The field of civil engineering is extensive and encompasses many fields of expertise. A successful land development project requires input and expertise from professionals in many fields. One of these fields of expertise is hydrology and hydraulics. The following article will describe the field of hydrology, why hydrologic engineering is essential, and where you can find a competent hydrologist or hydrologic engineering professional for your project.
What is hydrology?
Hydrology is a field of study that is concerned with the flow of water over the land surface. Hydrology is often discussed along with hydraulics which describes the study of flow through streams, channels, and pipes. Hydrologists use a wide range of tools, including modeling software, mathematical equations, topographic information, weather data, and statistical analysis to understand how water flows over a site (e.g., volume, velocity, water surface, etc.). Understanding drainage patterns helps designers and engineers ensure that a project will be constructed in a way that minimizes flood risk.
Why is hydrology important?
Understanding the hydrology of a site allows property owners to effectively manage stormwater runoff to ensure water drains away from buildings and does not flood neighboring properties. Some examples of reports associated with such requirements are discussed in the following sections.
Hydrology Studies
Hydrology studies are required for land development projects that alter drainage patterns, subdivisions, conditional use permits (CUP), or other conditions that are specific to a particular municipality. For example, Los Angeles County requires a Hydrology Study for all projects with a proposed public drainage system that will ultimately be transferred to the Los Angeles County Flood Control District (LACFCD). A Hydrology Study describes the existing condition (e.g., flows, time of concentration, drainage features, the existence of FEMA floodplains, etc.) and the proposed condition. In addition, a Hydrology Study will include a description of the proposed condition, a summary of the drainage design concept, and a description of how the impacts of the proposed development project will be mitigated.
Water Quality Management Plans (WQMP)
A Water Quality Management Plan (WQMP) describes how stormwater runoff will be addressed after construction is completed. Project-specific WQMPs are part of the National Pollutant Discharge Elimination System (NPDES) program and detail how the water quality impacts of the development project will be mitigated. Development projects are categorized as priority projects and non-priority projects. The difference between these two categories is the low-impact development (LID) requirements. Because the Project WQMP could affect the site layout, it is best to prepare a WQMP early in the design process.
WQMPs also discuss potential hydromodification. Hydromodification is a term that refers to changes in stream flows and associated sediment loads (aggradation and degradation) due to changes in the watershed’s land use or hydrology. Specifically, a Project WQMP evaluates potential Hydrologic Conditions of Concern (HCOC).
Stormwater Pollution Prevention Plans (SWPPP)
A Stormwater Pollution Prevention Plan (SWPPP) is a project-specific document that identifies potential sources of pollution on a construction site and how to mitigate the impact of these pollutants. All projects larger than one acre in size are required to have a SWPPP.
Need a hydrologic engineer?
If you need help understanding the hydrology of your site, please reach out to Surf City Hydraulic Engineering at info@surfcityh2o.com for a free quote and consultation.