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USCA Formed: 10-Race Series For Pro Touring!
It isn't like a whole lot more proof was needed to show just how popular the Pro Touring craze has gotten in the world of hot rodding, but the creation of the Ultimate Street Car Association (USCA) and their 10-race 2014 series is irrefutable evidence. With sponsorship from companies like Optima Batteries, Lingenfelter Performance Engineering, and RideTech among others, this association is open to exotics, Pro Touring, and high-performance street cars of all types. The USCA schedule hits tracks all over the country and these are highline facilities like Laguna Seca, Road America, Daytona, and others. The culmination of the year will be the Optima Ultimate Street Car Invitational in November of 2014. We're stoked about this thing! Rumor has it a TV series is in the works to cover the events. Learn more at UltimateStreetCar Association.com. —Brian Lohnes
Popp Wins Goodguys Shootout
From what started out as a way to get people out of their lawn chairs and into their driver seats at their car shows, the Goodguys Rod and Custom Association autocross series has evolved into one of the most intense and talent-laden venues in all of motorsports. The season-long string of autocross events culminated in Scottsdale, Arizona, where event winners squared-off in a shootout style of eliminations. This year, it was Danny Popp in the Lingenfelter-powered 1972 Corvette that's been in his family for decades who took the win. Popp is a multi-time SCCA National autocross champion and one of the best pure drivers on an autocross course. The 1972 Corvette he drove has been in his family since his dad bought it new, and now has Lingenfelter power, JRi shocks, and Vansteel suspension. He took on a field that was chock full of other former SCCA champions and Goodguys winners from across the country. This was probably the greatest assemblage of autocross talent ever outside of SCCA national championship runoff events. Look for more coverage of the Scottsdale Autocross Shootout in next month's issue! —BangShift.com
2014 AMSOIL Engine Masters Challenge
Presented by Popular Hot Rodding
Popular Hot Rodding magazine has begun accepting competition applications for the 2014 AMSOIL Engine Masters Challenge, which will be held the week of October 6-10, 2014 on the campus of the University of Northwestern Ohio. The journey all starts with the selection process—but to be selected to compete, you have to apply. Want to know what motors will be allowed? How the competition will be scored? What other changes we're making to the rules? We bet you're curious how we're going to mix things up for 2014! One thing's for sure, it's going to get interesting if the PHR staff has its way. Up-to-date rules and the official application form may be found by logging on to EngineMasters.com. The deadline for application is Monday, February 17, 2014. We hope to see yours in the mail by then! —Johnny Hunkins
GM Teases Gen V LT1 Crate Package
OK, so you've been reading about every automotive journalist on the planet having a mechanical religious experience over the new Corvette. Everyone is in love with the suspension, seven-speed manual transmission, and interior, but the real star of the show is the direct-injected LT1 engine. Recently, Chevrolet Performance floated one of their famous "concept" ideas in front of us, and like throwing steak in front of a lion we ate it up. The engine that was shown is the 460hp/465 lb-ft version that appears in the C7 Corvette. There are less powerful versions available in trucks, but who wants those?! The engine is all aluminum, has direct fuel injection, is stupid efficient, light, and basically stands as the natural successor of the famed LS engines that have dominated swaps and hot rodding for a decade now. This engine shares the LS's compact design and will plug right into any place an LS would fit. We know of outfits already modifying these engines with superchargers and computer tuning to crank out 600-plus horsepower with little effort. We are excited to hear about this program! —Brian Lohnes


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Press Release Source: Kansas City Southern On Thursday September 23, 2010, 4:41 pm EDT
KANSAS CITY, Mo.--(BUSINESS WIRE)--Kansas City Southern (KCS) (NYSE: KSU - News) today announced the appointment of Douglas W. Vogl as vice president of audit and enterprise risk management. Mr. Vogl will report to KCS executive vice president and chief financial officer Michael W. Upchurch.
"Doug is well known in Kansas City as an audit and risk management expert," said Mr. Upchurch. "We are pleased that he will bring to KCS his expertise from auditing and performing enterprise-wide risk management assessments, SOX audits, compliance reviews, operational audits and IT audit consulting for a variety of industries."
Mr. Vogl joins KCS from PricewaterhouseCoopers (PwC), where he spent 10 years leading and developing the internal audit and consulting practice. Prior to joining PwC, Mr. Vogl worked in the information technology division of FedEx and has extensive experience in systems design, development, implementation and administration.
Mr. Vogl holds a master of business administration from Benedictine College and a bachelor of science in information technology management from Christian Brothers University. He is a certified information systems auditor and a certified information systems security professional.
Headquartered in Kansas City, Mo., KCS is a transportation holding company that has railroad investments in the U.S., Mexico and Panama. Its primary U.S. holding is The Kansas City Southern Railway Company, serving the central and south central U.S. Its international holdings include Kansas City Southern de Mexico, S.A. de C.V., serving northeastern and central Mexico and the port cities of Lázaro Cárdenas, Tampico and Veracruz, and a 50 percent interest in Panama Canal Railway Company, providing ocean-to-ocean freight and passenger service along the Panama Canal. KCS' North American rail holdings and strategic alliances are primary components of a NAFTA Railway system, linking the commercial and industrial centers of the U.S., Mexico and Canada.

subset: commoncrawl


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You're Not Alone
Mentors help with everything from emotional support to classroom strategies.
By Amy Buffenbarger
We're not going to lie. Your first year teaching is going to be a challenge.
The important thing to remember is that you're not alone. Veteran teachers—many participate in mentoring programs created by your state or local Association—can help.
Consider New Jersey's Support on Site (SOS) program. About a decade ago, several teachers in the state's Gloucester Township noticed new teachers leaving the profession. Angel McDermott—president of the Gloucester Township Education Association—was one of the veteran teachers who wanted to reverse the trend.
McDermott and several colleagues started monthly SOS meetings so new teachers could hang out and talk with their more experienced counterparts about obstacles they faced in the classroom. The informal and confidential meetings, which are led by an SOS facilitator, continue today.
"The idea was that this program would be a safe haven for new teachers to be able to come and pick up some vital skills on things like how to run a classroom, how to engage with parents—the do's and don'ts they don't teach you in college," says McDermott.
With the support of the New Jersey Education Association, SOS has rolled out statewide.
"It's been very positive in building bridges between younger teachers and veteran teachers—so it's not an 'us versus them' thing," says McDermott. "It makes for a stronger community of teachers in the building and a stronger Association."
"It helped me acclimate to a new school, a different position, and find out various things—like how to run a parent teacher conference and how to fill out report cards," says Guillama.
