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Flood control and River Engineering

  • 1.  Flood control and River Engineering

    Posted 12-27-2021 01:35 PM
    How we can control floods? What are the mechanisms to control flash floods?

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 2.  RE: Flood control and River Engineering

    Posted 12-29-2021 09:35 AM
    We can either try to limit the amounts of rainfall/precipitation becoming runoff or try to slow the runoff as much as possible.
    This is the list that I can think of
    • Increase forest cover
    • Increase permeable surface e.g., green space, pervious concrete/asphalt 
    • Collect rain from roofs (green roofs)  
    • Build Infiltration wells & basins, retention & detention basins, reservoirs & dams to store and regulate excess flow.


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    Tung Nguyen, PhD, Water Resources Modeler
    Jacobs
    Sacramento, CA
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  • 3.  RE: Flood control and River Engineering

    Posted 01-03-2022 09:02 AM
    Good morning and hopefuly a better 2022 than 2021. One other way to reduce flooding is changing the design discharge volume to be drained at the peak of the event. Namely, in many places the maximum discharge is based on events with an average return period of once in 100 years. However, if we talk about large drainage systems or rivers of temporary detention ponds, which are expected to operate 50 or 100 years without flooding. the economical life time of the system (50, 100 years) is an additional impartant parameter. It can be shown easily that for an average return period of 100 years and a economical life time of 100 years, there is a risk of 63% that larger volume events will occur during the 100 years period. A low risk should be chosen of say only 1% risk of a larger discharge to occur during the 100 years. This leads to choosing the limiting design event to one with an average return period of once in 10,000 years (such as adopted in the Netherlands). Certainly this means designing for larger cross sections of the drainage system/s and basins. The relationship between the risk r, the average return period for design T (years) and the economical life time L (years) is given by the formula:
    T= 1 / (1 - (1 - r) **(1 / L) )  where ** means: at power. In this way one can decide to which risk % he designs the drainage system.
    Furthermore, one should take account of the impact of climate change with more frequent extreme events and increased sea levels within the next 30 and 80 years, which will affect the flow gradients (reduce) for systemms draining to the sea/ocean. The assessment needs to account for extreme events acounting for the climate change induced discharges/precipitation volumes due to a non stationary climate and the dificulty of assessing discharges for so large return periods. Furthermore, one needs to account for the related damages associated with extreme events of various return periods, before the final decision to what return period a drainage system needs to be designed.

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    Dov Rosen P.E., M.ASCE
    Sergiu Dov Rosen Sea Shore Rosen Engineering Consultants
    Haifa
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  • 4.  RE: Flood control and River Engineering

    Posted 02-06-2022 01:32 PM
    Hello Dov, Thank you for your response and recommendations!

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 5.  RE: Flood control and River Engineering

    Posted 02-06-2022 01:32 PM
    Hi Tung, Thank you for your response and reccommendations!

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 6.  RE: Flood control and River Engineering

    Posted 01-03-2022 11:54 AM
    Floods are only a problem if they result in flood damage or increased risks to the health and safety of the public.  Flood damage of concern is primarily damage to infrastructure and environmental damage as a consequence of flooded development.  Past development practices have included encroachment within floodplains and construction of flood protection works to mitigate potential flood damage.  This past practice is not a particularly sustainable model in the long run, at least not without considerable ongoing investment.  Prudent development practices today include avoiding development in floodplains and considering new development in a manner that will not aggravate floods.  Along rivers presently confined by levees adjacent to the active channel, the levees may be set back from the channel to allow more flood storage adjacent to the river thus reducing downstream flood peak flows.

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    Norman S. Braithwaite, P.E. M.ASCE
    President, Pacific Hydrologic Incorporated
    www.flood.pro
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    Norman Braithwaite P.E., M.ASCE
    Consultant
    Redding CA
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  • 7.  RE: Flood control and River Engineering

    Posted 02-03-2022 02:57 PM
    Hello Norman, Thank you for your response and recommendations! Yes, it is a current issue

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 8.  RE: Flood control and River Engineering

    Posted 01-03-2022 02:37 PM
    Five points to consider for a more rational mitigation of flood risk:
    First and foremost, decisions will vastly improve when we define AND MAKE WIDELY AVAILABLE the specific Expected Annual Cost and Present Value ($) of flood risk for every floodplain property.  This is becoming increasingly easier with high resolution data/analytics/modeling.  (In the US, the NFIP Risk Rating 2.0 is a very limited step that does not take full advantage of today's flood risk pricing technology and continues to substantially under- and over-price a lot of flood risk.)  Note PV must incorporate reasonable estimates of future climate and landscape change.  Every property-stakeholder should be encouraged to recognize their own responsibility for due diligence (i.e., understanding the PV of their flood risk and its impact on their property value), insuring, and mitigating their property-specific flood risk--as with all hazards!

