Jan 25 2012

What Every Floodplain Manager Needs

In the Netherlands there are 25 Water boards, similar to U.S. levee boards or reclamation districts.  Each board has a president or chair known as the Dijkgraaf

During his or her first day on the job, a Dijkgraaf is given many responsibilities – and one present.  A pair of Wellington Boots.  In the Netherlands where the historical mantra has been “droge voeten”  (dry feet), this small gift is quite appropriate to remind the Dijkgraaf that if his or her region floods, he or she will be responsible and accountable, and he or she will be out on the front lines fighting the flood.  (from; Great gift ideas for your local flood manager, The Water Away)


We could all use a gift that reminds us of the importance of our jobs and the responsibilities they come with, and with the boots the reminder can be more than symbolic.  For flood plain managers there is something else that is needed to perform there jobs well that often gets over looked or under rated; good digital elevation/terrain data.

The floodplain you manage is going to be determined by the exact extents of a flood at some specific return interval like the 100-yr flood. The better the elevation data the more accurate the flood extents can be mapped at various flood levels.  Knowing where or who is going to get wet at what flow is really important for the manger to know so that he/she can communicate that information to the people who may be impacted.

The flood levels are determined by hydraulic models which are heavily influenced by, you guessed it, good elevation data. While good elevation data does not automatically mean a hydraulic model is correct, it is the first and most important piece needed to produce an accurate model. Check out what the National Research Council (NRC) says in Mapping the Zone;

Topographic data are the most important factor in determining water surface elevations, base flood elevations, and the extent of flooding and, thus, the accuracy of flood maps in riverine areas.

The largest effect by far on the accuracy of the base flood elevation is the accuracy of the topographic data.

At the International LiDAR Mapping Forum (ILMF) in Denver, CO this week there was a discussion about quantifying the value of a national enhanced elevation dataset.  The current National Elevation Dataset (NED) of the USGS is 30-50 years old, and does not meet the requirements needed for accurate flood mapping. The possible uses for up to date, more accurate data sets are endless, but the top 10 business uses (in order of priority, with the top being the most important) are:

  • Flood risk management
  • Infrastructure and construction management
  • Natural resources conservation
  • Agriculture and precision farming
  • Water supply and quality
  • Wildfire management, planning and response
  • Geologic resource assessment, hazard and mitigation
  • Forest resource management
  • River and stream resource management
  • Land navigation and safety

I found it interesting that of the top 10 business uses 2 are specific to rivers and riverine corridors, and arguably 4 others have some overlap with rivers and water.

So if you’re a flood plain manager do you have what you need?

  1. How old is the data you use for your modeling and map production?
  2. How was it collected?
  3. How accurate is it?
  4. Is it from one seamless dataset or a patchwork of varying datasets?
  5. Does it include hydrographic survey data in the channel if needed?

Before you model, map, plan, and manage, make sure you are starting from a solid foundation.

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