And SOS isn't just a one-way exchange of advice from veterans to new teachers. Earlier this year an entire SOS meeting was dedicated to Pinterest, with younger members explaining how teachers can use the site to find ideas for their classrooms.
"SOS has been a really good way to meet people and socialize," explains Guillama. "Because we have a mix of new and veteran teachers, we cover topics interesting to everyone."
In Hampton, Va., new teachers get double support. Regardless of their level of experience, new hires are paired with a mentor in the same school building. New teachers also receive a retired-teacher mentor.
In 2002 the Hampton Education Association, the Virginia Education Association (VEA), and VEA-Retired used $8,000 from the NEA-Retired grant program to create a mentoring program that pairs new and retired teachers. The program was so successful that when funding for the grant ran out, Hampton City Schools picked up the program to keep it running. Local universities joined, too.
Retired teachers apply through the program to become mentors. Once they've been selected, mentors receive training on coaching techniques that will help them ask the types of questions that will allow new teachers to take ownership of their experiences.
"It's more collaborative that way," explains Su Lively, a 30-year preschool and kindergarten teacher—now working as a teacher specialist—who coordinates and trains mentors for Hampton City Schools. "You can't just tell a new teacher what to do. The key is for the mentors to be a resource and know what questions to ask the teacher to help them process what to do themselves."
For Annette Crothers, the emotional support from her retired mentor helped get her through the first year of teaching with confidence.
"My first year would have been totally different if I hadn't had my retired mentor," says Crothers, now in her third year teaching language arts. "Being a first-year teacher, you're not sure if what you are going through is the normal thing. My mentor let me know I wasn't alone. I knew she was invested in helping my classroom and helping me be the best teacher I can be."
Often, retired mentors can provide more time and opportunities for confidential conversations than teachers who are balancing their own classes and workloads in the same school. For some, the mentor/mentee relationship develops into a friendship after the first year.
"If I ever need help my mentor still comes to visit," says Crothers.
Created by the Washington Education Association, and implemented by The Virginia Education Association in 2006, Sparks helps new members gain a better understanding of their Association while learning skills and making connections.
Every February, approximately 100 new teachers and education support professionals (ESPs) from across the state gather at a ski resort in Virginia at no cost to the member. During the participant-led weekend, new teachers talk about the joys and trials of being an educator, explained Tami Sober, assistant director of the Office of Teaching and Learning for VEA.
During the event, trained facilitators model best practices and lead conversations about issues like classroom management. Attendees also participate in team-building activities and learn what it means to work collectively with the Association. Sober says that approximately 50 percent of Sparks' attendees assume leadership roles with the Association.
Pioch had such a great experience during the Sparks weekend, he decided to "pay it forward" and become a facilitator. "As a facilitator, my number one objective is to listen. I try to recreate my experience each time I facilitate," says Pioch.
For Samantha Killion, meeting other members from different parts of Virginia and interacting with VEA staff who could "help me develop my career" was a big benefit of the Sparks weekend.
"At worst you end up with a free weekend at a ski resort," says Killion, who is also a facilitator now. "At best you start to figure out your career and who you're going to be as a teacher."
And at the very best, it's safe to say that mentoring helps teachers develop skills much quicker than they would on their own. If your school doesn't have a formal program, reach out to your local Association through the building representative and ask for help.


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Education Program
Welcome to Lunarpages FREE Web Hosting Program for Schools.
Educational websites are an extraordinary tool for teachers, students and parents alike. Lunarpages provides free web hosting to U.S. public schools, grades K-12. We are proud to know that by donating our web hosting services to public schools across the country, we are, in fact, making a huge impact on our educational system at large.
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For more information, or to sign-up for Lunarpages Education Program, please fill out the form below or contact us at firstname.lastname@example.com, or 1-877-586-2772.
Need Lunarpages banners for your education and donated hosted website? Find them here.
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Applications/nominations invited for C&RL editor
For Immediate Release
Tue, 06/24/2014
David Free
Marketing and Communications Specialist
Association of College and Research Libraries (ACRL)
CHICAGO — Applications and nominations are invited for the position of editor of College & Research Libraries (C&RL), the scholarly research journal of the Association of College and Research Libraries (ACRL). The association seeks an innovative, experienced candidate to lead its top-tier, open access journal with an eye to the future of scholarly publishing. The editor is appointed for a three-year term, which may be renewed for an additional three years. Applicants must be a member of ALA and ACRL at the time of appointment.
Qualifications include:
- Professional experience in academic libraries;
- Broad knowledge of current issues facing academic and research libraries;
- Record of scholarly publishing;
- Editing experience, preferably in the scholarly publishing environment;
- Knowledge of, and experience with, current trends and innovations in scholarly communication, including open access and digital publishing;
- Knowledge of current trends in reader engagement, including social media integration; and
- Organizational and communication skills, including the ability to meet, and hold others to, publication deadlines.
Some funding for editorial assistance and travel to relevant conferences is available, and there is a small honorarium for the editor.
Appointment will be made by the ACRL Board of Directors at, or prior to, the 2015 ALA Annual Conference upon the recommendation of the search committee and the ACRL Publications Coordinating Committee. The incoming editor will serve as editor-designate for one year before assuming full responsibility for C&RL in July 2016.
Nominations or resumes and letters of application, including the names of three references, should be sent to:
C&RL Search Committee
c/o Dawn Mueller
50 East Huron Street
Chicago, IL 60611
The deadline for receipt of applications is October 31, 2014. Finalists will be interviewed at the 2015 ALA Midwinter Meeting in Chicago or by phone shortly after Midwinter.
The Association of College & Research Libraries (ACRL) is the higher education association for librarians. Representing more than 11,500 academic and research librarians and interested individuals, ACRL (a division of the American Library Association) is the only individual membership organization in North America that develops programs, products and services to help academic and research librarians learn, innovate and lead within the academic community. Founded in 1940, ACRL is committed to advancing learning and transforming scholarship. ACRL is on the Web at www.acrl.org/, Facebook at www.facebook.com/ala.acrl and Twitter at @ala_acrl.


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Excerpt from Bob's interview with Gordon Brockhouse of Audio Ideas Guide:
Link: http://www.audio-ideas.com/interview/carver.html
BC: Having left Carver I wanted to build a product that people would really notice. A very small subwoofer would certainly attract attention…provided it had performance. The smallest box I could fit a driver with a 10-inch basket into was 11 by 11 by 11inches.
GB: The power specification for the True Subwoofer - 2,700 watts - has been controversial.
BC: No one believes it, because the amp's the size of a candy bar, albeit a big $2.25 Hershey bar. When Don Keele, a world-respected subwoofer scientist and reviewer, measured it, he measured 2,500 watts continuous for at least two minutes. And it's capable of twice as much peak output - maybe 5,000 watts.
