Sta 1108

There is no culvert at this location, but there is a defined offsite channel that flows to the roadway. Water flows on the roadway south to the low point near 1107+00 where it eventually overtops into the river

(see photos Appendix B).

Sta 1107

There is no culvert at this location but is a low point in the roadway and channelized offsite flows come to the roadway. Overtopping flows are causing erosion of the Carson River bank on the west side of the roads (see photos Appendix B).

August 2017 Final Hydraulics Report

Existing Conditions

Sta 1104

There is no culvert at this location but it is a localized low point in the roadway profile. A large concentrated offsite channel flows to SVL at this location. The water overtops the road, ponds and deposits sediment, before eventually overtopping into the Carson River. There is erosion on the river bank at this location. Removal of sediment from the roadway here has left a berm on the west side of the road (river side). This acts to further trap and pond water.

Sta 1009

There is no culvert at this location but it is a localized low point in the roadway profile. A large slope on the uphill side contributes offsite runoff into this area. Water overtops into the floodplain on the west side of the road.

Sta 1063

The existing culvert is a 24” CMP with a perforated standpipe drop inlet and “Beehive” grate. The culvert is receiving flow from a 398.5 acre basin. Currently, the culvert has a maximum capacity of 48.4 cfs, but the inlet itself is limited to 21 cfs with the available maximum head. The perforations allow for ponding and slow release of flows to allow some settling of sediment. This culvert is located adjacent to a bend in the road that is sloping down to the south. Once the culvert has reached its capacity, the flow will travel south along the road until it reaches the low point in the road. Once it reaches this point, the flow will overtop the road down the road embankment. The culvert discharges onto a steep channel downstream and there is significant erosion.

Sta 1058

The existing culvert is a 15” CMP. The culvert is receiving flow from a 30 acre basin. Currently, the culvert has a maximum capacity of 16.1 cfs which is slightly above the 10‐year storm flow rate. The culvert is located next to a portion of roadway that is sloping down to the north. Once the culvert reaches its

Sediment accumulation on SVL, near 1104

August 2017 Final Hydraulics Report

Existing Conditions maximum capacity, the flow will enter the roadside swale and travel north. The flows will begin overtopping the roadway as it travels north until it reaches the low point where all the flow will cross the road.

2.5 Environmental Findings

2.5.1 Water Quality

The Carson River adjacent to the project area is an Impaired Water on the Nevada State 303(d) list for the following constituents:

E coli

Mercury in fish

Dissolved Oxygen

Water Temperature

A page from the 303(d) report is included in Appendix B. The water quality within the ephemeral drainages in the project area that are tributary to the Carson River is not known. During flood events, high sediment concentrations and turbidity is assumed.

Naturally high sediment yields from the tributaries to the Carson River is to be expected. However, the project design will be mindful of not increasing sediment yields to the river due to recreational activity, and attempts to allow sedimentation before flows reach the river. However, some conveyance of sediment to the river is to be expected if the project goals are to be met.

2.5.2 Wetlands

ERO Resources has identified wetlands within the project area (Reference 4). As expected, wetlands are only located in fringe areas along the Carson River. The ephemeral drainages tributary to the river and where culverts under Sierra Vista Lane are located, do not contain wetlands. More detail can be found in

Reference 4.

2.5.3 Fish Passage

The ephemeral drainages in the project area do not support fish, so fish passage evaluations will not be necessary. Any fish in the Carson River adjacent to the project site has not been evaluated but will not be impacted with this project.

2.5.4 Stream Restoration

There are sections of eroding streambank adjacent to SVL on the Carson River. The slope between

1103+00‐1108+00 is in particular need of restoration. There is severe erosion occurring on the downslope side of the ephemeral drainage culvert at 1063+00. There is also a reach near 1174+00 where roadway overtopping flows are causing erosion of the upper portions of the Carson River bank.

August 2017 Final Hydraulics Report proposed DESIGN

3 PROPOSED DESIGN

3.1 General

Due to high sediment yields and peak flows from the steep adjacent drainageways, the general proposed design of drainage improvements consists of the following:

Where large offsite channels are flowing towards SVL, culvert those flows underneath the roadway to the other side immediately

Upsize cross culverts as much as possible (up to 25‐year) given topographic, right of way, environmental and budgetary constraints to lessen frequency of roadway overtopping

Be mindful of sediment yield to the Carson River and consider ways to settle sediment before reaching river

Roadside ditches used only for conveyance of localized hillslope runoff; not significant offsite flows

Slope (super‐elevate) the roadway towards the river in areas of flat roadway longitudinal gradient to facilitate sediment movement off the road surface, where feasible

Adjust the roadway profile to better define overtopping locations, consolidate low points, or create more ideal drainage divides.

