Urban Flooding & River Interaction 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-river flood studies.

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

Project understanding.

We are pleased to submit this proposal to conduct the combined urban-stormwater and riverine hydrologic and hydraulic (H&H) study for [Project Name] in [Barrio / Municipality], Puerto Rico, where a developed area is affected by flooding from [River / Quebrada].

The study quantifies on-site stormwater runoff and mitigation while modeling the influence of the adjacent river, its Base Flood Elevations, backwater, and tailwater, on the site, and demonstrates that the development is protected and does not worsen flooding upstream or downstream.

Site conditions

The site sits low in the watershed adjacent to [River / Quebrada], partly within [FEMA Zone AE / A] of the effective FIRM. It drains through an on-site storm-sewer and detention system whose outfall is controlled by the river tailwater. Available data include the civil drainage plans, the effective Flood Insurance Study, NOAA Atlas 14 rainfall, and best-available LiDAR and survey.

Scope of services.

A · Site & data review

• Review of the civil storm-sewer / drainage plans and the effective FEMA Flood Insurance Study (FIS) and FIRM panels.
• Compilation of NOAA Atlas 14, Volume III rainfall depth-duration-frequency data for the site and contributing watershed.
• Compilation of NRCS SSURGO soils and USGS land-cover / gage data for both the urban catchment and the river basin.
• Assembly of best-available LiDAR / topography and survey of the outfall, channel cross-sections, and structure geometry.

B · Urban hydrology & drainage (GeoStorm / SWMM)

• Model pre- and post-development runoff, the storm-sewer network, and detention / LID controls with the GeoStorm EPA-SWMM engine.
• Apply NOAA Atlas 14 design storms (2- to 100-year) and tabulate on-site peak discharges and volumes at the outfall.
• Establish stage-storage / stage-discharge relationships and preliminary outlet sizing for the detention system.

C · Riverine hydrology & 2D hydraulics (GEOHEC-HMS + RAS 2D)

• Develop watershed hydrographs in GEOHEC-HMS and build a 2D GEOHEC-RAS model of the river and floodplain through the developed area.
• Compute Base Flood Elevations, depths, and velocities; map the floodplain and the river's influence on the site.
• Extract the river water-surface at the outfall to define the tailwater / backwater boundary for the drainage system.

D · Interaction & mitigation

• Re-route the detention / outlet design against the river tailwater so post-development peaks do not exceed pre-development peaks under the combined condition.
• Recommend finished-floor / floodproofing elevations and freeboard for at-risk structures relative to the Base Flood Elevation.
• Demonstrate that the development is protected to the design event and produces no adverse upstream or downstream impact.

Methodology & data sources.

Information required from the Owner

All hydrologic, drainage, and regulatory inputs are developed by us. The items required from the Owner to finalize the analysis are:

• Confirmed invert and coordinates of the system outfall to the river (the controlled point of discharge).
• Survey of the channel cross-sections at the outfall and any as-builts of the crossing or outfall structure.

The outfall geometry and the river tailwater together control the routing, and both must be established before the combined analysis can be finalized.

Deliverables.

• Signed and sealed Hydrologic & Hydraulic Report covering methodology, input data, model results, and conclusions.
• Pre- and post-development runoff and detention routing results for the on-site system.
• Base Flood Elevation, depth, and velocity maps from the 2D river model, with the floodplain over the site.
• Tailwater / backwater interaction analysis and the re-checked outlet design.
• Finished-floor / floodproofing recommendations relative to the Base Flood Elevation.
• Supporting figures (FIRM, BFE, storm-sewer plan, 2D mesh) and model files (GeoStorm, GEOHEC-HMS & GEOHEC-RAS 2D).

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 and finished-floor criteria follow local ordinance / owner preference and applicable PRDNER and FEMA standards. A FEMA No-Rise certification, CLOMR / LOMR submittal, or coastal-surge / compound-flood analysis can be added as optional tasks.

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]