GB: Is it just raw power that enables you to get so much bass from so small a box?
BC: The True Subwoofer is a small box with a small driver that produces the same output and bass extension as a large box with a large driver. It has not been possible until now to build a small subwoofer with this kind of output. Conventional drivers are not very efficient at converting input power into motion. They operate close to "stall mode" where a lot of power is turned to heat. To get lots of output from a small box, we have to increase input power by a factor of 10 or more. Two hundred watts becomes 2,000 watts, and that burns out the voice coil. What was necessary was to make a driver that would remain highly efficient even in a small box. This requires a big magnet and lots of motion, which pulls the driver out of stall. When it's out of stall, it's efficient and there's far less heat.
This flies in the face of conventional driver design, because that type of driver generates vast amounts of back emf [back electromotive force, which results when the motion of the voice coil in the magnet gap generates a voltage]. The back emf prevents current from flowing through the voice coil, so there isn't any output. To overcome the back emf, you need a special amplifier that can swing 100 volts, rather than 20 or 30 volts. When you compute the input power - 100 volts squared divided by four ohms, the resistance of the speaker - that's over 2,000 watts. That's what the amplifier would deliver if the load were purely resistive. But it's not. It's a loudspeaker load with high back emf. The real power delivered to the voice coil is only a few hundred watts.
GB: Is that the explanation of the controversial power specification of the True Subwoofer? That its amplifier delivers a few hundred watts into the resistive component of the load, but that it has to be capable of delivering far more power in order to deal with the reactive component of the load.
BC: You can think of it in those terms. That's called "imaginary power."
GB: I lose the ability to think when people start talking complex arithmetic and imaginary numbers.
BC: It's hard. I'd forget about it at this point.
GB: What was the basic insight that led to the True Subwoofer?
BC: Necessity is the mother of invention. This woofer began two-and-a-half years ago with an eviction notice from my wife Diana. "Get this stuff out of the room," she said. "If you want to have a big woofer in the room, it has to be invisible." I began thinking of ways to do this. I'd think about when I was driving around, when I'd go to an opera, when I was going to sleep at night. Gradually, it occurred to me that one of the fundamental defining equations for efficiency, (Bl)2/re [where B is magnetic strength, l is voice-coil excursion, and re is voice-coil resistance], is true over all frequencies, not just for the midband as the equation is classically interpreted. It turns out I was right. That meant I could increase output and bass extension by using a big magnet and long-excursion driver.
GB: It sounds like a very unusual driver design.
BC: Oh yes. It requires careful attention to the suspension, surround and the magnetic geometry to keep it linear. They can't collapse under the box pressures, which are around 150 pounds. So the rubber-rolled surround has to be sufficiently rigid so that it doesn't cave in and act like a passive radiator in reverse.
GB: How do you obtain acceptable transient response with materials sufficiently massive to withstand these pressures and produce these excursions?
BC: Transient response is the mirror of frequency response. If you have good amplitude response, you have good transient response. If you have good transient response, you have good frequency response. The trick is to get the amplitude response correct, which is challenging enough. It requires good motor structure, good surround design, a good amplifier, the proper equalisation and so on.
GB: What about sensitivity?
BC: Sensitivity is so low it's preposterous. It's not so much the mass, although that does drive down sensitivity. The main thing is the back emf associated with the large magnet. The sensitivity is somewhere in the 60s or 70s [dB @ 1 watt @ 1 metre]. But it doesn't matter because I've got this super amplifier to drive it.
GB: Isn't distortion high with such a small box and driver?
BC: At full output, distortion is less than 10 per cent from 18 Hz upward. Most subwoofer manufacturers don't specify distortion, because it's very high: 10, 20 per cent or more. Even the Velodyne, which has a high-gain servo system, has one per cent distortion at low levels; but at full output, distortion is close to 10 per cent.
GB: How tolerant is human hearing of distortion at very low frequencies?
BC: Incredibly tolerant. It's all but impossible to hear distortion at very low frequencies.
GB: Some speaker manufacturers maintain that distortion is important at those frequencies.
BC: Believing in low distortion is like believing in motherhood and apple pie. Low distortion is a good thing, and every manufacturer strives for ever-lower distortion. But it's well-known how much distortion we can hear, and at what levels and under what circumstances we can hear it. If we apply those rules artfully, we can design products with vastly improved performance.
Take DVD as an example. DVD contains immense amounts of distortion as a result of the compression algorithms used for audio and video. A lot of information is thrown away. The components in the signal that are tossed out represent tremendously high distortion. But we don't notice it because the designers know what's important and what's not.
Philosophically and conceptually, any audio product can be approached that way. It's impossible to hear 20 per cent distortion if the thing's operating at 9 Hz, because the first overtone is below the threshold of audibility unless it's so loud that it's hurting your ears � 130 dB or more.
GB: What about when you move higher in frequency?
BC: The thresholds change, but the rule still applies.
GB: In addition to the active driver, the True Subwoofer has a mass-driven unit that moves out when the active woofer moves out, and moves in when the active unit moves in. You'd expect the outward movement of the active unit to pull the mass-driven cone in, and vice-versa. How is the mass-driven woofer made to operate in phase with the active woofer?
BC: The force that moves the driven woofer is the electricity going through the voice coil. The force that moves the other woofer is the reaction force. To understand how this works, imagine standing on a chair and holding a Slinky in your hands. Pretend there's a little weight on the other end of the Slinky. Your hand represents the voice-coil-driven woofer. The springs in the Slinky represent the spring of the air in the box, and the mass on the bottom represents the mass glued onto the other woofer. If you start moving that Slinky up and down with your hand, when your hand goes down, the bottom end of the Slinky comes up, and when your hand comes up, the bottom end of the Slinky goes down. It's just the opposite of what you'd expect.
GB: That's when the rate of movement is above the resonant frequency of the system.
BC: Correct.
GB: So you get this spring effect in the subwoofer whenever the input frequency is above the resonant frequency of the subwoofer, which, given the driver design, must be very low.
BC: It's 18 Hz.
GB: Is the new 13-inch version of the True Subwoofer just a bigger cousin, with a little more output and lower extension?
BC: The Signature Subwoofer is the same system, but slightly larger. It has 6 dB more output, 116 dB as opposed to 110 dB, and it's tuned to 16 Hz rather than 18 Hz. It uses the same amplifier, but larger drivers � equivalent to a 10 1/2-inch driver rather than eight inches.
Gordon Brockhouse interview with Bob: Sunfire Subs excerpt
Interesting facts/opinions about the man himself.