Extend the pavement section and construct curb and gutter along uphill ditches where erosion has been observed

The general design includes roadside ditches that convey water to inlets and cross culverts. Cross culverts and inlets are located strategically to intercept stormwater and reduce pavement drainage and route drainage within ditches. Many of the ditches will need to be created, and therefore, their capacity has been maintained.

Based on the applicable criteria for the project (shown in Appendix A), the minimum proposed culvert size for the project is 24”, and the minimum proposed storm drain pipe size is 18”. For the purposes of the proposed design, culverts were defined as pipes that have free inlets and outlets, and storm drain was defined as pipes that are connected to an upstream structure, such as a drop inlet or manhole. Based on this interpretation of the criteria, 18” pipe has been deemed suitable for use in multiple locations in the project area including: downstream of proposed inlets and manholes in select locations, and as extensions of existing 18” culverts that are functioning properly.

The project scope does not include hydraulic modeling of the Carson River floodplain to determine impacts associated with any encroachments (fills) into the regulatory Floodway. As a result, the project will not cause encroachments that have any potential to reduce floodplain capacity. This limits the potential option of elevating the roadway profile in some locations, which would better define overtopping locations.

3.2 Roadway Adjustments

Roadway profile adjustments have been considered for purposes of improving drainage patterns.

Unfortunately, floodplain constraints limit some roadway profile adjustments that would have resulted in fill within floodplain limits. Roadway profile and cross section adjustments include:

August 2017 Final Hydraulics Report proposed DESIGN

Shift the high point from ~1129+00 to 1127+00 at the entrance to an existing parking area. This eliminates the need for the problematic cross culvert at the parking entrance in the roadside ditch, and deflects runoff to culverts north and south of this area.

Raise profile between 1160+00‐1165+00 and remove left side “berm” to allow overtopping flows to continue west to the river and not be confined on the roadway

Remove the “berm” in the roadway cross section along the west side of the road, between

1102+50 to 1104+00 to eliminate trapping of water and sedimentation on the roadway.

Create an uphill roadside ditch where possible, to convey runoff from adjacent hillslope runoff to existing and proposed culvert crossings.

Slope/super elevate the roadway surface towards the river so that any overtopping flows leave the road surface (instead of normal crown) at relatively shallow roadway longitudinal profiles areas including: 1087+00‐1098+50, 1103+50‐1110+00, 1147+50‐1149+00, 1154+00‐1158+50, 1164+00‐1172+00

To limit erosion on uphill ditches throughout the project area, curb and gutter will be constructed and tied in to the existing slope on the uphill side of the road. This design will limit erosion, and reduce the amount of sediment that ultimately reaches Carson River. The locations for curb and gutter were determined in conjunction with field observations and direction from the client.

3.3 Culvert Upgrades

Where feasible, culverts are upgraded to provide more capacity (up to standard of 25‐year) to limit overtopping of SVL. All culverts will be reinforced concrete pipe (RCP) to maximize capacity and sediment movement, except where existing corrugated metal pipe (CMP) culverts will be protected in place, and extended using additional CMP to accommodate the proposed roadway embankment. Culvert upgrades are limited in some locations due to steep uphill slopes, right of way limits, construction budget constraints, and visual impacts to property owners. Based on these limiting factors, each location for which a culvert is proposed was evaluated to determine the maximum, feasible culvert diameter. Based on this analysis, the maximum culvert size used on the project is 48” in diameter, which will be utilized at multiple locations throughout the project. Hydraulic calculations for the culverts were conducted using the computer program HY‐8, and the proposed culvert replacements, sizes, and capacities are summarized in Appendix E. If the existing culvert provides sufficient capacity (or is close), it has not been proposed for replacement.

It was recommended during preliminary design to utilize broken back culverts, particularly for larger sytstems, to discharge flow at the base of an embankment slope and allow for slower velocities at the outlet. However, per client direction, no broken back culverts with be utilized, and culverts will outlet directly on to the embankment slope with toewalls and riprap proposed to limit erosion.

3.4 Inlets

Due to steep uphill slopes or limited right of way, it may be difficult to excavate for a culvert entrance in certain locations.Where the drainage basin is relatively small and topographic constraints dictate, drop inlets are proposed. Most inlets are Type 5A (CFL standard detail). The inlet at 1175+00 is proposed as

August 2017 Final Hydraulics Report proposed DESIGN

Type 7B to accommodate a 36‐inch diameter pipe. Inlet capacity was determined with orifice calculations, accounting for loss of open area to the grates and debris (Appendix E).

