Hello Ladies and Gentlemen:
How is the going?
You might have noticed that I haven’t been on this blog for sometime. But am back! Well may be recession might have played a role! Just kidding am doing just fine :) to quote Suze Orman the Internationally Acclaimed Personal Finance Advisor.
Anyways I have to apologize in advance coz I know I will surely be in trouble on this post, I will get some phone calls asking me to explain why on earth I can decided to write on a topic that is purely technical than on a general life experience or episode that we can all exchange ideas and contribute to, and I totally get it. To be sincere I didn’t want to, but you know I love design and at the moment not doing much of it momentarily so it’s a natural inclination for me to read a little bit just to stay current with that stuff especially on Hydrology and Hydraulics (the two most misunderstood terms even by practitioners’ themselves, but that is a whole different story).
Anyways, here we go just read as an entertainment or some novel for fun! Am sure most of you will make sense out of it, after all its English, I didn’t write it in Swahili! Some of you are going what is that? It’s a Kenyan National Language, Just like English in US!
Shifts in focus from Peak Flows Based Hydrology (PFBH) to Volume-Based Hydrology (VBH).
To start, Andrew J. Reese a vice president with AMEC Earth & Environmental Inc. quoted General George Patton famous statement “If everybody is thinking alike then somebody isn’t thinking” – you know the amazing thing that I like about this quote is that its plainly true that its counterintuitive if we all be thinking alike, this world will be boring, we will not have all the break-through that have led to industrialization age as well as advancement in technology that has immensely improved our human living conditions. Someone had to think “outside the box” to use this infamous cliché.
Anyways back to the PFBH vs. VBH. Just to give a preview of what shifts have been made in Urban Stormwater "Practitioning", Let see Sixty years ago, efficient drainage was the way to do things, using separate stormwater systems of pipes. Forty years ago, efficient drainage was causing flooding problems and switched to a detention design standard. Twenty years ago, detention ponds were failing for a number of reasons and switched to a more comprehensive master planning approach—that is, those who could afford all that modeling, understand its output, and had the wherewithal to actually construct regional systems for stormwater treatment to para phrase Mr. Reese. In the ensuing 20 years, there has been a rapid diversification of stormwater design from a simple consideration of flooding and conveyance to channel erosion, stormwater pollution, groundwater recharge, and natural approaches to stormwater design.
All these past approaches to urban stormwater hydrology focused on peak flow (and flooding) and, secondarily, on velocity. Basically Peak flow was and is still key until we shift gears, the ultimate stormwater controls structures’ sizing factor (for the most part). But as we start to focus on stormwater quality, there was a recognition that we were treating volumes of runoff because we were most often trying to reduce quantities or concentrations of (versus flow of) pollution. This often led to a sort of “Frankenstein-ian,” cobbled-together approach to stormwater design where a water-quality volume is treated, but the rest of the design was still all about peak flow.
The most recent on this subject in an attempt to shift to VBH rather than PFBH is the 2007 Energy Independence and Security Act (Section 438) deals with redevelopment or new development on federal facilities, stating they must seek to maintain predevelopment hydrology with respect to temperature, flow rate, volume, and flow duration. EPA’s CSO control policy “presumptive” approach has a volume-elimination option, which has led to, among other things, a green infrastructure emphasis. This for most stormwater practitioners is a green light towards VBH.
VBH has a comprehensive stormwater management approach that focus on 5 objectives.
1. Infiltrated Flows – the Initial rainfall depth to capture as initial abstraction or infiltrate into the ground (re-charge ground water). On the other hand though we have to be careful when doing this since the law of unintended consequences (Murphy’s first cousin) has it that all this infiltration in an urban area can be problematic in the future just be cautious!
2. Most Populated Flows – basically as the rainfall begins to intensify the flow begins to mobilize sediments and pollutants and it makes all sense if we have to achieve removal of high % pollution then we need to capture and treat this so called “first flush”.
3. Most Erosive Flows – basically this is about somewhere btwn ¾ to bank full as the rainfall intensifies. As its well know that sediment is transported when the shear force in flowing water exceeds the ability of the bank and bed materials to withstand the shear force. This shear stress moves sediments downstream, pulling on bed and banks; this is usually causes scouring effect to the river banks as well as beds.
