How Hydrology Modeling Supports Accurate Wetlands Delineation

Computerized hydrology modeling software utilizes sophisticated numeric models to analyze water runoff within a watershed area over a specific time period and rainfall intensity. This advanced technology revolutionizes the assessment of water resources and their impact on project planning. By integrating existing topography, soil types, and vegetation cover, hydrology models can accurately predict water surface elevations and identify areas prone to water inundation within associated water drainages.

The management and regulation of water inundation areas fall under the jurisdiction of the U.S. Army Corps of Engineers, governed by the federal Clean Water Act, as well as the State of California, under the California Environmental Quality Act and Fish & Game Code. These regulatory frameworks ensure that impacts to state and federal waters are carefully assessed and mitigated. Obtaining the necessary permits for projects that impact aquatic resources is essential, and these permits require mitigation measures to compensate for the loss of regulated aquatic resources.

Benefits of Hydrology Modeling

One of the significant advantages of hydrology modeling is its ability to provide valuable insights in situations where field identification of state waters is challenging. Particularly in complex environments such as deserts or areas with intricate water features, accurately identifying state waters through traditional field surveys can be difficult. Hydrology modeling offers a comprehensive and cost-effective alternative. By generating detailed hydrological data, the modeling process allows for the precise delineation and assessment of state waters, which can lead to substantial cost savings and improved efficiency.

Precisely identifying state waters enables projects to mitigate impacts more effectively. This optimization saves both time and money, as it reduces the required compensatory mitigation acreage and streamlines the permit acquisition process. In various scenarios, accurate identification of state waters can result in reduced compensatory mitigation requirements, which directly translates into significant cost savings for project proponents.

Furthermore, hydrology modeling assumes even greater importance due to ongoing discussions and uncertainties surrounding the federal definition of “waters of the U.S.” State regulations often encompass a larger area than federal waters, making it crucial to understand and comply with state jurisdictional requirements. Failure to accurately identify state waters can lead to compliance issues, delays in permit acquisition, and increased costs.

Hydrology Modeling in Action

Dudek has used hydrology modeling to assess project impacts and optimize mitigation strategies on several projects.

Optimized Mitigation in the Desert

In a recent project, Dudek utilized hydrology modeling to assess the compensatory mitigation value of a desert land parcel. To accurately identify state waters, Dudek’s biologists conducted a comprehensive field wetland delineation, mapping existing waters of the State of California.

However, detailed site photography revealed subtle fluvial features that, according to federal and state regulations, might fall within the state’s jurisdiction. To quantify the extent of water inundation during a 10-year storm event within the local watershed, a hydrology model was conducted.

By combining the acreage derived from the field survey with the model’s results, Dudek demonstrated a significantly greater potential for mitigation acreage than initially apparent from the field mapping alone. This enhanced accuracy allowed the project proponent to optimize their mitigation efforts and achieve substantial cost savings.

Hydrology Model Saves Millions on Mitigation

Dudek also recently undertook a project involving the mapping of waters of the State of California to assess potential impacts from a large proposed distribution center. According to the rules set by the California Department of Fish and Wildlife, state waters were identified in steep gullies located within agricultural lands, spanning from top-of-bank to top-of-bank.

However, upon closer examination, Dudek’s experts recognized that some of the gullies exceeded the capacity of their associated watersheds to accommodate stormwater flow. To investigate further, a hydrology model was prepared in collaboration with Stantec. The model revealed a significant finding—the functional top-of-bank was lower than the topographic top-of-bank.

This discovery indicated that the acreage of state waters and the project’s overall impact were overestimated. By providing this fact-based and quantified evidence to the regulatory authority, Dudek successfully reduced the mitigation acreage and saved the client millions of dollars in mitigation costs.

The Bottom Line

Hydrology modeling serves as an invaluable tool for accurately assessing the impacts of projects on state and federal waters. By leveraging advanced numerical models and integrating existing data on topography, soil types, and vegetation cover, hydrology modeling enables precise identification and delineation of state waters.

This optimization of impact analysis and mitigation strategies not only saves time and money but also reduces risks associated with regulatory compliance. With the increasing importance of state jurisdictional areas and ongoing discussions on the federal definition of “waters of the U.S.,” hydrology modeling is a key element in navigating the complex regulatory landscape.

Contact us to learn how we can help you unlock the full potential of your project and ensure compliance with regulatory requirements using hydrology modeling.