MnDOT Design-Build Program
Federal Project No. [insert #]
12
DRAINAGE
12.1
General
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
This Section identifies the design and construction requirements associated with temporary and permanent
drainage, including culverts, storm sewer systems, bridge hydraulics, roadway ditches, permanent and
temporary erosion and sediment control, structural pollution control devices, storm water ponds, and
infiltration/filtration features.
12.2
Administrative Requirements
12.2.1
Standards
In the event of a conflict between the standards set forth in Book 3 relating to drainage, follow the order of
precedence as set forth below:
 MnDOT Special Provisions
 MnDOT Technical Memoranda
 MnDOT Standard Specifications for Construction
 MnDOT Drainage Manual
 MnDOT Road Design Manual
 MnDOT Standard Plates Manual
 MnDOT LRFD Bridge Design Manual
 AASHTO LRFD Bridge Design Specifications
 MnDOT Pavement Manual
 MnDOT Geotechnical and Pavement Manual
 MnDOT State Aid Manual
 MNDNR Best Practices for Meeting DNR General Public Waters Work Permit
 MPCA Minnesota Stormwater Manual
 FHWA Hydraulic Design Series No. 7, Hydraulic Design of Safe Bridges
 FHWA Hydraulic Design Series No. 2, Second Edition, Highway Hydrology
 FHWA Hydraulic Design Series No. 3, Design Charts for Open Channel Flow
 FHWA Hydraulic Engineering Circular Number 14 (HEC-14), Hydraulic Design of Energy
Dissipators for Culverts and Channels
 FHWA Hydraulic Engineering Circular Number 15 (HEC-15), Design of Roadside Channels with
Flexible Linings
 FHWA Hydraulic Engineering Circular Number 17 (HEC-17), The Design of Encroachments on
Flood Plains using Risk Analysis
 FHWA Hydraulic Engineering Circular Number 18 (HEC-18), Evaluating Scour at Bridges
 FHWA Hydraulic Engineering Circular Number 21 (HEC-21), Design of Bridge Deck Drainage
Systems
 FHWA Hydraulic Engineering Circular Number 22 (HEC-22), Urban Drainage Design Manual
 FHWA Hydraulic Engineering Circular Number 23 (HEC-23), Bridge Scour and Stream Instability
Countermeasures: Experience, Selection and Design Guidance, Volumes 1 and 2
RFP
Drainage
12-1
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
 U.S. Geological Survey (USGS), Generalized Skew Coefficients for Flood-Frequency Analysis in
Minnesota
 Remaining standards set forth in Book 3
12.2.2
Meeting Requirements
12.2.3
Equipment/Software
See Exhibit 12-A for the list of approved drainage design software that may be used on the project. Use
spreadsheet output formats that are consistent with output described in the MnDOT Drainage Manual.
Provide the following specific equipment/software:
12.2.4
Permits/Authorizations
12.2.4.1 Coordination with Other Agencies and Disciplines
Coordinate all water resource issues with affected interests and regulatory agencies. Document the resolution
of issues, including memoranda for the record. Coordinate this work with Section 4.
12.3
Design Requirements
12.3.1
General
Design facilities compatible with existing drainage systems adjacent to the Project and preserve existing
drainage patterns wherever possible unless directed otherwise in this Section 12 or Approved by MnDOT.
Where drainage patterns must be changed from the existing, secure all permits and drainage easements.
Design drainage to accommodate construction staging and provide drainage during all stages of construction.
Provide temporary and permanent drainage design details for each stage of construction in the SWPPP.
Include temporary erosion control ponds and other BMPs needed to satisfy the NPDES and other regulatory
requirements.
12.3.2
Investigations/Supplemental Work
12.3.2.1 Data Collection
Identify all water resources issues, utilizing available data, including water quality requirements as imposed
by appropriate local, state, and federal government regulations; National Wetland Inventory and other
wetland/ public waters inventories; and official documents concerning the Project, such as the environmental
studies. Acquire information on municipal drainage systems draining to the project and watershed standards
and rules.
Water resource issues include, but are not limited to, areas with historically inadequate drainage (flooding or
citizen complaints), environmentally sensitive areas, localized flooding, and maintenance problems
associated with drainage and areas known to contain contaminated soil or water. Identify watershed
boundaries, DNR-public waters, county ditches, areas classified as wetlands, impaired waters (based on total
maximum daily load [TMDL]), special waters, contaminated soil areas, groundwater table elevations where
infiltration or filtration is proposed, floodplains and Drinking Water Supply Management Areas
(DWSMA’s). This includes the degree of vulnerability of each DWSMA and karst areas throughout the
project area.
Acquire existing storm drain plans and survey data, including all data on culverts, drainage systems, and
storm sewer systems within the Project area. Determine existing drainage areas that contribute to the
highway drainage system and the estimated runoff used for design of the existing system.
RFP
Drainage
12-2
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
MnDOT Design-Build Program
Federal Project No. [insert #]
Obtain additional photogrammetric and geographic information system (GIS) data for the Project area that
depicts the outstanding resource value waters and impaired waters. Conduct surveys for information not
available from MnDOT or other sources.
ESRI GIS shapefiles of storm drainage features in the Project area that have been recorded in the
HYDINFRA database will be provided by MnDOT.
12.3.3
Design Criteria
12.3.3.1 Project-Specific Requirements
12.3.3.2 Stormwater Storage and Treatment Facilities
In addition to the requirements in Exhibit 12-B (Stormwater Storage Facilities), comply with the following
requirements for stormwater storage facilities:

Design and construct stormwater storage facilities with a minimum berm crest width of 5 feet.

Design and construct all stormwater facilities outlet structures using grates or trashracks located on
outlet structures.
12.3.3.2.1
Wet Stormwater Ponds
Line stormwater ponds and filtration basins if they are located within a very high or a high vulnerability area
of a drinking water supply management area (DWSMA) or located within contaminated soils.
12.3.3.2.2
Infiltration Basins
Provide for pretreatment of runoff before it enters the infiltration basin by removing 70% of Total Suspended
Solids from the stormwater. Analyze removal efficiencies based on historical rainfall data. Provide pretreatment facilities for each basin to remove settleable solids, floating material, oil and grease from incoming
runoff. Infiltration basin cannot be used during construction as a temporary sediment basin.
Blend the upper 12 inches of the infiltration basin with compost, in-situ soils or sand to establish plant
growth. Construct the upper 12 inches with a maximum of 20-percent Grade 2 Compost by volume.
Construct the remaining volume of material in the upper 12 inches of either in-situ soils or sand to meet the
required infiltration rate. Obtain approval from MnDOT for the native plant growth prior to final acceptance
of basins.
12.3.3.2.3
Filtration Basins
Provide for pretreatment of runoff before it enters the basin by removing 70% of Total Suspended Solids
from the stormwater. Analyze removal efficiencies based on historical rainfall data. Provide pre-treatment
facilities for each basin to remove settleable solids, floating material, and oil and grease from incoming
runoff. Filtration basins are not to be used as a temporary sediment basin during construction if the filter
media is in the basin.
Extend filtration basin media to a minimum depth of 3 feet below the filtration basin surface. Use Fine Filter
Aggregate and a maximum of 20 percent Grade 2 Compost for the upper 12 inches of the filtration basin
media. Obtain approval from MnDOT for the native plant growth prior to final acceptance of basins.
12.3.3.2.4
Structural Pollution Control Devices (SPCD’s)
SPCD’s are not to be used on this project.
Analyze SPCD’s based on the particle size distribution table provided below to determine the Total
Suspended Solid (TSS) removal efficiency of the device. Analyze the SPCDs based on historical rainfall data
extending for a minimum of 10 years. Design the SPCDs based on MnDOT completing maintenance on the
structure once per year
Particle Diameter,
microns
RFP
Drainage
Percent of Sediment
Finer
12-3
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
MnDOT Design-Build Program
Federal Project No. [insert #]
12.3.3.2.5
1100
92.5
820
72
250
42
100
21
41
8
Access to Stormwater Facilities
Provide a maintenance access with maximum slope of 8 percent for each stormwater storage facility
comprised of suitable grading material with topsoil and vegetation. Grade slopes no steeper than 1:3 between
the maintenance access and the stormwater pond NWL or infiltration/filtration basin bottom.
12.3.3.2.6
Infiltration and Filtration Area Signage
Mark infiltration and filtration areas with Approved MnDOT signs (X3-6A) indicating area is “infiltration
area” or “filtration area.” Place signs in locations as directed by MnDOT. If liners are used on filtration
features, place signs on top of the berms, so as not to damage the liner of filtration features.
12.3.3.3 Hydrologic Methods
Design all hydraulic infrastructure based on MnDOT Technical Memorandum No. 13-08-B-04 (Atlas 14).
Design the overall drainage system such that the runoff rates for the proposed project do not exceed the
existing runoff rates for the 2-, 10-, and 100-year storm events for all points where stormwater leaves the
project site.
Design the drainage system so pre-Project conditions are not exceeded for flood damage potential.
Design stormwater storage and treatment facilities using the 100-year, 24-hour rainfall event with an
antecedent moisture condition of 2.
Design storm sewer systems, including local roadways, based on a minimum 10-year design frequency,
unless otherwise noted. Design pavement drainage for local roadways using the spread criteria in the State
Aid Manual.
Design interstate highway sag points such that the spread for the 50-year storm is confined to the shoulder
area and at least one lane in each direction is free from water for the 100-year storm.
Permanent dewatering is not allowed.
12.3.3.4 Hydraulic Structures
Complete a Risk Assessment and Hydraulics Recommendation Letter for all structures greater than 48 inches
in diameter. Submit these documents and all supporting hydraulic models and computations to MnDOT for
Acceptance.
See Exhibit 12-C (Hydraulic Structures) for additional design requirements.
Include flood-routing computations with the culvert or bridge analysis when the culvert or bridge design is
influenced by upstream storage.
12.3.3.4.1
Culverts
Analyze the proposed culverts in accordance with Exhibit 12–C.
RFP
Drainage
12-4
MnDOT Design-Build Program
Federal Project No. [insert #]
12.3.3.4.2
Bridges
12.3.3.4.3
Storm Drains and Sewer
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
Design pipes with a minimum flow velocity of 3 fps and a maximum of 15 fps. If geometric constraints
prohibit the minimum velocity, design pipes with flow velocities less than 3 fps for full flow at 80 percent of
the internal diameter to account for sedimentation in the pipe. Design other storm drain pipes using the full
internal diameter. Do not design storm drains for greater than full-flow capacity at the design flow rate.
Provide pipe outlets with temporary or permanent energy dissipation within 24 hours after connecting the
pipe to any constructed or existing surface waters.
Locate storm sewer manholes outside of the driving lanes. Place drainage structures at all changes in pipe
size,pipe grade anddirection.
12.3.3.4.4
Roadside Open Channels
Base the geometry of roadside open channels (ditches) on the following:

Provide adequate design depth to day-light subsurface drains. The minimum depth from the PI to the
finished bottom elevation is 1.5 feet.

Design ditches with a standard 8 foot bottom width with rounded corners. Where site conditions
dictate, ditch bottom widths may be reduced to no less than 4 feet.

V-ditches are not allowed.
12.3.3.4.5
12.3.4
Retaining In-Place Drainage Structures
Reports/Plans
Submit a Project Drainage Overview Map to MnDOT for Acceptance prior to initiating detailed design and
submit a copy of the Project Drainage Overview Map in Microstation format. The Project Drainage
Overview Map serves as the base plan for final drainage design. Show the existing drainage features and
proposed Project drainage master plan, including drainage areas and contributing flows of existing and
proposed drainage. Show impacts from the Project and proposed mitigation within the map extents; and all
waters of the State, outstanding resource value waters, special waters, and impaired waters within 1 mile of
the Project that receive Project runoff.
Produce plans and specifications in a format that facilitates design review by MnDOT, according to Section
2. In addition to RFC plans, also submit the following documents:
 Drainage area maps showing each storm drain inlet with pertinent data, such as boundaries of the
drainage area for that inlet, topographic contours, runoff coefficients, times of concentration, and
land use with design curve number and design runoff coefficient.
 Location and tabulation of all existing and proposed pipe and drainage structures, including all pipe
and drainage structures proposed to be removed or left in place, out of service. These will include
size, class or gauge, catch basin spacing, detailed structure designs, and any special designs.
 Complete pipe profiles, including pipe size, type, and gradient, station offsets from the centerline
of the roadway, length of pipe, class/gauge of pipe, and numbered drainage structures with
coordinate locations and elevations.
 Drainage plan sheets showing the location of all stormwater ponds, infiltration basins, filtration
basins, and SPCDs and drainage features. If an existing structure or pipe/culvert was removed or
abandoned, it should be marked on the plans as such in red.
 Drainage calculations and all hydraulic models used to develop RFC plans. Provide all models
clearly matching the drainage area maps. Submit calculations as a pdf and in electronic format.
RFP
Drainage
12-5
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
Prepare a Drainage Design Report signed by a Minnesota-licensed Professional Engineer, which is a record
set of all drainage computations, both hydrologic and hydraulic, and all support data. Include all electronic
models, modeling files and the following within the Report:
 Hydraulic notes, models, and tabulations
 Storm sewer system designs
 Culvert designs and reports for major stream crossings
 Bridge and bridge culvert waterway design, models, waterway letter and risk assessment
 Pond designs, filtration designs, infiltration designs, structural pollution control device design,
including graphic display of treatment areas and detailed maintenance guidelines for operation
 Complete set of calculations and detailed drainage area maps detailing pre and post drainage
conditions, including electronic files
 Correspondence file
Prior to Final Acceptance, submit one hardcopy and one electronic copy of the Drainage Design Report.
Supply the report as a bound document and include all stormwater models organized by design topic.
12.4
Construction Requirements
12.4.1
General
Verify pond dimensions and depth within one month of Substantial Completion. Excavate to remove