    Second, the very definition resiliency and sustainability of any asset/property/community for flood risk means that all the necessary resources are available for timely and comprehensive recovery WHEN--NOT IF--flood damage occurs.  If an asset/property/community is subject to substantial damage and not being restored during its intended design life, then it isn't really resilient or sustainable.  So there must be some sound private/public/public-private method of financing flood recovery.  Potential methods include commercial insurance/reinsurance markets; government oversight; government-run insurance programs, public-private partnerships; post-disaster aid, etc.  It is pretty clear that for just about any reasonably well-defined property-specific financial risk, well-regulated commercial insurance/reinsurance markets tend to provide an effective, efficient, and unbiased way to finance that financial risk.

    Third, community officials should identify public mitigation and regulatory alternatives that might legitimately reduce aggregate EAC/PV--i.e., the collective cost of financing flood recovery; then determine the cost of implementing and maintaining the alternatives.  This cost must include costs of preventing any adverse flood, environmental, economic, and social impacts.  The officials can then pursue and optimize any reasonable measure that effectively reduces the aggregate cost of financing flood risk.  Community officials should be very careful when it comes to mixing the objective of mitigating flood risk versus other public goals--such as environmental restoration and protection, development aesthetics, recreation, water supply, hydropower, etc.  Dollars marked for flood risk reduction investment should only go to measures that will demonstrably reduce the PV of flood damages.

    Fourth, ideally in most cases, those community property-stakeholders receiving the PV benefits of public flood risk mitigation should be the ones to largely pay for the mitigation; subsidizing and distorting flood risk should be avoided.

    Fifth, where there has been past systemic discrimination in property ownership, governments should pursue measures to remedy unequitable distribution of flood financial risk.  But in providing such measures governments should not continue to subsidize/distort flood risk.

    Given the current variable state of technology and political commitment to rational flood risk mitigation, following these points presents more of a challenge in some communities (and parts of the world) than in others.

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    Robert Jacobsen P.E., M.ASCE
    President
    Baton Rouge LA
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  • 9.  RE: Flood control and River Engineering

    Posted 02-03-2022 02:57 PM
    Hello Robert, Thank you for your response and brief recommendations!

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 10.  RE: Flood control and River Engineering

    Posted 01-03-2022 03:06 PM
    We can't control floods, but we can manage risk.  In reference to good observations in comments others have posted, there are things we can do to incrementally reduce peak flows, but these reductions probably will not meaningfully reduce the large flood events we are experiencing globally.  The nature of the precipitation input has changed, and what we are learning from that change needs to be incorporated in how we plan for future events.  Mr. Braithwhite is describing perhaps the best approach in trying to not put people and infrastructure in harms way, or making space for the hazard as much as possible.  Perhaps the question we need to answer is what will we do differently as engineers, property owners, dam operators, leveed communities, etc. to minimize risk into the future.

    Terry R. Zien, P.E., CFM

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    Terry Zien P.E., M.ASCE
    Hydraulic Engineer
    US Army Corps of Engrs
    Mendota Hts MN
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  • 11.  RE: Flood control and River Engineering

    Posted 02-02-2022 04:05 PM
    Hello Terry, Thank you for your response and recommendations! you also focused on I hope Mr. Mr. Braithwhite described approaches. ofcourse the main question is what we will do differently as engineers?

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 12.  RE: Flood control and River Engineering

    Posted 01-04-2022 04:25 PM
    I recently wrote a paper on reducing urban flooding using localized retrofit solutions. There is a lot of potential for reducing urban flooding risk by the implementation of low-impact development (LID) designs such as rain gardens, green roofs, pervious pavement, etc.
    There's quite a bit of data out there on case studies regarding LID and urban flooding. If you'd like to be pointed to specific resources, let me know.