4. Most destructive Flows. - Basically as the rainfall intensifies, the ability to infiltrate becomes problematic and overall volumes increases, the flows and velocity becomes violent and can be destructive. So here is where we start thinking to delay or manage excess volumes that may be over-capacity of our onsite detention / retention structures.
5. Biggest flows to consider – 100-yr storm for the most part is considered the biggest and here we tend to focus on safely passing the flow.
I hope I convinced you guys that VBH is more compressive that PFBH.
So anyways, to rationalize it my point is that “If everybody is thinking alike then somebody isn’t thinking” ( to go back to General George Patton). I think it makes a big different if we be forward thinking that just getting stuck in one old idea be PFBH or some old and tired Health System, and that is why i kind like the "dialogue" about Health care reforms atleast someone has a different opinion, that good enough!. We should be always open to change not scared to death by change, otherwise if Sir. Issac Newton (1643)didn’t out curiosity asked himself the question that no one else before him asked himself then all modern Physics including the Law of Gravity, by the way which hydrology is based on will not have been discovered.
Its mind blowing to Imagine that sixteen hundred and fourty three (1643) years before Him No else ever asked themselves the very question that Sir. Issac Newton asked himself that led to his "discovery" of the Laws of motion and later be known as the Father of Physics. Isn't that Incrediable? Given that other before him had somewhat tried to (including the Astronomer Johannes Kepler who discovered Laws of Planery motion 1571-1630) but with still controversies till Sir. Newton put the controversies to rest.
Anyways it blows my mind how recent that was, compared to how old the existence of Mankind is since creation! that is some Incredible stuff to think about!
How is the going?
You might have noticed that I haven’t been on this blog for sometime. But am back! Well may be recession might have played a role! Just kidding am doing just fine :) to quote Suze Orman the Internationally Acclaimed Personal Finance Advisor.
Anyways I have to apologize in advance coz I know I will surely be in trouble on this post, I will get some phone calls asking me to explain why on earth I can decided to write on a topic that is purely technical than on a general life experience or episode that we can all exchange ideas and contribute to, and I totally get it. To be sincere I didn’t want to, but you know I love design and at the moment not doing much of it momentarily so it’s a natural inclination for me to read a little bit just to stay current with that stuff especially on Hydrology and Hydraulics (the two most misunderstood terms even by practitioners’ themselves, but that is a whole different story).
Anyways, here we go just read as an entertainment or some novel for fun! Am sure most of you will make sense out of it, after all its English, I didn’t write it in Swahili! Some of you are going what is that? It’s a Kenyan National Language, Just like English in US!
Shifts in focus from Peak Flows Based Hydrology (PFBH) to Volume-Based Hydrology (VBH).
To start, Andrew J. Reese a vice president with AMEC Earth & Environmental Inc. quoted General George Patton famous statement “If everybody is thinking alike then somebody isn’t thinking” – you know the amazing thing that I like about this quote is that its plainly true that its counterintuitive if we all be thinking alike, this world will be boring, we will not have all the break-through that have led to industrialization age as well as advancement in technology that has immensely improved our human living conditions. Someone had to think “outside the box” to use this infamous cliché.
Anyways back to the PFBH vs. VBH. Just to give a preview of what shifts have been made in Urban Stormwater "Practitioning", Let see Sixty years ago, efficient drainage was the way to do things, using separate stormwater systems of pipes. Forty years ago, efficient drainage was causing flooding problems and switched to a detention design standard. Twenty years ago, detention ponds were failing for a number of reasons and switched to a more comprehensive master planning approach—that is, those who could afford all that modeling, understand its output, and had the wherewithal to actually construct regional systems for stormwater treatment to para phrase Mr. Reese. In the ensuing 20 years, there has been a rapid diversification of stormwater design from a simple consideration of flooding and conveyance to channel erosion, stormwater pollution, groundwater recharge, and natural approaches to stormwater design.
All these past approaches to urban stormwater hydrology focused on peak flow (and flooding) and, secondarily, on velocity. Basically Peak flow was and is still key until we shift gears, the ultimate stormwater controls structures’ sizing factor (for the most part). But as we start to focus on stormwater quality, there was a recognition that we were treating volumes of runoff because we were most often trying to reduce quantities or concentrations of (versus flow of) pollution. This often led to a sort of “Frankenstein-ian,” cobbled-together approach to stormwater design where a water-quality volume is treated, but the rest of the design was still all about peak flow.