There are two large basins that have an existing perforated standpipe/drop inlet configuration (design points 1174 and 1063). At these locations, the existing culvert systems are proposed to remain, and additional proposed culverts are to provide additional flow relief. The inlet grates at 1063 and 1174 will be upgraded to reduce clogging potential and maximize available culvert barrel capacity. This design takes advantage of the deep culverts beneath the roadway at these locations.

3.5 Spread Capacity

In areas of normal crown, flow within the roadside ditch or on the curb ad gutter was evaluated in 10‐yr conditions. In sump locations of normal crown, 50‐yr conditions were evaluated. Due to limited space in uphill ditches and flat longitudinal gradients, some locations violate spread criteria. However, the proposed design improves the existing condition and limits overtopping of SVL.

In areas of super elevated roadway, stormwater will flow off the pavement to the other side of the roadway towards the river and will not have spread or unacceptable depth. The general design intercepts most offsite water and conveys it beneath the roadway, so an abundance of pavement drainage is not anticipated.

For the purposes of calculations, spread and road side ditch capacities were analyzed using Bentley

FlowMaster. A section of curb and gutter or roadside ditch was created to mimic the proposed design, utilizing the minimum longitudinal grade, and the maximum approximate flow that a section of curb and gutter or roadside ditch will experience. Calculations were completed to show capacities (the maximum amount of flow that can be conveyed while obeying spread criteria), and the actual condition based on tributary flow. A summary table, along with all spread calculations are provided in Appendix E.

3.6 Summary of proposed design elements

A table summary of proposed culverts, capacities, and any 25‐year overtopping is included in Appendix E.

The drainage basin map is included in Appendix C.

Existing systems (culverts/inlets) to be removed and replaced/upgraded at:

1058+52 (upgraded inlet will connect to existing culvert, existing culvert will be protected in place) o Carson City requested that a standpipe outlet (similar to 1175+00 and 1063+00) be added to the 15” CMP located at 1058+50. The existing pipe is deep under the road, complicating the ability to upgrade size. To help with deposition of sediment outside of the small CMP pipe, a modified Type 5A inlet (CFL standard detail) is proposed, with an orifice hole. This will function similarly to the standpipe and orifice at 1063+00.

o Quantitative design guidance or criteria for a permanent sediment trap/basin BMP was researched with CFL, Carson City code, and State of Nevada. Nevada has a BMP guidance document (Best Management Practices Handbook (Reference 6) that addresses both temporary and permanent BMP design. The storage volume requirement is 0.5 inches of sediment per acre of drainage basin, which would result in 54,450 CF of volume at this site. Such an area is not available within the ROW and BIA disturbance area limitations.

August 2017 Final Hydraulics Report proposed DESIGN

The guidance provided for the orifice holes in a riser pipe are very small (1” dia) and are likely to clog with debris requiring frequent maintenance which is undesirable. A comparison with Denver area criteria using Water Quality Capture Volume (WQCV) as included in the Urban Drainage and Flood Control District Manual (Reference 7) was also evaluated. This volume would equate to approximately 0.2” of storage per acre drainage area and results in over 20,000 CF, which would also exceed available space.

Unfortunately, there is insufficient topographic data and scope/budget for a detailed pond design.

o As a result, the method chosen for design includes a single rectangular orifice, like at

1063+00, that provides for a similar reduction in peak flow. The 1063+00 standpipe (4’ above ground elevation, and 3’ below roadway overtopping) and orifice provides for a

63% reduction in peak flow that would otherwise pass through the culvert at the standpipe’s headwater elevation (17 CFS versus 46 CFS).

o At 1058+50, a 12”x6” hole will provide a similar reduction in peak with headwater at the top of its standpipe grate (4’ above ground elevation and 4.5’ below the roadway overtopping elevation). Calculations are in the appendix.

1118+97 (42” CMP to 48” RCP), 51 to 118 CFS capacity, less than 10‐yr, limited by available head

1145+43 (42” CMP to 48” RCP), 53 to 104 CFS capacity, less than 10‐yr, limited by available head

1175+15 (15” RCP to 36” RCP), 12 to 91 CFS capacity, less than 10‐yr, limited by available head o At the north end of the project area is an existing “pond” area with a 2’ tall standpipe perforated outlet in poor condition. The project goal was to increase flood capacity to the river below while still allowing some sediment deposition. At over 360 acres, the basin is too large for the sediment volume and drain time criteria listed above.

o The proposed design has five components that were considered an acceptable improvement within budgetary constraints.