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    Heidi C. Wallace, P.E., M.ASCE
    Tulsa, OK
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  • 13.  RE: Flood control and River Engineering

    Posted 02-02-2022 04:05 PM
    Hello Heidi, Thank you for your response and recommendations! we are waiting for your new paper!

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 14.  RE: Flood control and River Engineering

    Posted 02-03-2022 02:26 PM
      |   view attached
    I have attached my paper on Retrofit Solutions to Reduce Urban Flooding and Related Negative Impacts for your reference

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    Heidi C. Wallace, P.E., M.ASCE
    Tulsa, OK
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  • 15.  RE: Flood control and River Engineering

    Posted 01-10-2022 09:33 AM
    Do we want to control floods or minimize damage?  The national flood insurance program was supposed to help minimizing damage by restricting development in flood prone areas.  However, it also offered low cost insurance to those structures already built in those areas.  We continue to see payments to these owners after multiple flood events.  Coastal areas which are mostly vacation homes are an excellent example.  How many times does the owner get to claim damages?  After a couple of events, maybe it would be better to just buyout the structure and prevent further development in that location.  Yes it is a radical sounding concept, but flooding is a naturally occurring event that has little potential to be controlled without massive investment.  Maybe the answer lies with more common sense approach.

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    Barry Nelson, LG, Aff. Member ASCE
    Chief Hydrologist
    Northwest Geoscience, PC
    High Point, NC
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  • 16.  RE: Flood control and River Engineering

    Posted 02-02-2022 04:05 PM
    Hello Berry, Thank you for your response and recommendations! Yes, it needs a massive investment to control flood!

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    Ebissa Gadissa S.M.ASCE
    PhD Scholar
    Addis Ababa
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  • 17.  RE: Flood control and River Engineering

    Posted 02-03-2022 02:26 PM
    To reiterate--the first, most critical, and I think the most cost-effective investment required is to provide every property-stakeholder with the actual numbers that represent property-specific flood financial risk:  the Expected Annual Cost and Present Value.  Just think of how much easier and more effective government efforts will be when they can be leveraged off of improved responsibility on the part of property-stakeholders for their own flood risk due diligence, insurance, and mitigation.  As you may know, Flood Factor is now promoting a crude rating from 1-10, and NFIP Risk Rating 2.0 is making some limited strides toward the real property-specific actuarial cost of flooding.  These are obviously pointing us in the right direction.  Fortunately, today's technology allows us to do much, much better.

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    Robert Jacobsen P.E., M.ASCE
    President Bob Jacobsen PE, LLC
    Baton Rouge LA
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  • 18.  RE: Flood control and River Engineering

    Posted 01-20-2022 07:43 PM

    If I remember correctly, we have discussed facets of this issue under different headings previously. It is an important one during the time of the effects of warming climate with all the associated instabilities and extremes. There are several NAP publications dealing with the science and engineering of flood problems, remedies/protections, risks and effects, see, for example 1995 NAP 4969 and 2012 NAP 13393.

    There are many others – one can always check in: Hydraulic Design of Flood Control Channels, USACE EM 1110-2-1601; Hydrologic Frequency Analysis, USACE EM 1110-2-1415; and Design and Construction of Levees, USACE EM 1110-2-1913. In my article Flood Barrier Systems, I have attempted to look into it from a broader perspective – but focusing primarily on Storm Surge Barriers. Different aspects of Water Actions that warrant protection were identified – together with discussing the Flood Barrier Hydraulics. They were followed by highlighting some major Storm Surge Barriers around the world.

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    Dilip

    Website

    ORCID ID

    Google Scholar



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    Dr. Dilip Barua, Ph.D, P.Eng, M. ASCE
    Vancouver, BC, Canada
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  • 19.  RE: Flood control and River Engineering

    Posted 27 days ago
    I was in a group that worked on this regarding controlling flash floods around a building we were designing.

    Two members constructed a basin design with ten pipes and basins for said pipes with a perimeter around the building, using underground slopes and elevation to direct rainfall into a specific direction away from the building. During that process, I researched what the highest precipitations were for 25 and 50-year storms within the city. Using flow rate equations I learned in one of my classes, an excel sheet, and those results, I determined what the diameters needed to be for each individual pipe so that they could handle that much rain; the design involved pipes gradually pouring their rain into one final pipe, which we accounted for in the excel sheet.

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    Alexander Granato A.M.ASCE
    Student
    Bexley OH
    granato.3@...
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