1 / 33

Hydrograph Reshaping for Hydromodification Control

This ongoing research project aims to solve the engineering challenge of hydromodification for clients, by developing an approach that reflects the timing and private development driven innovation. The project addresses the changes in watershed caused by urbanization and the subsequent alterations in rainfall-runoff response. It focuses on quantifying the changes and finding effective measures to fix the issues. The proposed solution involves sculpting the post-development hydrograph back into the shape of the pre-development hydrograph, using ponds and wetlands as storage and control structures. The project also explores innovative approaches such as latched outlet works and using a float mechanism for hydrograph matching. The research aims to provide a comprehensive and practical solution for managing hydromodification.

Télécharger la présentation

Hydrograph Reshaping for Hydromodification Control

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Ongoing Research • Skunk Works project • Started before hydromod was mainstream • Hydromod only • Engineering challenge to solve agency processing problem for clients • Approach reflects timing – private development driven • Idea conceived prior to agency response

  2. Development - Watershed Changes • Urbanization changes watershed physiography • Increased impervious area • Connected surfaces • Stormwater conveyance utilities • The watershed becomes a freeway for the excess surface water

  3. Hydromodification • Change in watershed rainfall-runoff response caused by alterations to watershed physiography • Reduced time to peak • Higher peak flows • Increased runoff volume • More frequent flow events

  4. Storm Response • Basin response to a storm (hydrograph) is altered

  5. Quantifying The Changes • Hydromod effects are cumulative over time • Commonly expressed as long term flow frequency diagram

  6. The Problem • Change to runoff pattern changes stream sediment transport and stream stability

  7. Fix It Attempts • MS4s in California have measures aimed at reducing hydromodification • General measures – low impact development • Specific measures – volume standards • Smaller projects are easier – set standards • Larger projects are harder – do a study • LID, LID, LID, LID, LID ...

  8. Development Approach 1

  9. Development Approach 2

  10. Property Owner Perspective • New MS4 requirements can be onerous • Retention takes space • LID can drive property use • LID implementation standard vague • Additional approval cycles • It is all new • No more studies please

  11. Middle Ground • Property owners are adjusting to new requirements • Development plans altered mid-stream • Uncertainty likely to persist even for properties at planning stages • Implementations may be awkward for now

  12. Hydrologic Wishful Thinking • Hydromod process is complicated on a regional scale • MS4 approaches seek to reverse or reduce physiographic changes to individual properties • Effect on watershed scale is not certain – probably better, but still modified

  13. Engineer’s Approach • Solve a problem for the client • Property development changes watershed subarea • Runoff hydrograph is altered • Restore original runoff hydrograph • Use off the shelf ideas • Catalytic converter for a property

  14. Hydrograph Plastic Surgery • Sculpt a post development hydrograph back into the shape of the pre development hydrograph

  15. Increased Runoff • Permanent storage is necessary

  16. Ponds and Wetlands • Ponds and Wetlands provide the basic structure for hydromod control

  17. Necessary Elements and Beneficial Features • Retention (volume control) • Detention (shape control) • Aesthetic feature • Structurally isolated • Water quality • Retrofit potential • Added value

  18. Storage Configuration • Pre Post hydrograph volume difference is stored • Sub invert storage chops off front of hydrograph

  19. Hydrograph Shaping Problem • Once front part of incoming hydrograph is stored problem is reduced to reshaping

  20. Hydrograph Reshaping – What We Know • At any time we know … • Incoming flow (chopped post development hydrograph) • Target outflow (pre development hydrograph) • Volume stored • Basin geometry (WSEL)

  21. Discretized Approach • Discretize pre development hydrograph (target points) • Match pre development storage and flowrate (outflow) at target points

  22. Outlet Works Driven

  23. Pond/Wetland Tuning • Outlet works is adjusted to match pre development flow at each target point • Rows of orifices added at each target WSEL to adjust total pond outflow • Orifices not mandatory – may use weirs • Tuning approach works great provided that pre development hydrograph is rising

  24. Going Up Is Easy • Pond volume (WSEL) is increasing • Pre development flow is increasing • Add more orifices

  25. Engineering Decision Point • Match pre development hydrograph on the way up • Cross our fingers on the way down • Examine cumulative process • Normal approach

  26. Normal Approach • Regard Pond or Wetland as treatment control • Tune pond or wetland for fundamental storm • High frequency event • Stream changing effects • Adjust to obtain desired long term results • Continuous simulation

  27. Out of The Box Approach (Research) • Seek to continue hydrograph sculpting on falling limb of pre development hydrograph • Requires additional design element • Idea conceived for wetlands diversion project

  28. Latched Outlet Works • Use a float mechanism to activate flapgate • Open up or close off a portion of the outlet works • Alter outlet works configuration • Contour hydrograph on falling limb • Hydrograph matching • Agency approval may take work initially

  29. Hydrograph Matching • Discretized approach (target points) allows the discharge from the pond or wetland to closely match pre development hydrograph • Moot point since hydrograph is matched for the fundamental storm • Cumulative effects, long term simulation, and tuning is still required

  30. Numerical Process • Unit hydrograph convolution • R1 = U1 *P1 • R2 = U2*P1 + U1*P2 • R3 = … • Pond WSEL and pond geometry provide means to predict pre existing outflow for any storm

  31. Hydrologic Undo • Pond configuration maps incoming flow to project watershed precipitation pattern • Pre development unit hydrograph is used to convert rain pattern to pre existing runoff which provides target outflow • Goal is to convert post development project to pre development hydrology at the D/S end

  32. Future World • Goal is to match hydrographs for any storm • Eliminate hydromod • Ultra low impact development • Agency rubber stamp • Everyone happy

More Related