1) Replace the standpipe outlet. The standpipe height is maintained (2’), but is lowered vertically to increase capacity during flood events. The new standpipe outlet will be a modification of a box inlet, with a vertical orifice pattern that matches the maximum release from the existing structure. The existing 18” CMP outlet will be maintained, as it is likely very deep (but its profile and alignment is not well known).

2) Install concrete apron around standpipe to facilitate sediment removal and contain ponded water

3) Install 36” flood relief culvert to increase overall capacity. The flood relief culvert engages once ponded water exceeds the elevation of the top of the standpipe to not interfere with the sediment settling function. The flood relief culvert is 36” and will be relatively shallow, draining down the slope towards the river. It passes through a type 7B Inlet (sized to accommodate the 36” pipe).

August 2017 Final Hydraulics Report proposed DESIGN

4) Raise the overall pond embankment height. Achieves greater capacity on standpipe outlet when in flood stages and allows adequate cover on the flood relief culvert.

5) Despite these improvements (which were a compromise of what was deemed practical and affordable), there remains 25‐year overtopping of the pond embankment and the river bank below. The riprap at these locations has been sized pursuant to HEC‐23 guidance for embankment overtopping.

Calculations are contained in the Appendix.

New systems (culverts/inlets) are proposed at these locations (see plans):

In some locations of concentrated offsite water flowing to SVL, where a culvert or inlet does not currently exist, new systems are proposed to be added. This will enable flow to exit the roadway surface as soon as possible. It is worth noting that as a result of adding new culverts, some drainage basins decreased which lead to other culverts not needing replacement.

1175+15 (addition of 36‐inch pipe) (upgrade from 12 to 306 CFS capacity, less than 10‐yr), limited by available head

1163+38 (addition of 30‐inch) (25‐yr)

1136+00 (24‐inch equivalent horizontal elliptical) (less than 10‐yr), limited by available head

1130+77 (right of alignment on tributary ‐ 18‐inch) (25‐yr)

1111+36 (24‐inch) (Less than 25‐yr), limited by available head on inlet

1108+95 (18‐inch) (25‐yr)

1107+40 (24‐inch) (less than 10‐yr), limited by available head on inlet

1103+55 (48‐inch) (less than 10‐yr), limited by available head and ROW o This location along SVL has a relatively large drainage basin and channel from upslope, however there are no culverts to drain beneath the roadway. In addition, this location is low and within the River floodplain and floodway. The roadway profile has multiple low points.

o The proposed design addresses the drainage situation as the priority and does not include a sediment collection facility that would increase drain time in this problematic area.

o A 48” culvert was deemed the maximum height that could reasonably fit within the vertical and horizontal constraints and budget. The design includes a headwall and wingwalls on the downstream end to better facilitate the rapid slope transition to tie to existing grades. A 3:1 sloping riprap apron is placed on this transition back to existing grade. The upstream end of the riprap apron has a concrete cutoff wall to lessen the risk of headcutting. The riprap has been sized according to HEC‐23 guidance for embankment overtopping considering its gradient. Some overtopping will remain in the 25‐year event, so riprap has also been sized on downslope side of the SVL embankment down to the river.

1101+43 (18‐inch) (25‐yr)

August 2017 Final Hydraulics Report proposed DESIGN

1062+83 (48” equivalent HERCP, increase to 119 CFS capacity, less than 10‐yr), limited by available head o There is an existing standpipe outlet at this location with an orifice. The outlet pipe is very deep. This structure will remain as is. There is a gully formed from erosion on the other side of SVL where overtopping flows have eroded the tall embankment.

o A flood relief culvert is provided to increase overall capacity. To not interfere with the sediment collection at the existing standpipe, the invert of this pipe has been set at a higher elevation, but still low enough to provide adequate cover. This culvert will discharge to a tall riprap rundown on the other side of SVL at the location of the present gully. Despite the additional flood culvert, there remains 25‐year overtopping. The riprap is designed per HEC‐23 guidance for embankment overtopping. Calculations are contained in the appendix.

3.7 Sediment Considerations

In general, pipes were oversized as much as possible to account for sedimentation, which maintains some capacity with less frequent maintenance required. In addition, RCP is proposed for all culvert replacements to facilitate water and sediment movement through the culverts. Extensions of existing

CMP pipe will be built at CMP. Where there is space, sediment collection areas will be created or enhanced on the upstream side of culverts or inlet structures in the form of depressions or larger standpipe outlets with perforations. These measures will facilitate future maintenance and sediment removal operations. Roadside ditches were configured to convey runoff from localized hillslope areas only, not convey large offsite channel water. This should lessen frequency of siltation in the ditches, and subsequent loss of capacity.