The most recent on this subject in an attempt to shift to VBH rather than PFBH is the 2007 Energy Independence and Security Act (Section 438) deals with redevelopment or new development on federal facilities, stating they must seek to maintain predevelopment hydrology with respect to temperature, flow rate, volume, and flow duration. EPA’s CSO control policy “presumptive” approach has a volume-elimination option, which has led to, among other things, a green infrastructure emphasis. This for most stormwater practitioners is a green light towards VBH.
VBH has a comprehensive stormwater management approach that focus on 5 objectives.
1. Infiltrated Flows – the Initial rainfall depth to capture as initial abstraction or infiltrate into the ground (re-charge ground water). On the other hand though we have to be careful when doing this since the law of unintended consequences (Murphy’s first cousin) has it that all this infiltration in an urban area can be problematic in the future just be cautious!
2. Most Populated Flows – basically as the rainfall begins to intensify the flow begins to mobilize sediments and pollutants and it makes all sense if we have to achieve removal of high % pollution then we need to capture and treat this so called “first flush”.
3. Most Erosive Flows – basically this is about somewhere btwn ¾ to bank full as the rainfall intensifies. As its well know that sediment is transported when the shear force in flowing water exceeds the ability of the bank and bed materials to withstand the shear force. This shear stress moves sediments downstream, pulling on bed and banks; this is usually causes scouring effect to the river banks as well as beds.
4. Most destructive Flows. - Basically as the rainfall intensifies, the ability to infiltrate becomes problematic and overall volumes increases, the flows and velocity becomes violent and can be destructive. So here is where we start thinking to delay or manage excess volumes that may be over-capacity of our onsite detention / retention structures.
5. Biggest flows to consider – 100-yr storm for the most part is considered the biggest and here we tend to focus on safely passing the flow.
I hope I convinced you guys that VBH is more compressive that PFBH.
So anyways, to rationalize it my point is that “If everybody is thinking alike then somebody isn’t thinking” ( to go back to General George Patton). I think it makes a big different if we be forward thinking that just getting stuck in one old idea be PFBH or some old and tired Health System, and that is why i kind like the "dialogue" about Health care reforms atleast someone has a different opinion, that good enough!. We should be always open to change not scared to death by change, otherwise if Sir. Issac Newton (1643)didn’t out curiosity asked himself the question that no one else before him asked himself then all modern Physics including the Law of Gravity, by the way which hydrology is based on will not have been discovered.
Its mind blowing to Imagine that sixteen hundred and fourty three (1643) years before Him No else ever asked themselves the very question that Sir. Issac Newton asked himself that led to his "discovery" of the Laws of motion and later be known as the Father of Physics. Isn't that Incrediable? Given that other before him had somewhat tried to (including the Astronomer Johannes Kepler who discovered Laws of Planery motion 1571-1630) but with still controversies till Sir. Newton put the controversies to rest.
Anyways it blows my mind how recent that was, compared to how old the existence of Mankind is since creation! that is some Incredible stuff to think about!
Comments
In all seriousness though, I look at stormwater management as an attempt to maintain the harmony between man and nature. If you remember your design manuals it is all about replicating the existing conditions most of the time. Managing the volume is obviously one of the things to do from a long list. I think, the keyword here is "manage" which in this context should mean "regulate". One of the big part of regulating volume is to cutoff the peak flow, which for all practical purposes mean avoiding flooding at the downstream end. Not regulating the peak flow can result into downstream flooding, erosion of the banks, loss of life and property, the list goes on.
To me, controlling peak flows is one of the most effective way to control/regulate volume. The thought process here lies within the answer to one question "how do you effectively cutoff your peak flows (without bankrupting your client obviously)?"
I gotta get back to work here!! Hopefully I can finish my line of thoughts tomorrow!!
Anyways that is beside the point.The peak-flow method of stormwater management manifested in the detention basin,
does not obey a site specific predevelopment hydrology. yah it attenuates somewhat onsite peak flow rates which may provide some protection to nearby land owners, or downstream properties it does SO LITTLE in the way of
watershed protection and maintaining environmental integrity.
A volume-based approach
to stormwater management on the other hand obeys the predevelopment hydrologic cycle of the specific site /site of interest.