In recognition to a growing need for increased clarity and consistency of expectations for the acceptable methods of performing a breach analysis and determining the hazard both for small ponds and large dams, the Dam Safety Division has developed the following guidance document and supporting worksheets.
If a dam has been determined to be a Significant or High Hazard, an Emergency Action Plan (EAP) must be prepared in accordance with Maryland law. Templates and supporting resources for EAP development is provided at the following link:
The following spreadsheets may be used to compute flows through a riser and an open channel emergency spillway. Flows through a standard riser or a slotted multiple opening riser can be computed.
A runoff depth table based on the Soil Conservation Service TR-55 Runoff Equation is provided. The runoff table can also be used to determine the rainfall amount necessary to generate the 50% probable maximum flood. Precipitation depths for various storm durations and frequencies should be determined using the NOAA Atlas 14 Precipitation Data Frequency Server website.
Phreatic Surface Estimation Spreadsheets
This spreadsheet uses the Casagrande Graphical Method to determine the phreatic seepage surface through a dam and estimates the seepage amount.
The following executable programs are used to determine breach flows and routed breach flows downstream of dams. The "hec1vm" program is a user friendly editor program for the HEC-1 Model as well as run the HEC-1 Program. The HEC-1 Program will develop flood hydrographs and breach hydrographs and route the downstream flows through stream cross sections, roads and other dams. The "smpdbk" (Simple Dam-Break) program is a shortcut version of the National Weather Service full Dam-Break Model. This program will determine breach flows from dams and route flows through downstream cross sections but is limited because it will not route flows through and over downstream roads and dams.
Model Input Files
The "hec1 data" file contains several dam breach examples with downstream flood routings. The data can be used as a input guide for computing a danger reach for your dam. The "smpdbk" file contains several input and output examples using the National Weather Service Simple Dambreak Program.
US Army Corps of Engineers' HMR52 Program
This program is used to determine the elliptical rainfall distribution for dams with drainage areas larger than 10 square miles. The program outputs a rainfall hyetograph (rain depth vs. time) for the watershed areas above and below the dams. The output data is used as input in the HEC-1 Model to generate storm hydrographs. The model predicts smaller elliptical rainfall bands moving further away from the storm center.
You may also call us at (410) 537-3538. Our mailing address is:
Dam Safety DivisionWater Management AdministrationMaryland Department of the Environment
1800 Washington Boulevard, Ste. 440Baltimore, Maryland 21230-1708
1800 Washington Boulevard, Baltimore, MD 21230