3.8 Streambank stabilization

Streambank stabilization along the Carson River is proposed in two locations as identified above. The streambank stabilization design has utilized measures that do not create fill within the Carson River floodplain and are a combination of riprap rock, erosion blanket, and natural vegetation/plantings

(willows) at the toe of the slope. Riparian vegetation will be seeded on the slopes. The measures will stabilize the grade under roadway overtopping conditions. An analysis of overtopping conditions and riprap design using guidance in Hydraulic Design Series No. 6 (Reference 5) is included in Appendix E. The planned drainage improvements and cross culvert upgrades will reduce the frequency of roadway overtopping to these areas.

August 2017 Final Hydraulics Report

CONCLUSIONS

4 CONCLUSIONS

The proposed design for drainage improvements along Sierra Vista Lane include upgrades to culverts and additional drop inlets to convey the 25‐year flood event where possible (the criteria). This will facilitate movement of runoff and sediment beneath the roadway, rather than on top of the roadway which as has led to road degradation and frequent maintenance needs. Additional inlets and culverts are proposed at locations that currently do not have a drainage feature, to limit reliance upon roadside ditches which are small (due to limited space) and fill with sediment. Roadway designs include super elevating the road surface towards the river and/or raising of the profile in select locations. Unfortunately, the Carson River regulatory floodplain will limit options that may have otherwise been considered.

5 REFERENCES

1. U.S. Department of Transportation, Federal Highway Administration, Federal Lands Highway (FLH)

Project Development and Design Manual (PDDM), Chapter 7 Hydrology and Hydraulics, 2011.

2. Carson City, NV, Municipal Code, Title 18 Appendix, Carson City Development Standards, Division 14

Storm Drainage, June 29, 2016.

3. Federal Emergency Management Agency, Flood Insurance Study for Carson City Nevada, February

19, 2014.

4. ERO Resources, Wetland Delineation Report (Draft), FHWA‐Sierra Vista Lane Improvement Project, Nevada FLAP 100 (1), Carson City Nevada. November 2016

5. Federal Highway Administration, HDS 6: River Engineering for Highway Encroachments, Highways in the River Environment. December 2001.

6. State of Nevada. Best Management Practices Handbook. October 2015.

7. Urban Drainage and Flood Control District. Urban Storm Drainage Criteria Manual, Volumes 1 and 2.

January, 2016.

August 2017 Final Hydraulics Report

Appendix A Criteria

Hydrologic Criteria

Federal Lands Highway

(FLH)

Carson City, NV Sierra Vista

Project - Applied Criteria PDDM

Carson City Development Standards

Rainfall

Depth N/A NOAA Atlas

14.2.1.2

NOAA Atlas

Design Frequency

Cross Drainage

Low-Standard road (Local Road) 25-year

Exhibit 7.1-A

25-year, 24-hour

Table 14.1 25-year

Check Flood Overtopping

Flood

Minimize channel flow over street (6” maximum depth)

14.2.1.4 Overtopping

flood

Floodplain encroachments 100-year 100-year, 24-hour Table 14.1 100-yr

Outlet Protection

For >/= 48” design flood

(25-yr) (reference:

HEC-14)

For <48” use detail C251-50

Outlet Velocity less than 5 fps:

rip-rap, Between 5 and 15 fps:

rip-rap and energy dissipater, Greater than

15 fps:

energy dissipater

14.3.3.3

25-year (48” and greater) Less than

48” = Standard

Detail C251-50

Headwater

Maximum HW/D = 1.5 for 48” or smaller;

HW/D = 1.2

larger than 48”.

Maximum HW < 5’ for

36” or smaller (no adverse impacts to adjacent properties);

HW/D = 1.5

larger than

36”.

14.3.5.4

Maximum

HW/D = 1.5

for 48” or smaller;

HW/D = 1.2

larger than

48”.

Minimum cross culvert size 24” N/A N/A 24”

Pavement Drainage

Capacity design (Low-Standard road, local road)

10-year. 50-yr in sump

Exhibit 7.1-A

5-year

Table 14.2

10-year. 50-yr in sump

Spread (Low-Standard road, local road)

On grade and sags: half of travel lane, not to exceed curb height.

Sumps and

Parking areas:

6” depth.

Flow contained in R/W, no curb overtopping, minimum 12’ wide dry lane centered.

10-yr: On grade and sags: half of travel lane, not to exceed curb height.

Sumps and

Parking areas: 6” depth (10yr).

