Water is powerful. It does what it wants and that can cause a loss of life and damage to property. There has been a significant loss experienced in Oklahoma and Texas, as I have discussed in my previous posts.  But how does water do these things?  There are a few technical and nontechnical terms that describe what water can do.  It’s kind of a force thing.

Hydro force #1

Hydrostatic force is the force of standing water on a solid object; force increases as depth increases.  Imagine slow or still floodwaters.

  • Horizontal:  The weight of the standing water increases (because it weighs more) as the floodwaters get deeper.  It exerts lateral pressure on walls;
  • Vertical (buoyancy): Floodwaters can also cause a building to float off the foundation, or “float” underground utilities, or even unearth coffins.

Result: possible foundation failure and walls collapse or “implode”.  Check out the Village of South Holland’s (Illinois) website.  They have a great description of hydrostatic pressure.

Hydrostatic Pressure

This image is from the Village of South Holland website.  Well done!

Hydro force #2

Hydrodynamic force is the pressure of moving water pushing against a solid object (think your house).  The water causes an impact on the “face” of the structure.  This can cause a separation of the building from its foundation, causing the building to be moved or even wash away.

Not a good scenario 🙁

Impact forces

This is fairly simple.  When stuff smashes into a structure, such as debris (a tree) or waves (usually in the coastal areas), there is an impact.  These types of impacts can cause significantly greater damage than hydrostatic or hydrodynamic forces. Floodborne debris can consist of many exciting items that can cause an impact…vehicles, carports, fences, fuel tanks, parts of other buildings, and more.

Debris left behind from the Ohio River.

Debris left behind from the Ohio River.

Tree lodged against Walkway

There is a large tree jammed against the walkway over the creek. The tree floated down the creek during a flood.

Erosion and scour

Erosion refers to the general loss of soil from a site.  This can happen slowly over time (perhaps due to wave action) or occur very rapidly due to fast-moving water.

When the water is moving quickly, scour can happen.  Scour occurs around an object, such as a piling or part of a foundation.  The fast-moving water eats away at the soil and exposes the foundation of the building.  This can cause a building to shift or collapse.


Due to high velocity, water has scoured this part of the stream channel and exposed these utilities.


This is not something that we have to worry about as much in our area.  Just think of storm surges, tsunamis, and waves hammering buildings.  You get the idea…the wave action can crush things by repeatedly hammering into it.

Ohio River Flooding

This house has been property elevated so flood water and waves do not destroy it.

The flood finale

As it appears from the above examples, water has many methods of getting the win.  Floodwaters can cause damage through different methods; these forces threaten buildings that are in the floodplain.  One role of a municipal entity, such as what we do at the City of Jeffersonville, is to try to keep homes and other structures from being constructed in the floodplain so people do not experience the forces of water.