Hydrologic-Hidraulic Analysis Report - AC-830579.pdf

HYDROLOGIC-HIDRAULIC ANALYSIS

MAIN DRAINAGE STRUCTURES

LANDSLIDES AND ROAD DAMAGE PROJECT

AC-8095444, GROUP B, ROAD PR-124

LARES, PUERTO RICO

JOSE A. BATLLE & ASSOCIATES

September 2021

Hydrologic – Hydraulic Analysis September 2021

Landslides and Road Damage Project AC-809544

Lares, Puerto Rico

1. HYDROLOGY

1.1 Methodology

An Intensity-Duration-Frequency relationship was developed for each area of interest and obtained for the 25-year, 50-year and 100-year frequency rainfall events. The rainfall data were obtained from the National Weather Service NOAA Atlas 14 publication. The peak flows for the selected rainfall frequencies were computed using the Rational Method.

According to Chapter 11 of the Puerto Rico Highway and Transportation Authority (PRHTA)

Design Manual, the Rational Method is recommended and commonly used in the design of storm drainage features with associated basin areas up 200 acres. The Rational Method is expressed as:

Q = CIA

where, Q = peak flow in cfs

C = Runoff coefficient

I = rainfall intensity in inches/hr in which the rainfall duration equals the time of concentration of the basin

A = Drainage basin area in acres

For this analysis, a value of C=0.45 was used for the existing drainage areas associated with lateral drainage channels, existing and main road crossings to be improved, consisting of rural areas with dense vegetation and steep slopes, while C=0.90 was used to estimate peak flows to design lateral road ditches and other drainage features.

1.2 Summary of Hydrologic Parameters and Computed Peak Flows

I (in/hr)

ID Site A (acres) C tc (min) 25-yr 50-yr 100-yr

ER-HWY-105 2.36 0.45 5 10.4 11.2 12.1

ER-HWY-106 2.90 0.45 5 9.73 10.4 11.1

ER-HWY-108 3.48 0.45 5 9.73 10.4 11.1

A summary of hydrologic parameters computations, rainfall data from NOAA Atlas 14 publication, location of evaluated sites and delineation of drainage areas are included as

Attachment 1.

Computed Peak Flows

Once hydrologic parameters for the rational formula being established then computation of peak flows where estimated as shown in the following Table.

ID Site Q25 (cfs) Q50 (cfs) Q100 (cfs)

ER-HWY-105 11.0 11.9 12.8

ER-HWY-106 12.7 13.6 14.5

ER-HWY-108 15.2 16.3 17.4

2. HYDRAULIC EVALUATION

2.1 Methodology – Road Crossings

Once peak discharges are computed for the selected storm vents (25 and 100-year) then the existing drainage crossings are evaluated to determine if they have the capacity to convey the computed discharges. In addition, the size and geometry of the new road crossings (pipe culverts) were also evaluated. The required culverts were evaluated using the methodology established by the Federal

Highway Administration (FHWA). The analyses were performed using the FHWA computer program HY-8, version 7.30. This program uses the equations and nomographs developed by the

FWA por the analysis and design of circular, elliptical and rectangular culverts, considering different factors such as the inlet and outlet control conditions and road/embankment characteristics.

The following information was provided for each culvert:

• Geometry (circular on most of the cases)

• Material

• Manning’s roughness coefficient (“n’)

• Entrance type

• Length of culvert

• Invert Elevation (I.E.)

• Outlet Elevation (O.E.)

• Elevation (minimum) of road (Top of Road)

• Downstream water elevation (tailwater elevation)

• Longitudinal slope of culvert

Summary of Resulting Structures

The resulting culverts are summarized as follows:

ID Area/HW# Area (acres) 25-yr Q (cfs) 100-yr Q Culvert size

ER-HWY-105 (existing) 2.36 11.0 12.8 1-30” RCP

ER-HWY-106 (existing) 2.90 12.7 14.5 1-30” RCP

ER-HWY-108 (existing) 3.48 15.2 17.4 1-30” RCP

The culvert analysis summary tables using HY-8 computer program are included as Attachment 2.

The HY-8 program was also used to determine critical and normal flow depths within the recommended storm pipes to define some erosion protection (such as riprap aprons) to be located at the discharge points.