Post Reply
3 posts • Page 1 of 1
- TNRabbit
- R.I.P. Friend
- Posts: 13360
- Joined: Sun Jan 14, 2007 11:53 am
- Location: TN Native Languishing in VA
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Gordon Brockhouse interview with Bob: Sunfire Subs excerpt
From FrankieD's lips to your ears: Sunfire - a quiet box of endless power.
Sunfire TG-IV/400~7 Amp
Carver SD/A-360 CDP
Benchmark DAC-1
Sony SACD/DVD-A
Active bi-amp: Ashly XR-1001 & 2 Rane PEQ-15s
Main: HotRodded AL-IIIs
Sub: Klipsch RT-12d
Center: Sunfire CRS-3c
Surround: Sunfire CRS-3 (x 2)
RIP WIlliam B. Dibble, 1948-2012. I'll miss you my friend.
From FrankieD's lips to your ears: Sunfire - a quiet box of endless power.
Sunfire TG-IV/400~7 Amp
Carver SD/A-360 CDP
Benchmark DAC-1
Sony SACD/DVD-A
Active bi-amp: Ashly XR-1001 & 2 Rane PEQ-15s
Main: HotRodded AL-IIIs
Sub: Klipsch RT-12d
Center: Sunfire CRS-3c
Surround: Sunfire CRS-3 (x 2)
OconeeOrange wrote:"Gary likes to play it 'loud' as do I. His system begs you turn it up until you die"
RIP WIlliam B. Dibble, 1948-2012. I'll miss you my friend.
- thuffman03
- !! CarverFest Evictee !!
- Posts: 2701
- Joined: Fri Sep 19, 2008 10:07 am
- Location: Pittsburgh, PA
Re: Gordon Brockhouse interview with Bob: Sunfire Subs exce
Very cool read! Thanks TNRabbit!
Some cool Carver stuff!
Re: Gordon Brockhouse interview with Bob: Sunfire Subs exce
Yes thanks, very interesting read!
Post Reply
3 posts • Page 1 of 1


text:
Exploring Mars from the Air
Because the Martian atmosphere is so thin, taking off from the ground would require very big wings or a very fast take-off. One solution to this problem is to have the airplane drop off an entry vehicle as it is coming into the Martian sky. As the plane drops off, the wings would unfold and it would start flying, powered either by batteries or by gliding through the air. A likely place to fly airplanes would be in valleys or other interesting places where there is a lot to see over great distances.
Although this flight would be relatively short (less than an hour), and shorter than a balloon flight, an airplane is more controllable and can be directed to closely approach areas of scientific interest. To receive even more data from an airplane, engineers are also engaged in further research that will give them insight into how to make a Mars airplane stay aloft for longer periods of time.


text:
You can search our catalog to find books, music, or movies. The catalog search box is at the top of this page and every page on our website.
If you're interested in downloading eBooks, audiobooks, or digital magazines, all you need is your library card number and your pin. You can also check out our books and reading resources for links to best seller lists and other helpful websites.


text:
WWE Hall of Famer Jim Ross is back with a new blog on jrsbarbq.com. Here are some highlights:
– Just received an advance copy of the Legends of Mid South DVD, three disc set for my review. This long awaited collection will be released September 10 in the USA and about a week later in the UK as I understand it. I had the chapters and the full match lineup in a blog here on the site a couple of weeks ago but apparently my blogs are not widely read as the IWC is just now printing the list and crediting others for providing it. Drat…thought I had a scoop.
– Less than a week away from the July 11 grand opening of the new, WWE Performance Center in Winter Park, Florida. Invitations have been extended to many and I'm expecting this to be a huge event/turnout celebrating a milestone day in WWE. If we are able to consistently bring in charismatic, world class athletes into this facility the future of WWE will be even brighter.
– My Twitter, @JRsBBQ, timeline is being hammered with the latest Sting rumors of him coming to WWE at some point in the future. Are these rumors of any significant difference than the basic, same ones that we've been hearing since WCW closed their doors or every time Sting's contract nears it's end? As best that I know, Sting is very happy where he is currently working and has no plans to launch a WWE in ring career at the age of 54. I've known Sting since day one and have immense respect for the man and do feel that he will be a WWE HOFer some day. There's some cool stuff on the Mid South DVD with Sting and his tag team partner Rock aka Ultimate Warrior in their Blade Runner incarnation.
I cannot predict the future but these daily, Sting-to-WWE rumors are merely internet dribble and are unfounded although they always seem to make for interesting fan chatter. Obviously, something as simple as Sting appearing in a WWE promo last week in the build to the WWE vs. World Title match featuring Cena vs. Del Rio likely fueled this fire, too.
WWE Talking with Another Big Name, Backstage News on Lesnar's Future, More


text:
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Program update AVG 2016 INTERNET SECURITY 7687 SMALL UPDATE 9
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Program update AVG E-mail Server 2012.2126 Service Pack 1
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- EMS Exchange: Phishing flag is ignored for messages from sender on white list.
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Special Collections houses approximately 15,000 items. Some of these items are rare or unique and most require special handling and preservation.
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Fatima Jane Stanley Richards (1825-1912; first row, in chair) was my 3rd great-grandaunt.
Hello there,
I posted on your wall awile ago about the five generation photo. I was searching for a death record for fatima, and was hoping that you had one. If so, I would like to have a copy and I will send you the money to send it. Thank you for your time.
Shaun K. Young
I do so love the double five generation photograph of fatima jane stanley richards and the family. My great grandmother is being held in her mother's arms at the age of 2 yrs.
Myself and another family member have sat down and have been able to identify half of the people in the photo.
Thank you for sharing the photo to the world.
Shaun K. Young
P.s. I am still looking for mor info on the family, hoping you might have what I need. Thank you…
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text:
IN THE end, Harris v. Quinn did not turn out to pose the deadly menace to U.S. labor that pre-decision hyperbole had warned of. Not a single Supreme Court justice accepted anti-union litigants' invitation to overturn precedents under which public-sector unions may charge non-members a mandatory fee — a power that prevents "free riders" and helps assure organized labor's financial viability at a time when private-sector unionism is in decline. As such, the court's decision was prudent and a victory for stare decisis, the wise principle that the justices leave settled doctrine alone except in extraordinary circumstances. State workers may still organize and bargain collectively and insist on the financial support of members who benefit from that service even if they disagree politically with the union.
