FLOOD07038

• County: Statewide
• Community: All
• Stream Name: All
• Basin: South Platte
• Title: ASFPM Abstracts, etc. 1994
• Date: 1/1/1994
• Prepared For: ASFPM
• Prepared By: ASFPM
• Floodplain - Doc Type: Educational/Technical/Reference Information

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USE OF HEC-2 FOR FIS REVISIONS:
PROBLEMS AND HOW TO A VOID THEM

by

Joseph B. Chapman!
Moe Khine'
Sue Hoegberg'

HEC-2 is among the most common step backwater program used for preparing and revising
Flood Insurance Studies for the Federal Emergency Management Agency. The computational
procedures utilized by the HEC-2 model can at times result in problems in processing revision
requests. This paper will address several of the more common problems that are encountered and
attempt to provide acceptable methods for avoiding these problems.

Among the problems that will be addressed are: assigning multiple channel 'n' values using NH
cards and the potential problems encountered when developing a floodway; analyzing the impacts
of proposed projects when thl: flow type changes (e.g., Class A Low Flow to Class B Low Flow);
use of 10.41 versus 10.40 for performing encroachment runs. The issues being addressed do not
necessarily reflect errors in the program, but often result in problems during the review of
submittals to FEMA.

Currently, several additional issues are being presented to HEC and it is hoped that these issues,
when resolved, can also be addressed in this paper.

Jospeh B. Chapman, Engineering Section Leader, Dewberry & Davis, 8401 Arlington Boulevard, Fairfax,
Virginia 22031, Tel. [phone]

Moe Khine, P.E., Senior Hydraulic Engineer, Dewberry & Davis, 8401 Arlington Boulevard, Fairfax,
Virginia 22031, Tel. [phone]

Sue Hoegberg, GIS Coordinator, Dewberry & Davis, 8401 Arlington Boulevard, Fairfax, Virginia,
22031, Tel. [phone]