2.2 Methodology –Lateral Drainage Channels

Lateral drainage channels (waterways) are recommended to collect and manage the incoming runoff from the previously discussed drainage areas. The lateral drainage channels along the opposite road shoulder or edge were evaluated considering the drainage area consisting of the half of the road width plus the width of the proposed retaining walls, where applied. The drainage areas considering only these conditions produce non-significant peak flows when compared with the previously mentioned drainage basins considered for road crossings and discharge pipes. A value of C=0.9 was considered for paved road segments.

For the lateral drainage channels to collect the peak discharges computed in Section 1.2 of this document the analyses were performed using the Manning’s Formula.

Q = (1.486/n) A R 2/3 S ½

Various drainage channels or waterways sections were defined based on field conditions and recommended according to the computed peak flows. The recommended channel sections will be concrete covered with an assumed “n” value of 0.013. The final capacity of the recommended waterways depends on the longitudinal slope of each road segment. The maximum discharge flows for each recommended lateral channel are:

Type Side slope Side slope Base Depth Top Width Road Slope Capacity

(left) (right) (m) (m) (m) (m/m) (cfs)

I 3:1 3:1 0 0.15 0.90 0.080 9.6

II 0.6:1 3.5:1 0 0.30 1.2 0.080 4.9

IV 3:1 1:1 0.30 0.30 1.5 0.080 69.0

V 3:1 1:1 0.30 0.20 1.1 0.080 27.8

VI 3:1 1:1 0.30 0.45 1.2 0.080 116.1

A longitudinal slope of 0.080 was assumed for these analyses. Any variation of the slope will change the selection of the adequate lateral drainage channel.

For the lateral drainage channels for the opposite edge of Road PR-124 the estimated peak flows are one (1) cfs or less (for each 100 meters of road length). Type I or II lateral drainage channels or a system of curb and gutter are recommended for these cases. Examples of hydraulic computations regarding recommended drainage channels are included as Attachment 3 of this report.

The lateral drainage channels at sites ER-HWY-105, ER-HWY-106 and ER-HWY-108 discharges into proposed inlets, where RCP discharges eventually into the existing pipes discharging into lateral embankments. The existing pipes consist of 30-inches RCP’s. Adequate erosion protection measurements (riprap aprons) are recommended at the exit of drainage pipes.

The following waterways or lateral drainage channels are recommended for the analyzed areas:

ID Area 25-yr Q(cfs) 100-yr Q Drainage Channel Type

ER-HWY-105 11.0 12.8 Type V

ER-HWY-106 12.7 14.5 Type V

ER-HWY-108 15.2 17.4 Type V

3. EROSION PROTECTION

The installation of erosion control measures such as grouted rip rap aprons are recommended at the exit of the proposed storm pipes and existing crossings. Based upon a preliminary evaluation the rip rap stones are recommended for the sites due to the outfall velocities from the pipe. The riprap should have a minimum size (D50) of ten inches according to the available references such as the

FHWA HEC 14 manual. This manual establishes guidelines for the installation of rip rap apron at the exit of pipes or culverts less than 60 inches in diameter (Chapter 10.2 of HEC 14 manual). The exit flows from pipes or culverts discharges into road embankments under very steep slope conditions. The HEC 14 manual does not consider the installation of aprons for steep and very steep slope conditions such as the conditions presented in this project. A typical riprap apron structure is recommended to be installed at the pipes discharge points, where the conditions allow this type of construction. Other erosion control alternatives such as the use of Vetiver plants should be considered there the topographic conditions do not permit the installation of riprap aprons.

4. RECOMMENDATIONS

A proper cleaning and maintenance program must be established for all drainage features of the road segments under evaluation and adjacent areas and immediate drainage elements that could impact the evaluated sites.

