Land & Watersheds

Water Resources Engineering · Puerto Rico

Rural & Fluvial Hydrology & Hydraulics

Hydrologic & Hydraulic Study Report

River, Floodplain & Culvert; [Project Name & Location]

Prepared for

[Client / Owner]

[Company / Municipality]

Prepared by

David Vagnetti, PE

Land & Watersheds

Date · Project No.

[Month YYYY]

No. [LW-0000] · Rev. [0]

GEOHEC-HMS / RAS 2D FEMA FIRM / BFE SIGNED & SEALED

Land & Watersheds

Rural / Fluvial H&H · Report

Land & Watersheds · [Project No.] [Project Name]

·Contents

Table of contents.

1 · Introduction[p]

1.1 Project description & location[p]

1.2 Scope & purpose[p]

1.3 Methodology & data sources[p]

1.4 Authorization & study area[p]

2 · Watershed characterization (GIS)[p]

3 · Hydrology[p]

3.1 Rainfall, NOAA Atlas 14[p]

3.2 Watershed modeling, GEOHEC-HMS[p]

4 · Hydraulics[p]

4.1 River hydraulics & BFE, RAS 2D[p]

4.2 Culvert / bridge & scour protection[p]

5 · Results & flood mapping[p]

6 · Observations & conclusions[p]

Certification[p]

List of Tables

Table 2-1 Watershed parameters
Table 3-1 NOAA Atlas 14 rainfall depths
Table 3-2 HEC-HMS peak discharges
Table 4-1 HEC-RAS WSEL / BFE

List of Figures

Fig 1 Effective FIRM & BFE
Fig 2 NOAA Atlas 14 PF estimates
Fig 3 GIS watershed delineation
Fig 4 HEC-RAS 2D mesh / WSEL
Fig 5 Flood-depth map

Appendices

A, NOAA Atlas 14 / USGS data

D, GEOHEC-RAS hydraulic report

B, GIS basin parameters

E, Scour & riprap calculations

C, GEOHEC-HMS hydrology report

F, 2D results & figures

01Introduction

Introduction.

1.1 · Project description & location

[Client / Owner] has requested Land & Watersheds to perform a Hydrologic & Hydraulic (H&H) study of [River / Quebrada] at the [crossing / reach], [Barrio, Municipality], Puerto Rico.

The contributing watershed is approximately [00.0] mi². The purpose of this study is to develop design discharges, establish or refine the Base Flood Elevations (BFE) at the crossing, model the river and structure hydraulics in two dimensions, and design scour countermeasures to protect the embankment and structure.

Figure 0 · Project vicinity; replace with site aerial / location map.

1.2 · Scope & purpose

Characterize the contributing watershed and assign hydrologic parameters (area, CN, lag / Tc, channel routing).
Develop design discharges for the 2- to 100- (and 500-) year storms in GEOHEC-HMS.
Model the river reach and the [culvert / bridge] in 2D (GEOHEC-RAS); establish or refine the BFE.
Compute scour and design riprap / countermeasures; support a No-Rise / No-Impact certification if required.

1.3 · Methodology & data sources

Component	Method / Source
Hydrologic method	NRCS UH via GEOHEC-HMS (+ routing)
Rainfall	NOAA Atlas 14, Vol. III (PR & USVI)
Hydraulics	2D unsteady flow, GEOHEC-RAS 2D
Regulatory / scour	FEMA FIS · FHWA HEC-18 / HEC-23
Modeling software	GEOHEC-HMS & GEOHEC-RAS 2D (CivilGEO)

1.4 · Authorization & study area

This study was authorized by [Client / Owner] on [date]. The study area comprises the project parcel and the immediately contributing and receiving drainage, as shown on the effective Flood Insurance Rate Map (FIRM).

Figure 1 · Effective FIRM & BFEDrop FEMA FIRMette / firm panel for the site

Figure 1 · Effective Flood Insurance Rate Map.

Figure 2 · NOAA Atlas 14Drop PF-estimate table / PFDS screenshot

Figure 2 · NOAA Atlas 14 point-frequency estimates.

02Watershed Characterization

Watershed characterization (GIS).

The contributing watershed was delineated from best-available LiDAR / USGS topography and subdivided into [00] sub-basins. Loss (CN), transform (lag / Tc), and channel-routing parameters were assigned from SSURGO soils and land cover, and verified against USGS gage / StreamStats estimates.

