Hydraulic Culvert Design and HY-8 Purdue Road School March 9, 2011

INDOT Office of Hydraulics Your Presenters: Crystal Weaver, PE John Bartolo, PE INDOT Office of Hydraulics

HY-8 Basics Culvert design software from Federal Highway Administration (FHWA) Shareware available from FHWA Based on “Hydraulics Design Series 5: Hydraulic Design of Highway Culverts” (HDS 5).

Win HY-8 Supersedes HY-8 6.2 First released as HY-8 7.0 beta First public release as HY-8 7.1 HY-8 6.2 is the DOS version, dating back to 1987. HY-8 7.1 was publicly released in July 2008.

Win HY-8 vs. DOS HY-8 No longer DOS based Input data is Excel friendly Output available as a Word document or PDF While no longer DOS based, the program retains the same data inputs and design concepts. Input data can be copied from or to Excel directly from HY-8. Word Document is in rich text format.

Win HY-8 vs. DOS HY-8 Fixes some long standing bugs Allows import of DOS HY-8 files Adds new functionalities Bugs fixed: The top and side n value vs. bottom n value issue. Can revisit old projects, in new program. New functionality – embedment (sumping), pre-defined arch boxes (Conspan) now available. More on next page.

Win HY-8 New Functionality Multiple culverts allowed in each run Multiple culvert options in one project file More functionality coming as funding allows Previously, could only “twin” structures. Now can add multiple shapes, for culvert rehabilitations (i.e. jacking a pipe), critter crossings, etc. Can place all design options – original plus multiple proposed, etc in one file.

Win HY-8 Data Input Main input screen – all data will be input here. In two main sections – left hand side is location specific, and had Discharge, Tailwater (downstream cross section), and Roadway Data. Right hand side is culvert specific – the culvert shape, Manning’s roughness, inlet conditions, and site data. The blue question marks open the program Help to that specific topic. Crossing name – you will make your own naming convention as you go, but I recommend something along the lines of “Existing” or “Proposed” or other identifying characteristics. In background, on the left side, is the Project Explorer – it works like a Windows tree. Use this to run all options in one file. The Project is the full file. The Crossing is the individual model. The Culvert is the individual structure. If you have twinned structures, there will be two culverts in the crossing. If you want to run an existing and a proposed model, there will be two crossings in the Project.

Win HY-8 Data Input Minimum Flow should be 0 cfs Design Flow and Maximum flow are usually Q100 Can run multiple flow rates, if using other design storms Example – if AADT requires Q25 serviceability, you can place the Q25 flow rate in the design flow rate, and Q100 in the maximum flow rate, to check serviceability and backwater in the same run.

Win HY-8 Data Input Six options for tailwater shape Pick the appropriate shape for the circumstance Enter slope, n values, and appropriate data Will be running Irregular shape for this explanation. Trapezoidal and Triangular – good for roadside ditches & dredged ditches Irregular best for natural channels Rating Curve good when another structure is immediately downstream, and will backwater into your structure. Constant tailwater good if there’s ponding, no real channel, etc.

Win HY-8 Data Input Irregular tailwater entered here Can import tailwater from older models Requires x & y coordinates, and Manning’s n value The tailwater cross section should be cut approximately 15 ft downstream of the structure. This ensures the cross section is representative of the natural channel, outside of any scour holes or other effects of the culvert or road. HY-8 assumes the flow line of the channel matches the outlet elevation of the structure. You may have to propagate the cross section upstream to get the elevations to match. Additional finagling will be needed if embedment is being used.

Win HY-8 Data Input Each segment of irregular channel gets an n value. n value entered at Point 1 is for segment between 1 & 2 And so on… No n value entered for last point in tailwater

Win HY-8 Data Input Two options for roadway data: Constant Elevation Irregular Two options for roadway surface: Paved Gravel Input discharge coefficient An irregular shape can be input as well. This is ideal when plans with a profile grade is available, especially if the PG is not flat. The irregular shape is entered just like the irregular tailwater. Crest length is flow width across the road. Top width is actual width of road Input coefficient is for other surfaces – have used it for a timber deck. Not a commonly used option.

Win HY-8 Data Input Many options available for culvert shape Several inlet types and edge conditions too Culvert shapes: Circular, Pipe Arch, Elliptical, Box Culverts, User Defined, Arch-Boxes (Conspan), etc INDOT has not approved Arch, Open Bottom, High or Low Profile Arches. INDOT generally doesn’t use metal boxes; however, local jurisdictions do. Embedment is entered here, in inches! In 7.2.4, the program will adjust the structure inverts to account for the embedment. In 7.1, you have to do it yourself. Manning’s n is entered for you, depending on the material type. You can adjust it if you need to. If the embedment or user defined options are used, two n values fields will appear – one for top and sides, and one for the bottom. A variety of inlet edge conditions are available. For pipes, projecting or headwalls are the most common. For box culverts, wingwalls are preferred on INDOT projects. The inlet depression is usually No. They are used rarely – to prevent erosion from cutting upstream of a structure, when the upstream is just a broad swale, and to reduce the structure slope (and velocity), if there is a large difference between the upstream and downstream.