ATTACHMENT 1

HYDROLOGIC PARAMETERS COMPUTATIONS

DELINEATION OF DRAINAGE AREAS – GROUP B

RAINFALL DATA FROM NOAA ATLAS 14

AC - 8095444

José A. Batlle & Asociados, CSP APPENDIX -

GROUP “B”

SITES: 105, 106 & 108

LANDSLIDE AND ROAD DAMAGE

EVALUATION AND REPAIR RECOMMENDATIONS

AC-830579 DATE: August 31, 2021

Location & Delineation of Drainage Areas Site ER-HWY-105

A

ER-HWY-105

José A. Batlle & Asociados, CSP APPENDIX -

GROUP “B”

SITES: 105, 106 & 108

LANDSLIDE AND ROAD DAMAGE

EVALUATION AND REPAIR RECOMMENDATIONS

AC-830579 DATE: August 31, 2021

Location & Delineation of Drainage Areas Site ER-HWY-106 & 108

A

ER-HWY-106

ER-HWY-108

Group Municipality Road ID Site Station ID Tc Imin) C

(sq m) (acres) 25-Year 50-Year 50-Year 25-Year 50-Year 100-Year B Lares PR-124 105 ER-HWY-105 9557.5 2.36 5 0.45 10.4 11.2 12.1 11.05 11.90 12.85

B Lares PR-124 106 ER-HWY-106 11748.1 2.90 5 0.45 9.73 10.4 11.1 12.70 13.58 14.49

B Lares PR-124 108 ER-HWY-108 14088 3.48 5 0.45 9.73 10.4 11.1 15.23 16.28 17.38

Time of concentration

Kirpich - tc=0.0078xL^0.77XS^-0.385

ID L(m) L(ft) H1(m) H2(m) H1-H2(m) H1-H2(ft) S tc(min)

105 110 361 290 225 65 213.2 0.591 0.88952

106 145 476 380 350 30 98.4 0.207 1.64818

108 150 492 510 450 60 196.8 0.4 1.31255

For tc values less than 5 minutes, use tc = 5 min

I (in/hr) Qpeak (cfs)Drainage Area

ATTACHMENT 2

SUMMARY TABLE OF HYDRAULIC ANALYSIS RESULTS

HY-8 PROGRAM COMPUTER PRINTOUTS (GROUP B)

AC – 8095444

HY-8 Analysis Results

Culvert Summary Table - Culvert 2

Culvert Crossing: ER-HWY-105

Total Dischar ge (cfs)

Culvert Dischar ge (cfs)

Headwa ter Elevatio n (ft)

Inlet Control Depth(ft)

Outlet Control Depth(ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwate r Depth (ft)

Outlet Velocity (ft/s)

Tailwate r Velocity (ft/s)

11.00 11.00 730.97 1.10 0.0* 1-S2n 0.34 1.11 0.40 0.22 21.04 7.93

11.30 11.30 730.99 1.12 0.0* 1-S2n 0.34 1.13 0.41 0.22 21.09 8.01

11.60 11.60 731.01 1.14 0.0* 1-S2n 0.35 1.14 0.42 0.22 21.30 8.09

11.90 11.90 731.03 1.16 0.0* 1-S2n 0.35 1.16 0.42 0.23 21.65 8.16

12.20 12.20 731.05 1.18 0.0* 1-S2n 0.36 1.17 0.42 0.23 22.02 8.24

12.50 12.50 731.07 1.20 0.0* 1-S2n 0.36 1.19 0.43 0.23 21.85 8.31

12.80 12.80 731.09 1.22 0.0* 1-S2n 0.37 1.20 0.44 0.24 21.85 8.38

13.10 13.10 731.10 1.23 0.0* 1-S2n 0.37 1.22 0.45 0.24 21.98 8.45

13.40 13.40 731.12 1.25 0.0* 1-S2n 0.38 1.23 0.45 0.24 22.20 8.52

13.70 13.70 731.14 1.27 0.0* 1-S2n 0.38 1.25 0.45 0.25 22.50 8.59

14.00 14.00 731.16 1.29 0.0* 1-S2n 0.39 1.26 0.46 0.25 22.73 8.66

Culvert Summary Table - Culvert 3

Culvert Crossing: ER-HWY-106

Total Dischar ge (cfs)

Culvert Dischar ge (cfs)

Headwa ter Elevatio n (ft)

Inlet Control Depth(ft)

Outlet Control Depth(ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwate r Depth (ft)

Outlet Velocity (ft/s)

Tailwate r Velocity (ft/s)