What the Supreme Court did do, in a 5 to 4 decision, was curb the ability of unions such as the Service Employees International Union to sign up Medicaid-funded home health-care workers as members, bargain on their behalf with state governments and charge them a mandatory fee — even where the home health care workers aren't clearly state employees. That was the situation in Illinois, where, since 2003, SEIU has been the exclusive bargaining representative of some 27,000 caregivers across the state — many of them family members of the aged or disabled, and all of them directly hired by their customers, subject only to very broad state regulation. Because they drew on a state funding source, Medicaid, Illinois law declared them public employees — though only for purposes of labor law, not for less convenient purposes such as legal liability for any personal injuries they might cause.
In striking down Illinois's system, Justice Samuel A. Alito Jr. wrote for the majority that, given this murky status, "labor peace" and other claimed public benefits of making the caregivers pay union fees were not enough to outweigh their First Amendment right not to fund an organization with which they might disagree. The line separating any union's political activities from collective bargaining can be blurry when its counterpart is the inherently political state itself. The line may be blurrier still when the union is a highly partisan one such as SEIU, which has been trying, with some success, to boost dues-paying membership, and hence its political war chest, by lobbying for laws in blue states such as Illinois.
Maryland enacted a statute similar to Illinois's in 2011, though the union in question is not SEIU but the American Federation of State County and Municipal Employees. Under Mr. Alito's ruling, Maryland's law would appear to be vulnerable to constitutional challenge since it specifically says that it "may not be construed to make independent home care providers employees of the state."
Perhaps courts should usually assume that states know best about devising collective bargaining rules for their own employees, as Justice Elena Kagan argued in dissent. Whether that deference should extend further, to non-transparent state decisions that define people as employees for selected purposes but not others, is a harder question, which the court in this case plausibly answered in the negative.


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Journal of the South African Institution of Civil Engineering
versão On-line ISSN 2309-8775
versão impressa ISSN 1021-2019
J. S. Afr. Inst. Civ. Eng. vol.54 no.2 Midrand Jan. 2012
Catchment parameter analysis in flood hydrology using GIS applications
O J Gericke; J A du Plessis
The use of Geographical Information Systems (GIS) has permeated almost every field in the engineering, natural and social sciences, offering accurate, efficient, reproducible methods for collecting, viewing and analysing spatial data. GIS do not inherently have all the hydrological simulation capabilities that complex hydrological models do, but are used to determine many of the catchment parameters that hydrological models or design flood estimation methods require. The purpose of this study was to perform catchment parameter analysis using GIS applications available in the ArcGISTM environment. The paper will focus on the deployment of special GIS spatial modelling tools versus conventional manual methods used in conjunction with standard GIS tools to estimate typical catchment parameters, e.g. area, average catchment and watercourse slopes, main watercourse lengths and the catchment centroid. The manual catchment parameter estimation methods with GIS-based input parameters demonstrated an acceptable degree of association with the special GIS spatial modelling tools, but proved to be sensitive to biased user-input at different scale resolutions. GIS applications in an ArcGISTM environment for the purpose of catchment parameter analyses are recommended to be used as the standard procedure in any proposed hydrological assessment.
Key words: catchment parameters, GIS, DEM, average slope, flood hydrology e.g. area, average catchment and watercourse slopes, main watercourse lengths and the catchment centroid.
The use of Geographical Information Systems (GIS) has permeated almost every field in the engineering, natural and social sciences, offering accurate, efficient, reproducible methods for collecting, viewing and analysing spatial data. These spatial data sets represent the key components in the hydro-logical response of catchments to storm rainfall and the resulting runoff. GIS do not inherently have the hydrological simulation capabilities that complex hydrological models do, but are used to determine many of the catchment parameters that hydro-logical models or design flood estimation methods require.
In hydrological catchment parameter analyses, a Digital Elevation Model (DEM) and spatial data sets represent the two fundamental data sets initially required. The DEM contains raster information of the catchment and surrounding areas, while the spatial data sets contain the spatial information which originates from other sources than the DEM. The DEM is used to do a complete catchment parameter analysis, including the determination of flow directions, catchment areas, land surface and river channel characteristics. The spatial data sets contain layers of combined spatial information used to analyse the spatial distribution and associated attributes of geology, soil, land use and vegetation.
In addition to catchment parameter analysis, GIS also provide a powerful data management framework with a consistent, intuitive platform for organising and analysing relationships amongst the spatial variables and information associated with those variables encountered in the field of flood hydrology. Various GIS software packages exist. This paper will, however, only refer to the Environmental Systems Research Institute (ESRI) GIS software in the form of ArcGISTM 9.3.
The purpose of the study is discussed and explained in the next section, followed by an overview of the study area's spatial distribution and characteristics. In the section thereafter, the methods used in South Africa to estimate catchment parameters are reviewed in detail. The methodologies involved in assessing the paper's purpose and objectives are then expanded on in detail, followed by the results, discussion and conclusions.
The purpose of this study was to perform catchment parameter analysis using GIS applications available in the ArcGISTM environment. The focus was on the deployment of special GIS spatial modelling tools versus conventional manual methods used in conjunction with standard GIS tools to estimate typical catchment parameters, It was hypothesised that the accuracy of conventional manual procedures used in flood hydrology to establish typical catchment parameters could be improved by using automated GIS input processing functionalities, since manual inputs are regarded as insufficiently accurate and outdated. It was further hypothesised that the spatial distribution of slope classes, used as primary input data to the deterministic flood estimation methods, are not sufficiently representative of the specific conditions under evaluation. Many practitioners in the field of flood hydrology typically ignore the importance thereof and follow a "thumb-suck" approach. In addition, hydrologists and engineers are frequently doubtful when deciding on, or determining, the position of the catchment centroid.
The study area covers 34 795 km2 between 28°25' and 30°17' South and 23°49' and 27°00' East, and comprises the C5 secondary drainage region. The tertiary drainage regions of concern are C51 (Riet River Catchment (RRC)) and C52 (Modder River Catchment (MRC)), covering an area of 17 435 km2 and 17 360 km2 respectively. The MRC and RRC consist of eleven and twelve quaternary catchments respectively (Midgley et al 1994). The topography is gentle (average quaternary catchment slopes between 2,4% and 5,5%), while the mean altitude above sea level varies between 997 m and 2 122 m (NASA 2002).
Twelve catchments with contributing catchment areas consisting of either single or multiple C51 or C52 quaternary catchments were evaluated individually in the study area. A Department of Water Affairs (DWA) flow- gauging station is situated at the outlet of each of these catchments. The flow-gauging station numbers were therefore used as the catchment descriptor for easy reference in all the Tables and Figures included in this paper. The general information applicable to these catchments is listed in Table 1, while the location thereof within the study area and in relation to the primary drainage regions of South Africa is shown in Figure 1.
