Stormwater, Detention & Low-Impact Development Study

Focused expertise, one engineer, every project.

Land & Watersheds is, admittedly, a one-person operation, but what I lack in staff meetings, I more than make up for in focused expertise and personal attention to every project.

As a water resources engineer, I specialize in hydrologic and hydraulic analysis, drainage design, stormwater management, watershed assessment, and site-improvement design. I work with residential property owners, developers, and municipalities across Puerto Rico to solve complex drainage problems, design site improvements that work with natural hydrology, assess environmental impacts, and ensure regulatory compliance.

My approach combines rigorous technical analysis with practical, site-specific solutions that actually work in the field, not just on paper. Whether you are dealing with unexpected flooding, erosion issues, grading and drainage plans for your development, or permitting challenges, Land & Watersheds provides the specialized knowledge and dedicated service that only comes from working directly with the engineer handling your case. No hand-offs, no miscommunication, just straightforward expertise when you need it most.

David Vagnetti

Civil Site & Water Resources Engineer

David believes in free enterprise and individual responsibility, which is why he left the corporate world to build Land & Watersheds. He prides himself on personal service and an artistic eye, and enjoys helping clients in flood-prone areas realize that, in many cases, “it does not have to be that way.”

Selected urban drainage & stormwater projects.

This list is by no means exhaustive; many more available upon request.

Project understanding.

We are pleased to submit this proposal to conduct the hydrologic and hydraulic (H&H) study supporting the proposed [Project Name] development along [PR-000 at Km 0.0], [Barrio / Municipality], Puerto Rico.

The study quantifies stormwater runoff under pre- and post-development conditions, sizes the proposed mitigation (detention/retention pond and Low-Impact Development controls), and demonstrates that the development does not adversely affect downstream stormwater conveyance.

Site conditions

The site drains toward an existing public stormwater conveyance system. A detention pond has been preliminarily configured with a bottom elevation of [00.00 ft] and [2H:1V] fill slopes. The proposed on-site collection system consists of inlets, reinforced-concrete-pipe (RCP) storm-sewer mains, manholes, and an outlet structure discharging to a downstream connecting manhole. The project area has been subdivided into [00] contributing sub-drainage areas, which will be carried forward in the analysis.

Scope of services.

A · Site & data review

• Review of the preliminary Storm Sewer Plan and supporting site information provided by the Owner.
• Compilation of NOAA Atlas 14, Volume III rainfall depth-duration-frequency data for the project location.
• Compilation of NRCS SSURGO soils data to assign hydrologic soil groups (HSG).
• Compilation of USGS MRLC National Land Cover Database (NLCD) data to characterize pre-development land cover.

B · Pre-development hydrologic analysis

• Delineate contributing drainage areas from available topography; assign curve numbers (CN) from SSURGO HSG and MRLC land cover.
• Estimate times of concentration and generate runoff hydrographs using the NRCS dimensionless unit-hydrograph method with NOAA Atlas 14 design storms (typically the 2-, 5-, 10-, 25-, 50-, and 100-year, 24-hour events).
• Tabulate peak discharges and runoff volumes at the project’s point of discharge.

C · Post-development hydrologic analysis

• Repeat the analysis for the proposed condition, updating curve numbers for roofs, pavements, lots, green areas, and proposed units.
• Maintain the sub-drainage areas identified on the civil plans for consistency; compute peak discharges and volumes at the same point of discharge for the same design storms.

D · Mitigation, detention / retention & LID routing

• Develop stage-storage and stage-discharge relationships for the proposed pond and LID controls from the design geometry.
• Size the outlet structure (orifice/weir combination) and verify performance through reservoir routing (Storage-Indication / Modified Puls).
• Demonstrate that post-development peak discharges leaving the pond do not exceed corresponding pre-development peaks for each design storm, with adequate freeboard.

Methodology & data sources.

Information required from the Owner

All hydrologic inputs (rainfall, soils, land cover, drainage areas, and pond geometry) are developed by us. The only items required from the Owner to finalize the analysis are the survey items at the downstream connection:

• Confirmed invert elevation of the downstream connecting manhole (the point of discharge).
• Confirmed horizontal location (coordinates) of that same manhole.

These two values control the outlet hydraulics and the tailwater condition for the routing, and must be well established before the routing can be finalized.

Deliverables.

• Signed and sealed Hydrologic & Hydraulic Report covering methodology, input data, model results, and conclusions.
• Tabulated pre- and post-development peak discharges and runoff volumes for each design storm.
• Stage-storage, stage-discharge, and stage-elevation relationships for the proposed pond and LID controls.
• Outlet-structure sizing and design water-surface elevations (with freeboard).
• Supporting figures: pre- and post-development drainage-area maps, soils map, and land-cover map.
• Electronic model files (GeoStorm / EPA-SWMM).

Assumptions, exclusions & client-provided information.

This scope assumes access to existing survey/as-builts, right-of-entry for limited site reconnaissance if desired, and availability of best-available topography. Excluded (can be added by amendment): new topographic survey, subsurface investigations, geotechnical design, environmental permitting, and final construction documents.

Calibration beyond reasonableness checks is excluded; if requested, we can develop a calibration plan using nearby USGS gages or high-water-mark data. Freeboard criteria and roadway serviceability standards follow local ordinance/owner preference; if a regulatory freeboard is specified by PRPB/municipality, we apply it and document compliance. Coastal surge or compound flooding, if relevant, can be included as an optional task with joint-probability analysis.

Fee summary.

Proposal excludes survey costs and assumes schematic (not-for-construction) designs. Valid for 30 days after submission.

Schedule & timeline.

Terms & conditions.

• Unless amended in writing, the contents of this proposal supersede any plans or verbal discussions.
• Materials, equipment, and methods specified will at all times meet or exceed building codes.
• Land & Watersheds is not responsible for deficiencies, errors, or omissions that are a direct result of the survey data or geotechnical report.
• Land & Watersheds will provide the services outlined in this proposal.

Acceptance & sign-off.

Land & Watersheds proposes the services outlined herein for an all-inclusive fee of [$7,280.00]. Additional charges will be incurred if the project scope changes after this document is signed. The next step is to agree to this proposal (with any noted changes) and sign the contractual agreement that references it.

Land & Watersheds · Water Resources Engineering · Puerto Rico · [email] · [phone]