sediment to meet design dimensions.
12.4.2
Construction Criteria
Maintain drainage to accommodate construction staging and provide drainage during all stages of
construction.
Obtain MnDOT Approval for abandonment methods for all existing drainage features that are being
abandoned with this Project.
Place reinforced concrete pipe under all roadways for storm sewers and culverts. Round pipe will be
gasketed (design 3006). Tie the following pipe joints:
 All joints on centerline culverts
 All joints to an outlet/inlet from the nearest manhole
 All bend sections and three joints on each side of bend
 Reducers, expanders and internal energy dissipation rings and three joints on each side
12.4.3
Materials/Testing Requirements
12.4.3.1 Infiltration Basins
Test the infiltration rate of each infiltration basin using a double ring infiltrometer prior to completion of the
basin. Conduct the test at the finished grade of the basin bottom, prior to blending the compost with the insitu soils or sand. Ensure infiltration rates meet or exceed greater of two times the designed infiltration rate or
2 inches per hour. Conduct a minimum of five tests per representative acre of basin area and a minimum of
five tests per basin. Conduct double ring infiltrometer tests in accordance with ASTM standards. Thoroughly
wet test areas prior to conducting infiltrometer tests.
12.4.3.2 Filtration Basins
Test all basins for filtration rates after completion. Conduct the test with a double ring infiltrometer and
ensure filtration rates meet or exceed 4 inches per hour. A minimum of five tests per representative acre of
basin area and a minimum of five tests per basin are required. Conduct double ring infiltrometer tests at the
RFP
Drainage
12-6
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
finished grade of the basin and in accordance with ASTM standards. Thoroughly wet test areas prior to
conducting infiltrometer tests.
12.4.3.3 Wet Stormwater Pond or Filtration Basin Liners
12.4.4
Instrumentation/Monitoring Plan
12.5
Deliverables

Preliminary Submittals



Project Drainage Overview Map (Microstation and Adobe PDF format)
Released for Construction Documents

Construction Drainage Plan Sheets and SWPPP sheets in accordance with MnDOT
Standard Plansheets

Construction Specifications

Drainage Design Supporting Information (see Reports/Plans section above)
Project Documentation

Drainage Design Report including all models and model files (one hardcopy and one
electronic copy)

HYDINFRA database as-builts

o
Deliver an inventory of the drainage infrastructure of the completed Project by
updating and uploading the MnDOT HYDINFRA database. Include information for
newly constructed, modified existing, and removed or abandoned drainage
infrastructure. HYDINFRA requirements are shown in Exhibit 12-D. Additional
information and resource files for meeting the requirements are available on the
MnDOT Bridge Office Website
(http://www.dot.state.mn.us/bridge/hydraulics/hydinfra.html). Contact the Project
Manager to obtain more information or training on the MnDOT HYDINFRA
database.
o
The drainage infrastructure inventory will not be considered complete until the data
is verified by MnDOT District Hydraulics or Water Resources Engineering MS4
staff. The verification process will include comparing plan sheets showing
constructed, removed, and abandoned drainage infrastructure to uploaded HydInfra
data. To expedite the process, it is advisable to send an email to both the MnDOT
Project Manager and the Hydraulic/Water Resources Engineering MS4 staff when
the data has been uploaded.
Infiltration and Filtration Basin Testing Results
o


