Altering a Watercourse for New Construction

[Emilio Ramirez]

Looking at a 5 acre parcel for subdivision for new residential lot development. About 20% has 100 year flood plain. Anyone have experience modifying an existing FEMA 100 year flood plain and incorporating it into the new drainage plan? It looks like as long as capacity is maintained it should not be an issue. How was the submittal process and timeline to state and federal agencies?

Appreciate any insight. 

[Bryan Wallace]

I work for an engineering firm in Indiana and do that type of work.  If you are altering a waterway in Indiana, you need permits from the U.S. Army Corp of Engineers, Department of Natural Resources, and Department of Environmental Management (not sure of the Colorado equivalents).  The permits vary in length and complexity depending on the amount of linear foot of waterway being impacted, quality of existing waterway etc.  Overall, permits can be simple to obtain, with timelines ranging from a few months to a full year for complex permits.

With regards to FEMA, if you are developing an area and are building it out of the FEMA floodplain, then you will probably need to submit a Letter of Map Revision (LOMR) - your engineer or surveyor will have to do that for you. When you build a property up, you not only must be above the floodplain but must incorporate a Freeboard. This is a safety factor on top of the elevation that FEMA says is the 100 year floodplain. In Indiana, the Freeboard is 2' (based on lowest floor) and a surveyor must create an elevation certificate certifying the FB requirements are met. Contact your local Building Commissioner's office and they should be able to tell you what elevation you need to be at so you are not in the floodplain.

Overall, it will be a permit heavy process due to the waterway, but it can be done.  Just be prepared to wait awhile for permit approvals.  Find a local surveyor / engineering firm that can you help you do this.  You will most likely need their help with the permits and calculations/plans that the permits will require.