Drainage Analysis

At Legacy Engineering, our Drainage Analysis services are designed to protect your project from flooding, regulatory delays, and costly redesigns. Whether you are developing a single property or planning a full subdivision, we evaluate how stormwater moves across your site and how proposed improvements will change natural flow patterns.

We begin by reviewing existing drainage conditions including topography, soils, upstream watersheds, downstream constraints, and known flood hazards. From there, we model runoff, identify capacity limitations, and design solutions that safely convey stormwater away from structures, roadways, and neighboring properties.

For smaller sites and isolated improvements, we utilize time-tested methods such as the Rational Method and unit hydrograph approaches to calculate runoff, size culverts, and design detention systems efficiently and conservatively.

For larger tracts, subdivisions, and master-planned developments, we apply advanced 2D hydrologic and hydraulic modeling to simulate real-world storm behavior across the entire site. This allows us to account for overland flow, road overtopping, backwater conditions, and floodplain interactions with a level of accuracy that cannot be achieved through simplified calculations alone.

• Our drainage engineering services include:

• Watershed and sub-watershed delineation

• Hydrologic analysis for minor and major storm events

• Rational Method analysis for small drainage areas

• 2D overland flow modeling for complex or large-scale developments

• Detention and retention pond sizing and outlet structure design

• Culvert, storm drain, and open-channel system design

• Floodplain verification and mitigation planning

• Erosion and sediment control design

• Drainage reports and permit documentation

• Coordination with reviewing agencies and floodplain administrators

Our goal is not just to produce calculations — it’s to create constructible, cost-effective drainage designs that stand up to review and perform in the field. We design systems that protect infrastructure, reduce long-term maintenance costs, and provide confidence that your investment is prepared for real storm conditions, not just minimum code requirements.

Whether you are planning a new development or correcting existing drainage issues, Legacy Engineering provides clear, defensible engineering solutions for projects of any scale.