12” in 100-yr

Ditches

Capacity Design 10-year

Exhibit 7.1-A

N/A N/A 10-year

Ditch Linings

Temporary:

2-year

Permanent:

10-year

Evaluate permissible velocity per

ASCE No. 77

14.3.6 10-year

Storm Drains

Capacity Design 10-year

(50-year in sumps)

7.3.4.2.1

5-year, 100-year in some exceptions (see Table

14.2)

Table 14.2 10-year

(50-year in sumps)

Minimum pipe size 15” 15” 14.3.2.4 10-year

(50-year in sumps)

Hydrologic Procedure Selection

Un-gaged Watershed Peak Flow Methods

Based on drainage area (DA)

DA < 200

acres: Rational

Method

DA > 200

acres: NRCS

TR 55 or Regression Equations

7.2.4.3

DA < 100

acres:

Rational Method, NRCS TR 55 or NRCS UH

10 mi2 > DA >

100 acres:

NRCS TR 55

or NRCS UH

DA > 10 mi2 :

NRCS UH

14.2.1.1

DA < 100

acres:

Rational Method, NRCS TR

55 or NRCS

UH

10 mi2 > DA > 100 acres:

NRCS TR

55 or NRCS

UH

DA > 10 mi2

: NRCS UH

Gaged Watershed Peak Flow Methods

Minimum 10-year period of record Flood

Frequency Analysis

7.2.4.3 N/A N/A

Flood

Frequency Analysis

Appendix B Existing Conditions photos, Floodplain Information, Water Quality for Carson River

Sierra Vista Lane Existing Conditions photographs (taken 9/2015)

Standpipe culvert inlet at Mile 0.18 / Sta. 1174 Culvert exit at river at Mile 0.18 / Sta. 1174

Surface overflow path from mile 0.18 / sta. 1174 into river Mile 0.32 / Sta. 1165, culvert outlet to river

Mile 0.32 / Sta 1165 looking upstream at basin Mile 0.39 / Sta 1160 culvert entrance, sediment accumulation

Mile 0.72 / Sta 1145 culvert entrance Mile 0.72 / Sta 1145 culvert exit

Mile 0.95 / Sta. 1130 looking upstream Mile 1.07 / Sta 1126(a), side drain at parking lot entrance

Mile 1.22 / Sta 1118 culvert entrance Mile 1.22 / Sta 1118 culvert exit

Mile 1.33 / Sta. 1111 looking south Mile 1.33 / Sta 1111 overflow path/erosion to river

Mile 1.37 / Sta 1108 looking south

Mile 1.37 / Sta 1107 road low point, overflows to river/erosion

Mile 1.37 / Sta 1108 overflows into river and erosion

Mile 1.52 / Sta 1104-1103 roadway low point. Looking upstream at offsite basin Mile 1.52 / Sta 1104-1103 overflows into river/sedimentation

Sta 1109-1104 overtopping erosion of streambank Sta 1109-1104 overtopping erosion of streambank and existing riprap

Mile 1.52+ / Sta 1099 rills on uphill slope

Mile 2.28 / Sta 1063 drop inlet

Mile 2.28 / Sta 1063 looking upstream/sedimentation Mile 2.28 / Sta 1063 looking downstream

Mile 2.36 / Sta 1058 culvert entrance Mile 2.36 / Sta 1058 looking downstream

CARSON CITY,

NEVADA

INDEPENDENT CITY

COMMUNITY NAME COMMUNITY NUMBER

CARSON CITY, CITY OF 320001

REVISED: FEBRUARY 19, 2014

Federal Emergency Management Agency

FLOOD INSURANCE STUDY NUMBER

320001V000B

Carson City

CROSS SECTION DISTANCE

1 WIDTH (FEET)

SECTION

AREA

(SQUARE

FEET)

MEAN

VELOCITY

(FEET PER

SECOND)