Table 2-1 · Watershed parameters
Sub-basin	Area (mi²)	CN	Lag (min)	Tc (min)
B-1	[0.0]	[00]	[00]	[0.0]
B-2	[0.0]	[00]	[00]	[0.0]
B-3	[0.0]	[00]	[00]	[0.0]
…	–	–	–	–

Figure 3 · GIS watershed delineationDrop GIS / HEC-HMS basin & parameter map

Figure 3 · GIS-delineated watershed & parameters.

03Hydrology

Hydrology.

3.1 · Rainfall, NOAA Atlas 14

Design rainfall depths were obtained from NOAA Atlas 14, Volume III, for the site coordinates [lat, long], partial-duration series, for the 24-hour duration.

Table 3-1 · NOAA Atlas 14 rainfall depths (24-hr)
Return period	2-yr	10-yr	25-yr	50-yr	100-yr
Depth (in)	[0.0]	[0.0]	[0.0]	[0.0]	[0.0]

3.2 · Watershed modeling, GEOHEC-HMS

Design hydrographs were developed in GEOHEC-HMS using NOAA Atlas 14 rainfall with NRCS loss / transform and channel routing. Peak discharges at the crossing are summarized below and verified against USGS estimates.

Table 3-2 · Design peak discharge at crossing (cfs)
Storm	Q (cfs)	USGS / regression	Adopted
2-yr	[0.0]	[0.0]	[0.0]
10-yr	[0.0]	[0.0]	[0.0]
25-yr	[0.0]	[0.0]	[0.0]
100-yr	[0.0]	[0.0]	[0.0]

04Hydraulics

Hydraulics.

4.1 · River hydraulics & BFE (GEOHEC-RAS 2D)

A 2D GEOHEC-RAS model of the channel and floodplain was built from the terrain mesh with land-cover roughness and appropriate boundary conditions. Water-surface elevations and the Base Flood Elevations through the reach are reported in Table 4-1.

4.2 · Culvert / bridge & scour protection

The [culvert / bridge] was analyzed under inlet and outlet control; headwater and overtopping are reported for each event. Contraction and local scour were computed per FHWA HEC-18, and riprap / countermeasures sized per HEC-23 and HEC-11.

Table 4-1 · HEC-RAS WSEL / Base Flood Elevation
Station	Q (cfs)	WSEL (ft)
[28.0]	[0.00]	[0.0]
[29.0]	[0.00]	[0.0]
[30.0]	[0.00]	[0.0]

Figure 4 · HEC-RAS 2D mesh / WSELDrop 2D mesh, WSEL profile, or culvert detail

Figure 4 · HEC-RAS 2D mesh & water-surface profile.

05Results & Flood Mapping

Results & flood mapping.

The 2D GEOHEC-RAS model produced maximum flow depths and velocities for the [100-yr] event, mapped below. Results define the floodplain and the Base Flood Elevations and inform the scour and countermeasure design.

Figure 5 · Max flow depthDrop 2D depth raster

Figure 5 · Maximum flow depth.

Figure 6 · Max velocityDrop 2D velocity raster

Figure 6 · Maximum velocity.

06Observations & Conclusions

Observations & conclusions.

Computed Base Flood Elevations through the reach [are consistent with / refine] the effective FIRM by [0.0 ft].
The [culvert / bridge] [passes / overtops at] the [100-yr] event; headwater remains [below / above] road grade.
Recommended scour protection comprises [riprap class / apron length] with a [cutoff wall] keyed to [depth].
[Add project-specific findings, recommendations, and any residual risk or maintenance notes.]

Note: all designs presented herein are schematic and not for construction. Final design is subject to survey verification and permitting.

·Certification

Engineer’s certification.

I hereby certify that this Hydrologic & Hydraulic Study was prepared by me or under my direct supervision, and that I am a duly licensed Professional Engineer under the laws of the Commonwealth of Puerto Rico.

P.E. SEAL
&
SIGNATURE

David Vagnetti, PE

Civil Site & Water Resources Engineer · License No. [#####]

Date: [Month DD, YYYY]

Site Photographs

Photo 1

Photo 2

Photo 3

DRAFT