What is an Overland Flow Path?

A key idea in flood engineering is the Overland Flow Path (OFP), which is the route that water travels when it surpasses the capacity of the subterranean drainage system and crosses the surface of the land. The OFP is based on the topography of the terrain. If, on the other hand, there is no drainage system, an OFP is produced by the concentration of stormwater runoff when rainfall intensity exceeds soil capacity or strikes an impermeable surface, resulting in runoff. Due to their propensity for flooding and the possibility for property and human harm, these localized pathways are essential for determining the flood hazards associated with any particular location.

Read More: Overland Flow Study Brisbane

From small natural depressions (ponding) to well-established channel beds to man-made constructions in metropolitan settings, Overland Flow Paths can take on a wide variety of shapes and patterns. An overland flow channel in an urban setting might be found in a park, roadway (which is normally made to accommodate certain overland flows), or parking lot—basically, any area where water can flow freely when the drainage systems are overloaded.

The reason you are on this page is probably because you were sent by a building certifier or local council authority to a map that shows the location of a flood overlay. These maps are usually located on the Planning Scheme Policy Flood Overlay Map, or you may have seen them on an interactive mapping or flood report. We usually use topographic analysis, hydrologic modeling, and stormwater infrastructure data in our methods to identify an OFP. Important factors to take into account when evaluating for an OFP are as follows:

Examine the maps provided by the local council.

As our website illustrates, the majority of local councils will have an interactive mapping planning system that will show any potential overland flow patterns. For instance, Brisbane City Council has an interactive map of its planning scheme as well as a map of flood awareness.

Analyzing Topographic Maps

The physical characteristics of the land, such as its height and slope, are described in detail on topographic maps, or contours, which may be used to locate possible OFPs.

Hydrologic Simulation:

Using sophisticated software and some assistance from local and national standards, several design rainfall scenarios (supplied by the BOM) are simulated, and water accumulation and flow locations are observed. At Stormflood, this is what we do. We will determine an OFP’s flood regime, including features like water level, depth, velocity, and Overland Flow Path danger indicators, to help you plan how your development will need to handle the flooding problem.

Verification in the field:

There is no alternative for actually seeing the land, especially during or right after a rainstorm event, even though maps and models are helpful (noting that using data from aerial surveys is very feasible).

Analyzing Past Flood Information:

Particularly in metropolitan settings where man-made constructions may affect water flow, historical flood episodes might provide insight into possible OFPs.

There are several reasons, some of which we’ve included below, to think about hiring a professional flood engineer if you think a property may be impacted by an Overland flow path:

Assessment of Flood Risk:

Determining regions at increased risk of floods can be aided by knowledge of overland flow pathways. Using this knowledge while planning a new building or addition enables the design and execution of suitable flood mitigation methods or flood resilience design.

Designing Infrastructure:

The way water flows around a property can be greatly impacted by the construction and design of a structure or addition. By placing buildings around infrastructure to minimize the effects of flooding, one may lower the danger and damage caused by flooding by having a thorough grasp of the overland flow pathways.

Landscape Architecture:

Designing outdoor elements such as landscaping might benefit from an understanding of overland flow pathways. Water can be directed away from buildings and into suitable drainage areas, for instance, by designing driveways and gardens. In contrast, if the OFP is deemed high velocity, the evaluation can assist in avoiding construction in these high scour zones in order to prevent ongoing upkeep and annoyance to landscaped areas.

Adherence to Regulations:

Overland flow pathways are taken into account at every stage of the planning and building process in most local government units. Failing to do so may incur more expenses, cause delays in planning and building, and even result in fines if an external disturbance is caused at your site.

Objectives of Insurance:

Insurance companies frequently demand knowledge of flood hazards, particularly overland flow pathways, prior to granting coverage. Furthermore, insurance rates may be reduced by proactive risk reduction and proactive understanding of certain risks.

Long-Term Worth of Real Estate:

Proactive measures to lower risk can help buildings or additions that incorporate overland flow patterns preserve or even grow in value over time. In general, properties that have less chance of flooding or that can be proven to have flood concerns through flood documentation are more in demand and can fetch higher prices in the real estate market. It is advised that you contact us to ascertain the extent of the OFP because flood overlay maps are readily obtainable and ignoring them during the property transaction may be interpreted as dishonest behavior on the part of the seller.

One of the most important aspects of flood engineering is recognizing and comprehending Overland Flow Paths. It assists in the efficient management of flood risk by forecasting regions that may flood and providing guidance for the construction of infrastructure that can withstand excessive water. One may map out these routes and make strategic decisions that might help construct flood resilience into your home, lower the risks and premiums associated with flood insurance, and get ready for the destructive consequences of floods by researching the topography, utilizing hydrological models, and looking at past flood data.