REGULATORY

WITHOUT

FLOODWAY

WITH

FLOODWAY

INCREASE

Carson River

A 0 266 2,763 13.0 4,583.2 4,583.2 4,584.2 1.0

B 1,140 162 1,921 18.7 4,590.5 4,590.5 4,590.6 0.1

C 2,845 144 2,195 16.4 4,598.8 4,598.8 4,598.8 0.0

D 4,045 170 3,441 10.5 4,603.3 4,603.3 4,603.4 0.1

E 4,455 340 5,987 6.0 4,604.2 4,604.2 4,604.9 0.7

F 4,565 225 5,235 6.9 4,604.3 4,604.3 4,605.0 0.7

G 4,645 275 7,460 4.8 4,604.8 4,604.8 4,605.3 0.5

H 5,005 700 13,135 2.7 4,605.1 4,605.1 4,605.7 0.6

I 6,185 500 8,876 4.1 4,605.1 4,605.1 4,605.7 0.6

J 7,225 960 16,469 2.2 4,605.2 4,605.2 4,606.0 0.8

K 10,375 2,501 37,726 1.0 4,605.4 4,605.4 4,606.2 0.8

L 11,475 2,765 37,158 1.0 4,605.4 4,605.4 4,606.2 0.8

M 13,195 2,342 28,053 1.3 4,605.4 4,605.4 4,606.2 0.8

N 14,835 1,215 13,130 2.7 4,605.4 4,605.4 4,606.2 0.8

O 16,680 1,253 11,609 3.1 4,605.7 4,605.7 4,606.5 0.8

P 18,060 1,361 10,623 3.4 4,606.1 4,606.1 4,607.0 0.9

FLOODING SOURCE FLOODWAY

1-PERCENT-ANNUAL-CHANCE FLOOD

WATER-SURFACE ELEVATION (FEET NAVD)

8,060 ,36 0,6 3 3 ,606 ,606 ,60 0 0 9

Q 19,620 3,380 20,277 1.8 4,606.5 4,606.5 4,607.4 0.9

R 20,760 3,404 18,706 1.9 4,606.7 4,606.7 4,607.6 0.9

S 21,990 3,208 14,848 2.4 4,606.9 4,606.9 4,607.8 0.9

T 23,410 2,186 6,035 6.0 4,608.3 4,608.3 4,608.6 0.3

U 24,575 1,212 5,671 6.3 4,610.7 4,610.7 4,611.0 0.3

V 25,020 1,104 3,756 9.1 4,612.8 4,612.8 4,612.8 0.0

W 25,050 1,050 3,665 9.8 4,612.8 4,612.8 4,612.8 0.0

X 26,815 445 4,814 7.5 4,616.2 4,616.2 4,617.0 0.8

Y 28,845 185 2,449 14.7 4,618.2 4,618.2 4,618.8 0.6

Z 30,380 180 2,995 12.0 4,622.1 4,622.1 4,623.1 1.0

AA 32,130 188 2,427 14.8 4,625.5 4,625.5 4,626.5 1.0

Feet Above Downstream Limit of Detailed Study (Located 150 Feet Downstream of Brunswick Canyon Road)

FEDERAL EMERGENCY MANAGEMENT AGENCY

CARSON CITY, NEVADA

INDEPENDENT CITY

FLOODWAY DATA

CARSON RIVER

TABLE X

TABLE 10

TABLE X

TABLE 10

TABLE X

TABLE 10

TABLE X

TABLE 3

TABLE X

TABLE 10

TABLE X

TABLE 10

TABLE X

TABLE 9

Attachment 4 – Category 5 Waters (303(d) List) Nevada 2012 Integrated Report

Waterbody ID WQS Water Name Description Parameter New ListingSize HYDROGRAPHIC REGION/BASIN Carson River Basin a b dImpaired Use(s) c

NV08-CR-09_00 1816 Carson River From Mexican Ditch Gage to New Empire7 M

Escherichia coli YesRWC

Mercury in Fish Tissue FC

Oxygen, Dissolved AQL

Temperature, water AQL

NV08-CR-10_00 1818 Carson River From New Empire to Dayton Bridge10.4 M

Mercury in Fish Tissue FC

Mercury in Sediment AQL

NV08-CR-11_00 1822 Carson River From Dayton Bridge to Weeks Bridge at Highway 9525.8 M

Mercury in Fish Tissue FC

Mercury in Sediment AQL

Mercury in Water Column MDS

NV08-CR-12_00 1824 Carson River From Weeks Bridge at Highway 95 to Lahontan Reservoir6.3 M

Mercury in Fish Tissue FC

Mercury in Sediment AQL

NV08-CR-06_02 1808 Carson River, East and West Forks and Carson River

Carson River, East Fork from Muller Lane to the West Fork, Carson River, West Fork from Muller Lane to the East Fork, and Carson River from the confluence of the East and West Forks to Genoa Lane

4.3 M

Temperature, water AQL

NV08-CR-03_00 1802 Carson River, East Fork At the Nevada-California state line0 M

Temperature, water AQL

Total Suspended Solids (TSS) AQL

Turbidity AQL

NV08-CR-04_00 1804 Carson River, East Fork From Nevada-California state line to Riverview Mobile Home Park9.2 M

Temperature, water AQL

NV08-CR-05_01 1806 Carson River, East Fork From Riverview Mobile Home Park to Highway 886.5 M

Temperature, water AQL

NV08-CR-13-C_00 1826 Carson River, Lower From Lahontan Reservoir to Carson Sink (the natural channel)44 M

