Discover how one- and two-dimensional hydrologic and hydraulic modeling have become essential tools in modern stormwater management, enabling optimized design solutions, ensuring regulatory compliance, and strengthening long-term resilience for communities.
Stormwater is a natural part of the hydrologic cycle, but in developed environments it often becomes a significant engineering challenge. Instead of infiltrating into the soil, rainfall and snowmelt move rapidly across impervious surfaces – roofs, roads, parking lots, and sidewalks – collecting pollutants and overwhelming drainage systems. The result is familiar to many communities: localized flooding, erosion, infrastructure damage, habitat loss, and degraded water quality.
Effective stormwater management is therefore more than a regulatory requirement; it’s a critical component of public safety, environmental protection, and long-term resilience. To design systems that perform under both everyday conditions and extreme events, engineers rely on robust hydrologic and hydraulic (H&H) modeling tools. Among these, one-dimensional (1D) and two-dimensional (2D) models form the technical foundation for understanding how water moves through watersheds, urban systems, floodplains, and aquifers.
The ability to understand the distinctions between 1D and 2D approaches, and to deploy them effectively, is essential for optimizing design outcomes, identifying flood risk, and achieving compliant stormwater management and enhancing long-term community resilience.
Modern stormwater management must address interconnected objectives: protecting water quality, maintaining infrastructure performance, meeting regulatory standards, enhancing groundwater recharge, and so much more.
H&H modeling provides the analytical framework for meeting these objectives by allowing engineers to:
In this context, the decision to use 1D or 2D modeling is a critical step in the process. Each is built upon distinct assumptions and data requirements, and each is suited to specific types of systems and questions. Understanding these differences is key to selecting the right modeling strategy for you
One-dimensional modeling represents water movement along a single defined path, such as a river, canal, storm sewer, or roadway drainage system. 1D models compute cross-section–averaged values of water surface elevation, velocity, and flow rate at discrete locations along this path.
This approach is particularly effective when:
In these circumstances, 1D modeling offers several advantages. It is computationally efficient, supports long simulation periods and large geographic extents, and is highly developed for representing hydraulic structures such as bridges, culverts, weirs, spillways, gates, levees, and pump stations. For many riverine and stormwater applications, 1D modeling can provide accurate results with a relatively modest dataset and processing footprint.
However, the fundamental assumption of 1D modeling, that flow can be reasonably represented along a line, limits its ability to capture complex spatial patterns. Where water spreads laterally across floodplains, migrates through urban networks in multiple directions, or interacts strongly with local topography, 1D results may no longer be sufficient to characterize risk or support detailed design.
Two-dimensional overland flow modeling extends the analysis from a line to an area. Instead of tracking water along a user-defined path, 2D models simulate flow based on the topography using a mesh of computational elements. With finite-volume methods applied over this mesh, these models compute depth, velocity, and flow direction at each element, allowing water to move in any direction dictated by terrain and boundary conditions.
Because 2D models capture multiple flow paths and small-scale variations in topography, they can provide a much more detailed and realistic representation of stormwater behavior than 1D models in these settings. Outputs such as depth grids, velocity maps, and time-varying inundation extents support more informed planning, design, and communication with stakeholders and regulators.
The tradeoff is computational and data intensity. High-resolution topographic data, flexible meshes, and long simulation periods can be demanding, particularly over large domains. As a result, 2D modeling is most powerful when thoughtfully scoped and paired with a modeling engine designed to manage complexity efficiently.
Stormwater systems do not operate solely at the surface. Subsurface conditions, such as aquifer characteristics, groundwater mounding, seepage, and interactions between surface water bodies and surficial aquifers, can strongly influence both short-term flooding and long-term system performance.
Two-dimensional groundwater modeling, employing finite element methods, provides a way to quantify:
When integrated with 1D and 2D surface flow models, 2D groundwater simulations allow engineers to more fully assess retention pond recovery, wetland behavior, long-term storage, and water budgets. This integrated perspective is especially important in systems where infiltration-based practices, wetlands, and shallow aquifers are key elements of stormwater strategy.
In practice, the question is rarely “1D or 2D?” in isolation. Instead, engineers must consider project objectives, data availability, computational constraints, and regulatory expectations.
1D modeling is often appropriate for:
2D modeling is preferred when:
In many cases, the optimal solution is a coupled 1D/2D approach. Channels and storm sewers are represented in 1D to leverage efficiency and advanced structure modeling, while adjoining floodplains, urban areas, or interior basins are modeled in 2D.
Properly integrated, these hybrid models allow water to move between domains, capturing the strengths of both approaches within a single framework.
For more than 40 years, StormWise™ has provided a widely accepted H&H modeling engine for engineers and water resources professionals. Its long history of regulatory acceptance, including national recognition by FEMA for NFIP-related applications, has made it a trusted platform for watershed modeling, land development, roadway drainage, floodplain mapping, water budget analysis, and so much more.
StormWise offers a flexible, scalable system that supports:
These capabilities are complemented by georeferenced graphical tools, automated data takeoff from maps, customizable 2D meshes, animation of water surface profiles and flood extents, and comprehensive reporting and visualization options.
Together, they position StormWise as a vital tool for:
As communities continue to urbanize and storm events grow in both frequency and intensity, stormwater management must be informed by accurate, defensible, and adaptable modeling tools.
Understanding the roles of 1D and 2D modeling, and the added value of integrated surface and groundwater analysis, enables engineers to select the right level of complexity for each project, deliver more reliable designs, and make better use of resources.
StormWise provides a proven, technically robust platform that unifies these capabilities within a single modeling environment. By combining trusted 1D H&H modeling with fully integrated 2D overland and groundwater simulation, StormWise helps engineering professionals move beyond simple compliance toward proactive, resilient, and sustainable stormwater management
To explore how StormWise’s fully integrated 1D and 2D modeling capabilities can enhance your team’s stormwater planning and management, contact our team today!