The HEC-RAS Model Refresher

Transcription

1 The HEC-RAS Model Refresher Minmin Shu P.E. Transportation Review Unit Water Resources Division Michigan Department of Environmental Quality

2 What Does the HEC-RAS Mean RAS----River Analysis System HEC----Hydrologic engineering Center of U.S. Army Corps of Engineers

3 What Kind Analysis the HEC-RAS Can Do Steady flow water surface profiles (one dimensional) Unsteady flow simulation (one or two dimensional) Sediment transport/movable boundary computations Water quality/water temperature analysis modeling

4 Which Part of HEC-RAS Software We Use Most in the Hydraulic Analysis for Obtaining the Part 31 Permit 1. Steady flow analysis(one dimensional) ---- for most cases 2. Unsteady flow simulation (one dimensional)

5 Steady Flow Analysis (one dimensional) We use energy grade line elevations (EGLE) instead of water surface elevations in Part 31 review. We focus on the EGLEs comparison of existing and proposed condition to decide if the proposed condition has equal or greater hydraulic capacity and no harmful interference. The modeling that we required does not mainly focus to find the precise floodplain elevation, but if there is FEMA detail study near or at the proposed site, the FEMA floodplain elevation should be considered as the boundary condition of the flow file in your model. The other conditions.

6 Unsteady Flow Simulation (one dimensional) If the flow wave is dynamic: The discharge will vary in space and time, attenuating as it moves Downstream. The calculated discharge-stage ratings will not be unique. In practice if there is a dam, retention/detention pond, lake or other storage area, unsteady flow simulation may be considered.

7 A Simple RAS model Project title - Project file (.prj) Geometric data Geometry file (.g01, ) Design flow - Flow file (f01, )

8 Create a Project and Save it---.prj

9 Geometry file River Reach Cross Section Bridge/Culvert Inline Structure Lateral Structure..

10

11 Direction Basic Rules for Geometry File Draw the river reach from upstream to downstream Looking downstream, input the cross sections, road profile and structures from left to right. Length of the model (Reach Length) Minimum length from upstream of contraction starting to downstream of the expansion ending. If there is backwater..? Number of the Stream Cross Sections 4 are the minimum numbers of the stream cross sections, 2 on upstream and 2 on downstream of the road.

12 Ineffective Flow Area

13 A part of the cross section area that contains water which is not actively being conveyed (velocity is near or equal to zero).

14 Select Ineffective Mode 1. Normal ineffective flow area. 2. Multiple blocks without/with check Permanent option.

15 Station & Elevation Setting 1. Station: Ratio of 1 to 1 on upstream and 2 to 1 on downstream; by program default or by site inspection result. 2. Elevation: Low point of the road if it is within the stream floodplain.

16 Please Remember--- When using ineffective flow areas, no additional wetted perimeter is added to the active flow area. Ineffective flow area vs. obstructions Obstruction permanent blocked out a part of cross section area and add the wetted perimeter when the water comes in contact with it.

17 Contraction and Expansion Coefficient

18 Contraction and expansion coefficients are to evaluate the amount of energy loss that occurs because of a flow contraction or expansion

19 The difference of setting on the energy only vs. Pressure and/or weir

20 If the Bridge Has Piers

21

22

23 Geometry File Issues 1. Should they be included If there are other structures within or near the studied river reach? 2. How to modify If the EGLEs of the proposed condition are higher than that of existing condition? 3. How to test if the last downstream cross section is far enough?

24 Flow file Flow values Flow change locations Flow boundary conditions

25 Flows & Locations Q cfs from RS 2846 to upstream of RS Flow starting at RS 1596 will cover the stream to end of model.

26 Flow Boundary Conditions Select option of set boundary of one profile at a time, high light the Downstream of the target flow and make the change.

27 How to Establish a RAS Model Quick Design flow, site survey data and design of proposed condition on hand Import data electronically

28 Import Data Through the HEC-RAS From HEC-RAS main window, under File, select Import HEC-RAS Data, any HEC-RAS format file could be imported. From HEC-RAS Geometric Data window, under File, select Import Geometry Date, only geometry file can be imported, you have the options to select whole geometry file or some items in a geometry file.

29 Simulating Each Plan 3 flow regimes Set flow distribution

30 Read the Results Stand table User defined table

31 In above red circle, click on the left button or right button, different stand tables will open.

32 In above red circle, click on the left button open the Cross Section Output, under Type there are many other stand tables

33 Click on the right button, open the Profile Output Table. Under the Options there is a list of the stand tables. Under Options you could select to include different information in profile table.

34 Still under Options you could select Define Table, and create Table Heading and save it as a special table, it will be kept under User Tables, it can be used when you run other projects.

35 Read the Figures Profiles Cross sections others

36 Profile Plot

37 Cross Section

38 3-D View

39 Refine the Model Based on If the Results Show an Issue Read the Errors Warnings and Notes Adjust the model settings Adjust the proposed design

40 If You Still Have Unsolved Issues We are here to assist, please your model and support data to the Transportation Unit s engineers: Linda Hansen P.E., HansenL6@michigan.gov Ashely Roznowski P.E., RoznowskiA@michigan.gov Minmin Shu P.E., SHUM@michigan.gov Jim Watling, P.E. Supervisor. WATLINGJ@michigan.gov