Escherichia coli RWC

Iron AQL

Manganese IRR

Mercury in Fish Tissue FC

Mercury in Sediment AQL

Total Dissolved Solids YesMDS

Attachment 4 – Category 5 Waters (303(d) List) - Page 16 of 24

b. M = Mile(s), A = Acre(s)

a. WQS references the section in Chapter 445A of the Nevada Administrative Code that contains the water quality standards.

d. If the New Listing column is Yes, then the parameter is a new listing for 2012; if column is blank, then the parameter was on the 2008-10 list

c. AQL = Aquatic Life, EWQ = Enhancement of Water Quality, FC = Fish Consumption, IND = Industrial Supply, IRR = Irrigation, MDS = Municipal Domestic Supply, PWL = Propagation of Wildlife, RNC = Recreation Not Involving Contact with Water, RWC = Recreation Involving Contact with Water, WLS = Watering of Livestock apowers Highlight

Appendix C Hydrologic Computations, Basin Map

Existing Condition at Design Points

Basin/Design Pt ID Design Point ID (MP distance from North, see Scope)

Roadway Station

Basin Area (sqft)

Basin Area (acre) Existing Pipe Size Ex. Pipe Material 10‐Year Flow 25‐Year Flow

50‐Year Flow

100‐Year Flow

Ex Culvert Capacity

Ex Inlet capacity (if applicable)

Adjacent Land Owner (Upstream) Hydrologic method

1174A (road ditch) 0.18 gets overflow from 1174, and local 15" w/ drop inlet RCP 8.0 City 1174 0.18 1172+30.86 15865228 364.2 18" w/ drop inlet CMP 323.2 408.1 477.6 550.0 18.0 12 (orifice) City SCS 1165 0.32 1165+48.05 2816853 64.7 24" CMP 33.8 49.4 65.9 87.1 15.9 ‐‐ City Rational 1160 0.39 1160+26.39 636192 14.6 18" CMP 9.4 13.2 17.0 23.5 8.2 ‐‐ City Rational 1145 0.72 1145+36.89 10353092 237.7 42" CMP 219.0 277.6 325.8 376.2 33.1 ‐‐ City SCS 1130 0.95 1130+72.34 3849434 88.4 18" CMP 44.0 63.4 87.3 116.0 9.3 ‐‐ City Rational

1126A (road ditch) 1.07 1127+62.07 513231 11.8 18" CMP 7.1 9.9 13.0 17.9 2.6 ‐‐ City Rational 1126 1.07 1126+01.94 400437 9.2 18" CMP 5.5 7.6 9.7 13.7 8.6 ‐‐ City Rational 1118 1.22 1118+91.14 8824412 202.6 42" CMP 176.0 225.3 266.2 309.3 51.0 ‐‐ BLM SCS 1111 1.33 1111+17.98 582086 13.4 N/A N/A 7.7 11.1 15.2 20.2 N/A ‐‐ BLM Rational 1108 1.37 1108+90.29 225296 5.2 N/A N/A 4.9 5.7 9.5 12.6 N/A ‐‐ Private Rational 1107 new 1107+43.49 1192767 27.4 N/A N/A 14.3 20.9 29.3 38.2 N/A ‐‐ Private Rational 1104 1.52 1104+72.61 17155876 393.8 N/A N/A 231.6 298.1 353.8 412.9 N/A ‐‐ Private SCS 1099 new 1099+ 277769 6.4 N/A N/A 3.9 5.4 7.2 9.9 N/A ‐‐ Private Rational 1063 2.28 1063+07.97 17357308 398.5 24" w/ drop inlet CMP 233.0 300.6 358.5 420.6 48.4 21 (orifice) BLM SCS 1058 2.36 1058+54.45 1306354 30.0 15" CMP 15.3 20.3 24.9 36.4 16.1 ‐‐ BLM Rational

N/A = no culvert present (orifice)= orifice control on inlet capacity

12/1/2016 Precipitation Frequency Data Server http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_printpage.html?lat=39.1869&lon=119.7125&data=intensity&units=english&series=pds#curves 1/6

NOAA Atlas 14, Volume 1, Version 5 Location name: Carson City, Nevada, USA* Latitude: 39.1869°, Longitude: 119.7125°

Elevation: 4626.15 ft**

* source: ESRI Maps ** source: USGS

POINT PRECIPITATION FREQUENCY ESTIMATES

Sanja Perica, Sarah Dietz, Sarah Heim, Lillian Hiner, Kazungu Maitaria, Deborah Martin, Sandra Pavlovic, Ishani Roy, Carl Trypaluk, Dale Unruh, Fenglin Yan, Michael Yekta, Tan Zhao, Geoffrey

Bonnin, Daniel Brewer, LiChuan Chen, Tye Parzybok, John Yarchoan

NOAA, National Weather Service, Silver Spring,…