To provide the background for further discussion, the manual and automated methods used in design flood estimation to establish catchment parameters, will now be discussed briefly.
Catchment area
The standard maps recommended to manually determine the catchment areas for use in flood hydrology are either the 1:50 000 scale topographical maps and/or 1:10 000 scale orthophotos. The latter are normally used if the catchment area under consideration is less than 10 km2. The manual procedure to determine the catchment area entails that the demarcated catchment boundary on the map is copied onto graph paper, after which the number of squares within the catchment are counted by including squares more than halfway into the catchment. A conversion factor is then used to convert the number of squares to the catchment area in km2 (Alexander 2001). Planimeters are also still in use to measure the manually demarcated catchment areas.
Alternatively, the aforementioned standard maps in an electronic format can be imported to a suitable Computer-Aided Design (CAD) environment as a picture file, after which standard CAD functions are used for the demarcation and area calculation respectively. The use of Google Maps as alternative is also worthwhile to consider.
In an ArcGISTM 9.3 environment, the Watershed tool contained in the Hydrology toolset of the Spatial Analyst Tools toolbox (Figure 2) can be used to identify catchment areas for specified pour points representative of the catchment outlet. However, a hydrologically correct and depressionless DEM must be prepared for these calculations, using most of the tools contained in the Hydrology toolset.
Average catchment slope
Slopes, whether gentle or steep, influence the catchment response time and hence the duration of critical rainfall intensity and resulting peak discharges and volumes (Alexander 2001). The average catchment slope (S) can be determined by using any one of the Grid, Empirical or Neighbourhood methods in conjunction with standard tools available in the ArcGISTM 9.3 environment.
Grid method
A grid of at least 50 squares must be superimposed over the catchment area. At each grid intersection point, the horizontal (shortest) distance between the contour intervals which straddle the grid point along a line that passes through the grid point, is measured. The average catchment slope is consequently defined as the average slope perpendicular to the nearest contour line at each grid point. This is presented diagram-matically in Figure 3 and expressed by Equation 1 (Alexander 2001).
S1 = average catchment slope (m/m)
AH = contour interval (m)
Li = horizontal distance between consecutive contours (m), and
N = number of grid points.
Empirical method
According to Schulze et al (1992), the average catchment slope can be determined by making use of the following empirical relationship (Equation 2):
S2 = average catchment slope (m/m)
A = catchment area (km2)
AH = contour interval (m), and
M = total length of all contour lines within the catchment (m).
Equation 2 is not widely used, especially due to the tedious task to determine the M values manually. However, the use of Equation 2 in its more rudimentary form (derived from first principles), in conjunction with standard functions in ArcGISTM, will be highlighted further in the Methodology.
Neighbourhood method
This method is also known as the Average Maximum Technique (Equation 3) and is included as the standard slope algorithm in the ArcGISTM environment to generate slope rasters from raw DEM and/or point elevation GIS data sets to enable the determination of average catchment slopes and steepness frequency distributions. The slope raster generation is based on a cell matrix approach which represents the maximum change in elevation over the distance between the cell and its eight neighbouring cells. Typically, in a 3 x 3 search window (grid network with nine cells, C1 to C9), eight grid points from the surrounding cells are used to calculate the average slope of the central cell (Cs) using unequal weighting coefficients, which are proportional to the reciprocal of the square of the distance from the kernel centre (Jones 1998; ESRI 2006b).
S3 = average catchment slope (m/m) Az
= rate of change of the slope surface in a horizontal direction from centre cell
= rate of change of the slope surface in a vertical direction from centre cell][
C1-4/6-9 = surrounding cells
Cs = centre cell
N = number of grid points or cells
Xc = horizontal cell size, and
yc = vertical cell size.
Length and average slope of main watercourses
The main watercourse is a defined flow path along which water will travel the longest time to reach the catchment outlet from a point on or near the catchment boundary. This distance can be measured manually on orthophotos or topographical maps by using dividers set at a predefined incremental distance which is a function of the map scale (Alexander 2001). The average main watercourse slope can be determined manually by using the following methods (Alexander 2001; Van der Spuy & Rademeyer 2010):
Equal-area method
An average slope line is drawn or positioned in relation to the longitudinal profile of the main watercourse in such a way that the area above (A1) this line equals the area below (A2) the line. This relationship is expressed by Equation 4 and illustrated in Figure 4.
SCHI = average main watercourse slope (m/m)
HB = height at catchment outlet (m)
Hi = specific contour interval height (m)
L = length of main watercourse (m), and
Li = distance between two consecutive contours (m).
10-85 method
This method was developed by the United States Geological Survey (USGS) and is the most widely used in South Africa (SANRAL 2006). This relationship is expressed by Equation 5 and illustrated in Figure 5.
SCH2 = average main watercourse slope (m/m)
L = length of main watercourse (km)
H0,085L = height (m) of main watercourse at length 0,85L, and
H010L = height (m) of main watercourse at length 0,10L.
Taylor-Schwarz method
This method is preferred by the Department of Water Affairs (DWA) and the Natural Environment Research Council (NERC 1975). The latter also proposed the use thereof in the United Kingdom Flood Studies Report (UK FSR 1975) (Van der Spuy & Rademeyer 2010). The main watercourse profile is subdivided into sub-reaches of which the velocities are related to the square root of the slope. The index is equivalent to the slope of a uniform channel with the same length as the longest watercourse and an equal travel time. This relationship is expressed by Equation 6 and illustrated in Figure 6.
SCh3 = average main watercourse slope (m/m)
L = length of main watercourse (m)
Li = distance between two consecutive contours (m), and
Si = slope between two consecutive contours (m/m).
In the ArcGISTM environment, both fully and semi-automated methods are available to estimate the main watercourse length. The Longest Flow Path tool which forms part of the ArcHydro toolbox automatically determines the longest watercourse. However, a hydrologically correct and depressionless DEM based on extensive input rasters with increased computing time is required. The use of semi-automated methods in conjunction with Equations 4 to 6 will be expanded on in detail in the Methodology.
Distance to catchment centroid
According to Alexander (2001), an eyeball estimate of the location of the catchment centroid is adequate. In practice, the distance to the centroid can be determined manually by using a cut-out of the catchment area to hang freely from a pin inserted close to a border of the catchment area. A string with a weight attached to the bottom, attached to the pin and hanging vertically under gravity from the pin, provides a guideline on the paper cut-out of the catchment. With the guideline drawn on the catchment, the pin is then moved to another position (approximately rotated 90° from the first position) close to the boundary of the catchment. The intersection of the two guidelines on the catchment provides the approximate position of the centroid.