Win HY-8 Data Input Two options to input data Stationing is relative Culvert Invert Data is the easiest to use. Stationing is relative Can use known stations from plans, if available Just need invert elevations. Can use relative elevations, if actual survey is not available. That is being done here. Can use relative or actual stationing too. In this case, just set inlet at 0, and outlet at the structure length. The program assumes the outlet elevation matches the tailwater flow line. Sometimes elevations need to be adjusted. Can twin a structure here too – just change the number of barrels, or use the duplicate culvert button at the top of the screen. (Show on next slide.)

Win HY-8 Data Input Once Data is entered, Analyze Crossing

Win HY-8 Results What results do we need? Backwater depth Outlet velocity Roadway overtopping Appropriate water surface elevations Freeboard is only really needed on concrete boxes and three sided structures.

Win HY-8 Results What is backwater? The difference between the upstream depth and the downstream depth, at the culvert. Caused by a constriction in the channel, such as a culvert.

Win HY-8 Results First page is the Crossing Summary Table Displays Headwater Elevation, Total, Culvert, and Roadway discharges Cuts flow into 10% intervals from minimum flow (0 cfs) to maximum flow (Q100 – 100 cfs), and shows how the culvert acts at each level. Can see where road overtopping begins to occur – in this case, it is happening after the Q25 (75 cfs), but before Q100. Iterations on the right side show how long it takes the program to balance the flows between the culvert and the roadway.

Win HY-8 Results Second page is the Culvert Summary Table Displays the bulk of the data. Cuts flow into 10% intervals from minimum flow (0 cfs) to maximum flow (Q100 – 100 cfs), and shows how the culvert acts at each level. Gives headwater elevation, inlet and outlet control depths, flow type, normal, critical, outlet, and tailwater depths, outlet and tailwater velocities. Calculate backwater from this table: Headwater Elevation – Inlet Elevation = (in this case) outlet control depth. Whichever controls is bolded. Outlet Control Depth – Tailwater Depth = Backwater. In this case, backwater is 1.31 ft. Does not meet INDOT standard – will have to upsize the culvert a little. Can see data for Q25 and Q100 here. Can see that no overtopping is occurring at Q25 (total discharge and culvert discharge match). Get Q25 velocity at the outlet velocity column. Here it’s 6.32 ft/s – revetment riprap required. 100 year water surface elevation = tailwater depth + outlet elevation. In this case, since outlet elevation is relative, I would just give the tailwater depth. If actual survey is performed, the designer can add the tailwater depth to the surveyed outlet elevation to get the water surface elevation.

Win HY-8 Results Report options available Select Create Report from Culvert menu Report Generator appears Report Generator allows options Select output format Select data to be reported Reports can be exported as a Word Document (rich text format) or PDF. Can select type of report – standard, summary, or custom. Can add or remove tables and charts at the bottom. Report will open in the appropriate program and can be saved from there. One problem with RTF report – all tables automatically dock at the top of a page. Has to be condensed by hand, if you don’t want the report to take up 7 pages. The summary report generally can be reduced to ~3 pages. This is a known problem, and FHWA has not yet found a solution.

Win HY-8 Tips & Tricks Profile view available Shows sumping, water surface elevations upstream, downstream, and through structure Select the Culvert in the Project Explorer on the left.

Win HY-8 Tips & Tricks Front view also available Looks through the structure. Select the Crossing in the Project Explorer to the left Will have to define the structure stationing To define the structure stationing, right click in the middle of the screen and select “Define Roadway Culvert Stations”. I usually just set the culvert station for the midpoint of the road, unless I have plan data otherwise. If this is not done, an error will be present. This does not affect the hydraulic model.

Win HY-8 Tips & Tricks Can run multiple models in one file Right click on Crossing in Project Explorer, select Duplicate Copies all input data, so only the structure needs to be changed. Do not duplicate the Culvert – this will twin the structure. Can run as many options as needed – have successfully run 10+ options in one model. Naming conventions become important!

Win HY-8 Tips & Tricks Crossing correctly duplicated Ready for any changes to be made to the structure

Questions? Crystal Weaver cmweaver@indot.in.gov (317) 233-2096 John Bartolo jbartolo@indot.in.gov (317) 232-5228