Hydrologic-Hidraulic Analysis Report - AC-831579.pdf

HYDROLOGIC-HIDRAULIC ANALYSIS

MAIN DRINAGE STRUCTURES

LANDSLIDES AND ROAD DAMAGE PROJECT

AC-8095444, GROUP C, ROADS PR-128, PR-112 and PR-1 LARES, MOCA and SAN JUAN, PUERTO RICO

JOSE A. BATLLE & ASSOCIATES

October 2019

Hydrologic – Hydraulic Analysis October 2019

Landslides and Road Damage Project AC-809544

Lares, Moca and San Juan, Puerto Rico

1. HYDROLOGY

1.1 Methodology

An Intensity-Duration-Frequency relationship was developed for each area of interest was 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 the Highway 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=0.0.45 was used for the existing drainage areas associated with existing and proposed main road crossings consisting of rural areas with dense vegetation and steep slopes, and 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-133 10.30 0.45 5 10.2 10.9 11.7

ER-HWY-134 9.58 0.45 5 10.2 10.9 11.7

ER-HWY-135 9.77 0.45 5 10.2 10.9 11.7

ER-HWY-136 3.35 0.45 5 10.2 10.9 11.7

ER-HWY-137 5.98 0.45 5 10.2 10.9 11.7

ER-HWY-138 5.10 0.45 5 10.2 10.9 11.7

ER-HWY-139 3.91 0.45 5 10.2 10.9 11.7

ER-HWY-139B 2.87 0.45 5 10.2 10.9 11.7

ER-HWY-140 2.90 0.45 5 10.2 10.9 11.7

ER-HWY-60 3.71 0.45 5 10.1 10.7 11.4

ER-HWY-04* Not defined 8.54 9.28 9.97

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-133 47.3 50.5 54.2

ER-HWY-134 25.6 27.4 29.4

ER-HWY-135 44.8 47.9 51.4

ER-HWY-136 15.4 16.4 17.6

ER-HWY-137 27.5 29.4 31.5

ER-HWY-138 23.4 25.0 26.8

ER-HWY-139 17.9 19.2 20.6

ER-HWY-139B 13.2 14.1 15.1

ER-HWY-140 17.0 18.2 19.5

ER-HWY-60 7.8 8.3 8.8

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-133 (new) 10.30 47.3 54.2 1-36” RCP

ER-HWY-134 (new) 5.58 25.6 29.4 1-30” RCP

ER-HWY-135+136 (existing) 13.12 60.2 69.1 1.90 m X 1.09 m BC

ER-HWY-137 (new) 5.98 27.5 31.5 1-30” RCP

ER-HWY-138 (new) 5.10 23.4 26.8 1-30” RCP

ER-HWY-139+139B (existing) 6.77 31.1 35.7 1-30” RCP

ER-HWY-140 (new) 3.71 11.7 19.5 1-30” RCP

The summarized printout tables from the HY-8 program are included with this report. No culvert crossings are required for sites ER-HWY-04 and ER-HWY-60.

2.2 Methodology –Lateral Drainage Channels

Lateral drainage channels were 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. A value of C=0.9 was considered for these cases.

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 channel sections were defined based of 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 lateral drainage channels depends of the longitudinal slope of each road segment (S=0.100 assumed for the following examples). The maximum discharge flow 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 0.062 8.47

I I 0.6:1 3.5:1 0 0.30 1.25 0.062 4.34

I I I 0 0 0.45 0.30 0.45 0.062 56.92

I V 3:1 1:1 0.30 0.30 1.5 0.062 98.11

V 3:1 1:1 0.30 0.20 1.2 0.062 37.14

VI 3:1 1:1 0.30 0.20 1.1 0.062 63.48

VII 3:1 0 0.30 0.20 1.1 0.062 113.85

For the lateral drainage channels for the opposite edge of Road PR-128 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.

3. RECOMMENDATIONS

The installation of erosion control measures such as rip rap are recommended at the entrance and exit of the proposed and existing crossings. 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