In the ArcGISTM environment, the location of the catchment centroid can be automatically determined by making use of the Mean Center tool available in the Measuring Geographic Distributions toolset of the Spatial Statistics Tools toolbox, which will be expanded on in more detail in the Methodology.
To evaluate the deployment of special GIS spatial modelling tools versus conventional manual methods used in conjunction with standard GIS tools to estimate typical catchment parameters, the following procedures were followed:
Projections and catchment geometry calculations
All the relevant GIS and catchment related data were obtained from the DWA (Directorate: Spatial and Land Information Management), which is responsible for the acquisition, processing and digitising of the data. These data sets are normally presented as geographical coordinate systems; in other words, the position of a geographical location on the earth's surface is described by using spherical measures of latitude and longitude (in degrees) from the centre of the earth to a point on the earth's surface.
These geographical input data sets need to be transformed to a projected coordinate system, which portrays the curved surface of the earth on a flat surface, during which the distance, area, shape and direction, or a combination thereof, might be distorted (ESRI 2006a).
The Africa Albers Equal-Area projected coordinate system, with modification, was used during this study. This approach is best suited for land masses extending in an east-to-west orientation (as in the case of the study area), rather than those lying north-to-south. This conic projection uses two standard parallels to reduce some of the distortion of a projection with one standard parallel. Although neither shape nor linear scale is truly correct, the distortion of these properties is minimised in the region between the standard parallels. All areas are proportional to the same areas on the earth, while distances are most accurate in the middle latitudes (ESRI 2006a).
The standard parallels were established by using the one-sixth rule by determining the range in latitude (degrees) north to south, divided by six. The first standard parallel is positioned at one-sixth the range above the southern boundary and the second standard parallel minus one-sixth the range below the northern boundary (ESRI 2006a). These modifications are listed in Table 2.
The specific GIS data features classes (lines, points and polygons) applicable to the study area, and individual sub-catchments were extracted and created from the original GIS data sets by using the Clip tool available from the Extract toolset contained in the Analysis Tools toolbox. The Clip tool cuts out a piece of one feature class using one or more of the features in another feature class as a cookie cutter. Either the tertiary or quaternary drainage region polygons were used as clip feature classes, since a clip feature class has to be a polygon. The data extraction was followed by data projection and transformation, editing of attribute tables and recalculation of catchment geometry (areas, perimeters and distances).
Digital Elevation Model
The Shuttle Radar Topography Mission (SRTM) elevation data for southern Africa at 90 metre resolution (NASA 2002) was extracted, projected and transformed for the study area and used as the DEM. An alternative DEM was also generated by making use of point elevation and/or contour data as the input features. The Interpolation toolset contained in the Spatial Analyst Tools toolbox was used to generate rasters for the DEM interpolation process. The input features (contours or point elevations) were selected, the Output Surface Raster was specified and Tolerance 1 was set to a value of 10, which is equal to half the contour interval, or set to zero if point elevations are predominately used. The Output Cell Size, which specifies the output raster cell size, was then selected. A smaller cell size increases the amount of cells in the raster matrix with both an increased accuracy and computing time. A trade-off between time and accuracy was used in selecting the output cell size.
Average catchment slope
The average catchment slope of the study area, as well as of individual catchments, was determined by using the following manual methods with GIS-based input parameters:
Grid method
The Create Vector Grid tool available in the Sampling toolset of the Hawth's Analysis Tools toolbox was used to superimpose a grid over the catchment areas. Refer to Figure 7 for the Create Vector Grid data input screen. In Figure 7, the Extent selection was in accordance with the extent of the catchment boundary under consideration, while polygon features were selected as the required Output, since this option enables geometry (area) calculations. Shapefiles containing the polylines as feature type were created in ArcGISTM, via the Sketch tool accessible from the Edit toolbar, to represent the horizontal distances measured at each grid intersection point between two consecutive contours (e.g. Figure 8). The attribute table of each developed shapefile was edited and the length of each polyline was determined by making use of the Calculate Geometry function. These attribute tables were then exported to Microsoft Excel for further computations.
It is important to note that the Hawth's Analysis Tools Version 3.27 (Beyer 2004) is not a standard toolbox available in ArcGISTM 9.3, but it can be downloaded from either www.ESRI. com or www.spatialecology.com/htools. However, this toolbox is only compatible with ArcGISTM 9.3 or earlier versions, since the ArcGISTM programming interface (ArcObjects) changed with the update to ArcGISTM10. In this new version of ArcGISTM the Hawth's Analysis Tools was replaced with a toolbox known as the Geospatial Modelling Environment (GME). The GME incorporates most of the functionality of its predecessor, but has a greater range of analysis and modelling tools, supports batch processing, offers new graphing functionality, automatically records work-flows for future reference and supports geodatabases (Beyer 2009).
Empirical method
The Sum Line Lengths in Polygons tool (Figure 9) in the Analysis Tools toolset contained in the Hawth's Analysis Tools toolbox was used to calculate the total length of all contour lines (M) within each catchment, after which it was used as an input variable for Equation 2. The other input variables, area (A) and the contour interval (AH), were obtained from the relevant developed feature classes of the study area.
Neighbourhood method
A slope raster was generated from the raw DEM data using the Slope tool available from the Surface toolset contained in the Spatial Analyst Tools toolbox. The generated slope raster is based on a cell matrix approach, which represents the maximum change in elevation over the distance between the cell and its eight neighbouring cells, thus the maximum slope for each cell. The Zonal Statistics as Table tool in the Zonal toolset contained in the Spatial Analyst Tools toolbox (Figure 10) was applied on the slope raster to generate a summary table containing the statistical information about the input data or raster for a defined zone within the data frame, thus the average slope for each catchment (Figure 11). The slope raster was converted to a feature class (polygons) and reclassified into four slope frequency distribution classes, e.g. 0-3%, 3-10%, 10-30% and >30% as required by the deterministic flood estimation methods (SANRAL 2006; Van der Spuy & Rademeyer 2010) to establish the surface slope coefficients associated with different Mean Annual Precipitation (MAP) ranges. This conversion was done by using the Raster to Polygon tool in the Conversion Tools toolbox of ArcToolbox, while the Reclassify tool in the Reclass toolset contained in the Spatial Analyst Tools toolbox was used for the reclassification. The reclassified summary table is shown in Figure 12.