Upon Substantial Completion, submit the results of tests for the infiltration and
filtration areas.
Notice of Termination (NOT)
Hydraulic Structures
 Risk Assessment and Hydraulics Recommendation Letter
RFP
Drainage
12-7
MnDOT Design-Build Program
Federal Project No. [insert #]
RFP
Drainage
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
12-8
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
MnDOT Design-Build Program
Federal Project No. [insert #]
EXHIBITS
All exhibits provided as electronic files.
Exhibit 12-A
Equipment/Software
Exhibit 12-B
Stormwater Storage Facility Design
Exhibit 12-C
Hydraulic Structures
Exhibit 12-D
HYDINFRA Requirements for Design-Build Projects
RFP
Drainage
12-9
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
MnDOT Design-Build Program
Federal Project No. [insert #]
EXHIBIT 12-A: Equipment/Software
Choose drainage design software from the following list:
Software
Possible Vendor
Functions
GEOPAK
Drainage
Bentley
 Rational method hydrology
 Inlet design and spread analysis
 Storm drain pipe design and hydraulic grade line analysis
Flowmaster
Bentley
 Inlet design and spread analysis
 Channel/pipe critical and normal depth, capacity
HydroCAD
HydroCAD
Software Solutions
LLC
 Generate NRCS (SCS) hydrograph
 Develop stage-storage and stage-discharge for ponds
 Combine/route hydrographs through ponds and channels
XP-SWMM
XP-Software
 Generate NRCS (SCS) hydrograph or model historical storm
 Dynamic routing of hydrographs through ponds, pipes, and
channels with varying tailwater/flow conditions
Hydraulic
Toolbox
FHWA
 Channel lining analysis
CulvertMaster
Bentley
 Analyze headwater and hydraulics for single or multiple
culverts and/or road overtopping
 Design pipe size based on maximum headwater
HY-8
FHWA
 Analyze headwater and hydraulics for single culvert,
multiple barrels, broken back culverts and/or road
overtopping
 Design pipe size based on maximum headwater
 Energy dissipater design
HEC-RAS
COE
 Water surface profiles for steady or unsteady flow
 Analysis of bridges, bridge-culverts, and culverts
P8 Urban
Catchment
Model
Walker
Model for predicting generation and transport of pollutants in
stormwater runoff in urban watersheds.
PEAKFQ
USGS
Gauge frequency analysis
SHSAM
BARR
Structural Pollution Control Device (SPCD) analysis
SMS
Aquaveo
2D hydraulic modeling for complex waterways using FESWMS
or TUTFLOW models.
RFP
Drainage
12-10
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
EXHIBIT 12-B: Stormwater Storage Facilities Design
Stormwater Storage Facilities
 Construct all stormwater storage facilities (wet ponds, infiltration basins, filtration basins and etc.)
with a minimum of 2 feet of vertical freeboard above the High Water Level (HWL) of a 100-year, 24hour storm event to the berm crest (continuous flat surface).
 Design all stormwater storage facilities with an emergency overflow to accommodate a 10-inch
rainfall event. Emergency overflows may consist of structures, overland channels and etc.
Permanently line all overland channels based on the flow produced during the 10-inch rainfall event.
Extend the lining from the crest of the berm on the interior side of the stormwater storage facility to a
minimum 5 feet beyond the toe of slope along the exterior edge of the stormwater storage facility.
Wet Stormwater Ponds
 Provide a minimum of depth from the NWL to the pond bottom of at least 3 feet and a maximum
depth of 10 feet.
 Provide a 1:10 (V:H) bench extending from the NWL 10 feet horizontally into the ponds, with other
slopes no steeper than 1:3 (V:H).
 Extend riprap for pipes discharging into the ponds to the pond bottom to prevent erosion.
 Provide submerged outlets at ponds to retain floating oils and other materials. Incorporate in the
outlet a combination of weirs and orifices to extend the detention time of runoff from low-intensity
events while passing peak flow from the design event.
 Dead storage beneath the outlet invert elevation for water quality ponds must meet the NURP and
watershed requirements.
Infiltration Basins
 Route rainfall runoff around the infiltration basin to the outfall during construction until all disturbed
tributary areas have been restored and turf within the infiltration basin is fully established.
 Provide an overflow to limit water depth in the infiltration basin such that the water elevation is above
the surface for no more than 48 hours.
 Base infiltration rates for the design of the infiltration basins on the MPCA Stormwater Manual
design infiltration rates. Do not use measured infiltration rates to design the infiltration basins.
Filtration Basins
 Base filtration rates for the design of the filtration basin on the MPCA Stormwater Manual design
infiltration rates. Base ponding depth within the filtration basin on the design infiltration rate and a
48-hour drawdown period.
RFP
Drainage
12-11
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
EXHIBIT 12-C: Hydraulic Structures
Culverts
A culvert is a hydraulic structure sized to convey surface water runoff under a highway, railroad, or other
embankment.