12.70 12.70 1147.14 1.21 0.0* 1-S2n 0.44 1.20 0.50 0.23 18.61 8.17

13.03 13.03 1147.16 1.23 0.0* 1-S2n 0.45 1.21 0.51 0.24 18.03 8.24

13.36 13.36 1147.18 1.25 0.0* 1-S2n 0.45 1.23 0.52 0.24 18.00 8.32

13.69 13.69 1147.20 1.27 0.0* 1-S2n 0.46 1.25 0.53 0.24 18.04 8.39

14.02 14.02 1147.22 1.29 0.0* 1-S2n 0.46 1.26 0.53 0.25 18.14 8.46

14.35 14.35 1147.24 1.31 0.0* 1-S2n 0.47 1.28 0.54 0.25 18.30 8.53

14.50 14.50 1147.25 1.32 0.0* 1-S2n 0.47 1.28 0.54 0.25 18.38 8.56

15.01 15.01 1147.28 1.35 0.0* 1-S2n 0.48 1.30 0.55 0.26 18.48 8.66

15.34 15.34 1147.30 1.37 0.0* 1-S2n 0.48 1.32 0.56 0.26 18.45 8.73

15.67 15.67 1147.32 1.39 0.0* 1-S2n 0.49 1.33 0.57 0.26 18.47 8.80

16.00 16.00 1147.34 1.41 0.0* 1-S2n 0.49 1.35 0.58 0.27 18.54 8.86

Culvert Summary Table - Culvert 4

Culvert Crossing: ER-HWY-108

Total Dischar ge (cfs)

Culvert Dischar ge (cfs)

Headwa ter Elevatio n (ft)

Inlet Control Depth(ft)

Outlet Control Depth(ft)

Flow Type

Normal Depth (ft)

Critical Depth (ft)

Outlet Depth (ft)

Tailwate r Depth (ft)

Outlet Velocity (ft/s)

Tailwate r Velocity (ft/s)

15.20 15.20 1485.59 1.36 0.0* 1-S2n 0.52 1.31 0.58 0.29 17.58 7.84

15.48 15.48 1485.61 1.38 0.0* 1-S2n 0.52 1.33 0.58 0.30 17.76 7.89

15.76 15.76 1485.63 1.40 0.0* 1-S2n 0.53 1.34 0.59 0.30 17.81 7.94

16.04 16.04 1485.64 1.41 0.0* 1-S2n 0.53 1.35 0.59 0.30 17.77 7.99

16.32 16.32 1485.66 1.43 0.0* 1-S2n 0.54 1.36 0.60 0.31 17.77 8.04

16.60 16.60 1485.68 1.45 0.0* 1-S2n 0.54 1.37 0.61 0.31 17.80 8.09

16.88 16.88 1485.69 1.46 0.0* 1-S2n 0.55 1.38 0.62 0.31 17.86 8.13

17.16 17.16 1485.71 1.48 0.0* 1-S2n 0.55 1.40 0.62 0.32 17.95 8.18

17.40 17.40 1485.72 1.49 0.0* 1-S2n 0.55 1.41 0.62 0.32 18.08 8.22

17.72 17.72 1485.74 1.51 0.0* 1-S2n 0.56 1.42 0.63 0.32 18.23 8.27

18.00 18.00 1485.76 1.53 0.0* 1-S2n 0.56 1.43 0.63 0.33 18.33 8.32

ATTACHMENT 3

HYDRAULIC COMPUTATIONS

LATERAL DRAINAGE CHANNELS – GROUP B

AC - 8095444

HYDRAULIC COMPUTATIONS USING MANNING'S FORMULA

Lateral channels for roads

Channel Depth (ft) Base (ft) Left Side S (H:V) Right Side slope (H:V)W Perimeter (ft) T width (ft) Area (ft2) Hydraulic Slope manning's nvelocity Q (cfs)

Type Radius (ft) (ft/ft) (ft/s)

I 0.50 0.00 3.00 3.00 3.00 3.00 0.75 0.25 0.080 0.013 12.83 9.62

II 1.00 0.00 0.57 3.50 4.07 4.07 0.57 0.14 0.080 0.013 8.69 4.92

IV 1.00 1.00 3.00 1.00 5.00 5.00 3.00 0.60 0.080 0.013 23.00 69.00

IV-A 1.30 1.00 3.00 1.00 6.20 6.20 4.68 0.75 0.080 0.013 26.80 125.44

V 0.66 1.00 3.00 1.00 3.64 3.64 1.53 0.42 0.080 0.013 18.15 27.79

VI 1.50 1.00 1.00 1.00 4.00 4.00 3.75 0.94 0.080 0.013 30.97 116.14