Adoption of the AASHTO Drainage Manual by
the Montana Department of Transportation
The Hydraulics Section (Preconstruction Bureau, Engineering Division) of MDT has
been revising chapters of the AASHTO Model Drainage Manual, to reflect the current
procedures of the MDT Hydraulics Section.
• Chapter 7, Hydrology, was adopted October 3, 1995.
• Chapter 9, Culverts, was adopted May 16, 1996.
• Chapter 10, Bridges, was adopted July 22, 1997.
• Chapter 13, Storm Drainage Systems was adopted May 21, 1998.
The numbering system currently used is that from the Model Drainage Manual. The
chapters that have been adopted supersede the information provided in the Montana
Department of Highways Hydraulics Manual, dated September 1, 1975.
The end of this document contains a Table of Contents for the Model Drainage Manual.
Not all of these chapters relate to work done by MDT's Hydraulics Section, nor are they
necessarily applicable to MDT projects. The Table of Contents is provided here for
information only. Questions concerning this document should be directed to Mark
Goodman, MDT Hydraulics Section, 406/444-6247. This manual is written for use by
professional engineers trained in hydraulics, and is not intended to completely cover the
subject of highway hydraulics.
This document has been created in WordPerfect 6.1, and includes text and graphics.
Importing this document into other wordprocessing software, or other versions of
WordPerfect, may create some format and/or graphics problems. Those portions of the
Model Drainage Manual that are unique to MDT are shown in bold.
The following list contains changes that have been made to the chapters since their
original issue. All changes will include an effective date, along with a description of the
change. For deletions and additions, the description will include simply what was deleted
or added. For changes, the description will include the previous criteria and the new
criteia. These changes are approved using the same procedure that the original chapters
use, which includes a review by a committee of Hydraulics staff members, followed by
review by the Preconstruction Engineer and FHWA. It is the users responsibility to check
this document regularly for changes.
Changes to Hydrology Chapter 7
9/17/97 Deleted nomograph for Mannings Equation (figure 7-3). Renumbered other
figures.
9/17/97 In Appendix B, corrected the list of weather stations, changing Gibbons Pass
from Deer Lodge County to Beaverhead County.
2/17/98 On page 7-38, corrected Cf for the 50 year flow from 1.25 to 1.2. The Q50
was corrected from 68 cfs to 66 cfs.
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Changes to Hydrology Chapter 7
2/17/98 In Appendix A, Page 7-A-5, deleted the reference to Chapter 5 as a location
for Procedure Memorandum No. 5. This Procedure Memorandum will likely
be placed in a different chapter.
2/17/98 In Appendix A, Page 7-A-12, changed the discount rate to 7.125%, as
reported in the November 7, 1997 Federal Register.
2/17/98 In Appendix B, added daily precipitation data for 219 stations.
5/28/04 On page 7–36, revised Channel Geometry USGS Report Number to 03–4308
to reflect new USGS publication.
5/28/04 At some time after 2/17/98, the Daily Precipitation tables were inadvertently
removed from Appendix B. This revision adds the Daily Precipitation table
back into Appendix B.
6/17/04 On page 7–67, corrected exponents in equation 7.24. Equation 7.24 is
tc = (l0.8 (S + 1)0.7) / (1140 Y0.5)
9/8/04 On page 7–59, percentages reflecting conditions for Open Space were moved
from 'Average Percent Impervious Area' to corresponding condition under
'Cover Type and Hydrologic Condition.'
Changes to Culvert Chapter 9
9/18/97 Added relationship between peak flow and runoff, for use in Wyoming Hydrograph
Method, to Appendix G. This relationship was developed from analysis of 18 events
documented by USGS at five gaging sites.
9/18/97 Added USGS Water Supply Paper 2056 to Reference list.
6/10/99 Revised section 9.3.4; pages 9-12; references to optional pipe policy.
2/16/00 Appendix E pages 9-E-2, 9-E-3, 9-E-4, and 9-E-5 were revised to reflect that fiber
bonded CSP is no longer commercially available and should not be specified. Also
note on page 9-E-4 that ploymeric coating is available to 0.138" thickness.
Changes to Storm Drain Chapter 13
6/22/04 On page 13–18, Table 13–1, the last 4 access hole sizes were increased to 54". A 36"
pipe is too large for a 48" access hole.
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AASHTO Model Drainage Manual, 1991
Table of Contents
Chapter Number Title
1 Introduction
2 Legal Aspects
3 Policy
4 Documentation
5 Planning and Location
6 Data Collection
7 Hydrology
8 Channels
9 Culverts
10 Bridges
11 Energy Dissipators
12 Storage Facilities
13 Storm Drainage Systems
14 Pump Stations
15 Surface Water Environment
16 Erosion and Sediment Control
17 Bank Protection
18 Coastal Zone
19 Construction
20 Maintenance of Drainage Facilities
21 Restoration
Note: Bold lettering indicates formal adoption of the chapter, and inclusion of MDT guidelines,
by MDT Hydraulics Section. Other chapters are listed for reference only.
Page 3 of 3