Minor culverts are 48 inches or less in diameter or span

Major culverts are greater than 48 inches in diameter or span and may include bridge culverts as
defined below
Bridges and Bridge Culverts
A hydraulic structure is classified as a bridge when the horizontal opening width of the structure is 10 feet or
greater measured along the roadway centerline, between undercopings of abutments, between spring line of
arches, or between extreme ends of openings for multiple boxes. The definition also includes multiple pipes
where the clear distance between openings is less than half of the smaller contiguous opening.
Ensure hydraulic computations, designs, and recommendations are consistent with past studies and projects
in the area by the COE, the DNR, and other State or Federal agency studies and projects.
Method Used to Estimate Flow for Culvert and Bridges
The following methods are listed in the preferred order for determining the design flow for culvert and bridge
structures. Ensure that the conditions in the watershed conform to the limitations of the selected hydrologic
method. For all methods, review available historical data and justify the design flow as meeting the local
Project conditions.
 For all crossings located within a FEMA Flood Insurance Study (FIS) with peak flow information,
use the flow information provided in the FIS and any subsequent Letters of Map Revision (LOMR).
 For a crossing on the same waterway as a stream gauging station with a length of record of at least 10
years, use the flow data available from the station to determine design flows within the limitations of
the MnDOT Drainage Manual and provided there is no major control structure between the gauge
and the design site. For analyses, follow the procedures in the Guidelines for Analyzing Flood
Frequency, Water Resources Council Bulletin 17B, 1982, and use the generalized skew coefficients
from Generalized Skew Coefficients for Flood-Frequency Analysis in Minnesota, 1997. Use the
USGS software package PEAKFQ for the gauge frequency analysis with the skew adjusted to values
from Generalized Skew Coefficients for Flood-Frequency Analysis in Minnesota, 1997.
 For crossings not located within a FEMA FIS or on a gauged waterway, select the appropriate method
for calculating the design flows from the MnDOT Drainage Manual based on Site conditions,
method limitations, and engineering judgment.
 For designs using the USGS Regression Equations, use Techniques for Estimating the Magnitude and
Frequency of Peak Flows on Small Streams in Minnesota Based on Data through Water Year 2005.
 For design sites where the local conditions require a hydrograph analysis, use the NRCS (SCS)
Runoff hydrograph procedures.
Culvert and Bridge Design Frequency
Design major culverts and bridges for a minimum of a 50-year frequency. Analyze the base flood (100-year)
and the lesser of the 500-year frequency or overtopping flood.

Analyze major culverts and bridges for the 2-year flood if there are fish passage concerns as part of
the DNR permit process. Guidance for fish passage can be found in Best Practices for Meeting DNR
General Public Waters Work Permit.
RFP
Drainage
12-12
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
Evaluate bridges for scour potential by using both the 100-year frequency flood and the lesser of the 500year or overtopping frequency. Report contraction scour, pier scour, and the final total scour depths for both
flooding events.
Design interstate highways, with a minimum overtopping flood based on the 100-year frequency.
Culvert and Bridge Hydraulic Analysis Methods
Use the Federal Highway Administration (FHWA) culvert analysis program, HY-8, HydroCad or
CulvertMaster for performing the hydraulic analyses at minor culvert crossings.
Use the Federal Highway Administration (FHWA) culvert analysis program, HY-8, or COE HEC-RAS
Water Surface Profile Program for performing the hydraulic analyses at major culvert crossings.
Use the United States Army Corps of Engineers (COE) HEC-RAS Water Surface Profile Program (current
released version) for performing the hydraulic analyses at bridge crossings, or use FESWMS or TUTFLOW
within the Surface Water Modeling Software (SMS) platform where appropriate.
Guidance for the use of 2-dimensional models is in HDS 7 – Hydraulic Design of Safe Bridges. If using a 2D
model, use FESWMS or TUTFLOW run in SMS.
Analyze bridge scour using HEC-18, Evaluating Scour at Bridges.
Evaluate piers in the 500-year floodplain for scour and design to be stable for the predicted scour. Design
pier stability without the dependence on countermeasures.
Design riprap at abutments in accordance with the procedures outlined in HEC-23. For bridge abutments in
urban areas or those frequently used by pedestrians, recommend alternatives to random riprap if applicable.
Culvert Design
For an existing crossing, design the new culvert so that it does not cause a greater headwater than the current
condition and meets the following criteria:

