Land & Watersheds

Water Resources Engineering · Puerto Rico

Urban Hydrology & Hydraulics

Hydrologic & Hydraulic Study Report

Stormwater, Detention & LID; [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]

GEOSTORM · EPA-SWMM NOAA ATLAS 14 SIGNED & SEALED

Land & Watersheds

Urban H&H Study · 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 · Catchment characterization (GIS)[p]

3 · Hydrology[p]

3.1 Rainfall, NOAA Atlas 14[p]

3.2 Runoff modeling, GeoStorm (SWMM)[p]

4 · Hydraulics[p]

4.1 Storm-sewer conveyance[p]

4.2 Detention / retention & LID routing[p]

5 · Results & flood mapping[p]

6 · Observations & conclusions[p]

Certification[p]

List of Tables

Table 2-1 Catchment parameters
Table 3-1 NOAA Atlas 14 rainfall depths
Table 3-2 Pre/post peak discharges
Table 4-1 Stage-storage-discharge

List of Figures

Fig 1 Effective FIRM
Fig 2 NOAA Atlas 14 PF estimates
Fig 3 GIS catchment delineation
Fig 4 Detention & outlet schematic
Fig 5 Flood-depth map

Appendices

A, NOAA Atlas 14 data

D, Hydraulic / routing report

B, GIS basin parameters

E, Detention & outlet calculations

C, GeoStorm hydrology report

F, Figures & model results

01Introduction

Introduction.

1.1 · Project description & location

[Client / Owner] has requested Land & Watersheds to perform a Hydrologic & Hydraulic (H&H) study for the proposed [Project Name] development at [PR-000, Km 0.0, Barrio, Municipality], Puerto Rico.

The site occupies approximately [00.0] acres and drains toward [receiving system / quebrada]. The purpose of this study is to quantify pre- and post-development stormwater runoff, size the proposed detention and Low-Impact Development (LID) mitigation, and demonstrate that the development does not adversely affect downstream conveyance.

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

1.2 · Scope & purpose

Characterize the contributing catchment and assign hydrologic parameters (area, imperviousness, CN, time of concentration).
Develop pre- and post-development runoff for the 2- to 100-year, 24-hour design storms.
Size and route the detention / retention pond and LID controls; design the outlet structure.
Demonstrate no net increase in peak discharge at the point of compliance, with adequate freeboard.

1.3 · Methodology & data sources

Component	Method / Source
Hydrologic method	NRCS dimensionless unit hydrograph
Rainfall	NOAA Atlas 14, Vol. III (PR & USVI)
Soils / land cover	NRCS SSURGO · USGS MRLC NLCD
Routing	Storage-Indication (Modified Puls)
Modeling software	GeoStorm (CivilGEO), EPA-SWMM engine

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 FIRMDrop 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.

02Catchment Characterization

Catchment characterization (GIS).

The contributing catchment was delineated from best-available LiDAR topography and subdivided into [00] sub-catchments consistent with the proposed storm-sewer layout. Curve numbers were assigned from SSURGO hydrologic soil groups and NLCD/proposed land cover; times of concentration were computed by the [TR-55 / velocity] method.

Table 2-1 · Catchment parameters
Sub-catchment	Area (ac)	% Imp.	CN	Tc (min)
S-1	[0.0]	[00]	[00]	[0.0]
S-2	[0.0]	[00]	[00]	[0.0]
S-3	[0.0]	[00]	[00]	[0.0]
…	–	–	–	–

Figure 3 · GIS catchment delineationDrop GeoStorm / GIS sub-catchment & parameter map

Figure 3 · GIS-delineated catchment & 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 · Runoff modeling, GeoStorm (SWMM)

Pre- and post-development runoff was modeled in GeoStorm (EPA-SWMM engine) using the NRCS dimensionless unit hydrograph. Peak discharges at the point of compliance are summarized below.

Table 3-2 · Pre- vs. post-development peak discharge (cfs)
Storm	Pre (cfs)	Post (cfs)	Post + mitigation
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 · Storm-sewer conveyance

The proposed storm-sewer network (inlets, RCP mains, manholes) was analyzed for capacity under the [10-yr] design storm. All runs convey the design flow with the hydraulic grade line below rim elevations, except as noted.

4.2 · Detention / retention & LID routing

The detention pond (bottom el. [00.00 ft], [2H:1V] slopes) was routed by the Storage-Indication method. The outlet structure combines a [orifice] and [weir] sized so post-development peaks do not exceed pre-development peaks.

Table 4-1 · Stage-storage-discharge
Stage (ft)	Storage (ac-ft)	Discharge (cfs)
[28.0]	[0.00]	[0.0]
[29.0]	[0.00]	[0.0]
[30.0]	[0.00]	[0.0]

Figure 4 · Detention & outlet schematicDrop pond grading / outlet-structure detail or stage-storage curve

Figure 4 · Detention pond & outlet-structure schematic.

05Results & Flood Mapping

Results & flood mapping.

Where surface ponding or 2D behavior governs, a GeoStorm 2D surface model was developed over the project terrain. Maximum flow depths and velocities for the [100-yr] event are mapped below; the mitigated condition keeps water surfaces below [finished-floor / freeboard target].

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.

Post-development peak discharges, once routed through the proposed detention and LID controls, do not exceed pre-development peaks for the analyzed design storms.
The proposed storm-sewer network conveys the design flow with the hydraulic grade line below rim elevations.
The detention pond maintains [0.0 ft] of freeboard above the [100-yr] design water surface.
[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