Design major culverts so the maximum allowable headwater elevation for the design frequency does
not exceed the shoulder PI elevation of the roadway low point.

Design minor culverts so the maximum allowable headwater elevation for the design frequency does
not exceed 1 foot below the shoulder PI elevation of the roadway low point.

Culvert extensions may increase the headwater elevation above the existing headwater elevation, but
not above the maximum allowable headwater.
Bridge and Bridge Culvert Waterway Design
Design bridge waterway to maintain the existing channel morphology through the structure, if possible. For
an existing crossing, design the new bridge or bridge culvert so that it does not cause a greater headwater
than the current condition.
If a bridge is over a commercial or recreational navigable waterway, follow US Coast Guard and DNR
requirements (whichever is applicable or most conservative) to provide sufficient clearance.
Submit hydrologic and hydraulic information and waterway design recommendations to MnDOT on the
Hydraulic Data form, with the appropriate information also shown on the bridge or grading plan. Definitions
for terms used in the Hydraulic Data form can be found in the MnDOT Drainage Manual and in the
following information:
Bridge Culverts
 Stage—Unconstricted water surface elevation just upstream of the culvert (i.e., natural conditions)
 Headwater—Constricted water surface elevation just upstream of the culvert (i.e., culvert existing or
culvert proposed)
RFP
Drainage
12-13
MnDOT Design-Build Program
Federal Project No. [insert #]
Book 2 – [insert full name of project] Design-Build Project
S.P. [insert #]
 Stage Increase—Difference in elevation between headwater and stage taken at the same location
Bridges
 Stage—Unconstricted water surface elevation sufficiently upstream of the bridge as to not affect
drawdown (i.e., natural conditions)
 Headwater—Constricted water surface elevation sufficiently upstream of the bridge (i.e., bridge
existing and bridge proposed)
 Stage Increase—Difference in elevation between headwater and stage taken at the same location
Bridge and Bridge Culvert Drainage Report
Prepare a report for the major stream crossings and include detailed calculations, in electronic and hardcopy
format, of the computer software input and output files, as well as a discussion of the hydrologic and
hydraulic analysis and reasons for the design recommendations. Include the following information for each
crossing:
 Hydrology
 Drainage area maps with watershed characteristics, hardcopy and ArcView shapefile (UTM
coordinates)
 Hydrologic calculations (where computer software is used, both hardcopy and electronic input
and output files)
 Historical or site data used to review computed flows
 Hydraulics and Recommended Waterway Opening and/or Structure
 Photographs of Site
 General plan, profile, and elevation of recommended waterway opening or structure
 Calculations—hardcopy of output, as well as electronic input and output files for all computer
models used for final analysis or for permit request, as well as summary of what the models are
 Cross-sections of waterway (hardcopy plot, plus any electronic data used. If GEOPAK or
ArcView TIN are used to develop cross-sections, include elevation model, as well as location of
cross-sections.)
 Profiles of channel
 Scour Analysis (for Bridges)
 Channel cross-section at bridge showing predicted scour
 Calculations and summary of calculations, clearly showing predicted scour and assumptions
regarding bridge opening and piers used to calculate predicted scour
 Discussion of review of long-term degradation/aggradation and effects
 Recommendation for abutment protection
 A MnDOT Scour Code for each bridge (Note the Scour Code in the Hydraulic Engineers
Recommendation box on the Bridge Survey Sheet.)
 Scour Analysis (for Retaining Walls)
 Recommendation for retaining wall protection
 Include report in the Drainage Design Report
RFP
Drainage
12-14