Length and average slope of main watercourses
The main watercourse in each catchment was manually identified in ArcMap. A new shape-file containing polyline feature classes representative of the identified main watercourse was created by making use of the Trace tool in the Editor toolbar. Each identified main watercourse was traced using the polyline feature classes of the 20 m interval contour shapefile as the specified offset or point of intersection, resulting in chainage distances between two consecutive contours. The attribute table of each shapefile was then edited by using the Add Field function to include the reduced heights of the contour intervals, and the length of each polyline was determined by making use of the Calculate Geometry function. These attribute tables (e.g. Figure 13) can then be exported to Microsoft Excel for further computations and used as input data for the deterministic and empirical methods used in design flood estimation.
Distance to catchment centroid
The centroid of each catchment under consideration was determined by making use of the Mean Center tool in the Measuring Geographic Distributions toolset contained in the Spatial Statistics Tools toolbox (Figure 14). Only the input polygon feature class representative of each catchment has to be selected to result in a point output feature class and associated attribute table representative of the x and y coordinate of the geometric centroid of each catchment (e.g. Figure 15). The length of the identified main watercourse in each catchment to a point opposite the identified centroid within the catchment was established by using the Measure tool in ArcMap. This measured length (LC) represents the distance along the main watercourse between the outlet and the point closest to the centroid of the catchment (e.g. Figure 15).
The results based on the methodology used during this study will now be discussed.
Projections and catchment geometry calculations
The frequency distribution of the altitude-above-sea-level classes present in the study area is summarised in Table 3 (a), while the slope-frequency-distribution classes based on the developed DEM (slope raster) are listed in Table 3 (b). The class-to-class variation and frequency distribution of the altitude-above-sea-level classes are indicative that the topography is relatively flat and that flood peaks will be attenuated and translated both in magnitude and duration respectively. The developed DEM for the study area is illustrated in Figure 16.
Average catchment slope
The results of the average catchment slope calculations based on the Neighbourhood method (DEM data), Grid method and Empirical method as used in the specific catchments, are listed in Tables 4 to 6. The scatter plots are shown in Figures 17 and 18. The developed DEM data was used as the baseline data for the evaluation of and/or comparisons with the two other methods.
According to Alexander (1990) there must be at least 50 grid points within a catchment, while Van der Spuy & Rademeyer (2010) suggested that the minimum number of grid points in catchments smaller or larger than 10 km2 must be 20 and 50 respectively. The number of grid points used varied from 50 to 7 200, with an overall average of 0,45 grid points per km2. The results indicated that either an increase or decrease in the number of grid points per km2 does not necessarily guarantee higher accuracies when compared with the Neighbourhood method (DEM data). For comparison purposes, the average catchment slopes (as %) for all the catchments were plotted as a scatter plot using the Neighbourhood method slopes against the Grid method slopes. The results are illustrated in Figure 17.
The Grid method underestimated the average catchment slope in all the catchments under consideration compared to the Neighbourhood method. The underestimation varied between 16,7% (0,48 grid points/km2) and 32,5% (0,34 grid points/ km2). Thus, if the DEM data based on the Neighbourhood method are accepted as true and accurate, then the average slope calculation using the Grid method with GIS-based input parameters must be increased with a value of between 17% and 33%. The inverse is also true. No definite relationship between the catchment area and these underestimations could be established.
The coefficient of determination (r2) of 0,88 is indicative of a high degree of association between the two methods. The Grid method is also useful for the development of slope frequency distribution classes used in the deterministic flood estimation methods. The Grid method is, however, time-consuming and sensitive to biased user input at different scale resolutions, extent of catchment areas and contour intervals used.
The results (Figure 18), based on the Empirical method (Equation 2), compared well with the Neighbourhood method. Since Equation 2 is a function of the catchment area (A), contour interval (AH) and total length of all contour lines within the catchment (Aí), the influence of each variable was evaluated. The results (Table 6) were indicative that there is only a direct relationship between A and A for slopes steeper than 4%, since flatter slopes will result in a lower contour density and associated M values. This trend was particularly evident for catchment areas exceeding 15 000 km2. The Empirical method underestimated the average catchment slope in all the catchments under consideration, except in catchment C5R005, where the average catchment slope result agreed with that of the Neighbourhood method.
M: A ratios of less than 1 500 resulted in an underestimation of between 20% and 30,2%, while M : A ratios between 1 700 and 2 750 were associated with underestimations between 18,7% and 0%. Thus, the higher the M: A ratios, the more accurate Equation 2 becomes. The coefficient of determination (r2) of 0,97 is also indicative of a high degree of association.
The visual comparison of results can be highly subjective. Therefore, the data pairs in each catchment under consideration were compared and evaluated using an array of conservation and regression statistics. Values of the y-intercept (a), slope (b), coefficients of efficiency (Ec) and determination (r2), which provide quantitative amplification of the results discussed above, are presented in Table 7.
The conservation statistics percentage differences in Table 7 reflect the differences between the average results as obtained with the Grid and Empirical methods compared respectively to the Neighbourhood method results. In both cases, the objective function (OF) is to minimise these percentage differences, of which the Empirical method's OF proved to be the minimum, with, on average, the underestimation limited to 14,3%. The y-intercept (a) and slope values (b) of the Grid and Empirical methods showed that these two methods could have different predictive abilities at flat and steep slope classes respectively. In the case of the Grid method, the positive y-intercept (1,01) is indicative of a possible overestimation of flatter slopes, while the slope value (b) which slightly exceeded unity (1,07), highlighted that the overestimation of steeper slopes is neither excluded nor impossible. The Empirical method's positive y-intercept value (1,58) highlighted that this method is even more likely to overestimate flatter slopes, while the slope value (b) less than unity (0,74) is associated with the underestimation of steeper slope classes.
Length and average slope of main watercourses
The main watercourse average slope results based on the Equal-area, 10-85 and Taylor-Schwarz methods are listed in Table 8, while the scatter plots are shown in Figures 19 to 21.
The degree of association between these methods was very high, since the coefficient of determination varied between 0,995 and 0,998. In the past, preference was given to the 10-85 method, since the Equal-area method is largely a graphical procedure and the use of the Taylor-Schwarz method is not widely known in South Africa.
Distance to catchment centroid
The results contained in Table 9 are indicative that the length of the watercourse to a position closest to the centroid (Lc) is influenced by the size and shape of the catchment, but more importantly, influenced by the average catchment slope. It is clearly evident from Table 9 that an increase in the average catchment slope is associated with a decrease in the Lc: L ratio, which varied between 0,48 and 0,62.
Projections and catchment geometry calculations
The DEM developed from the SRTM elevation data for southern Africa at 90 metre resolution proved to provide highly accurate raster information which can be used to calculate various catchment parameters (area, length and slope).
Average catchment slope
The developed DEM data based on the Neighbourhood method was assumed to be the most accurate representation of the actual average catchment slope and was therefore used as the baseline data to evaluate the Grid and Empirical methods. The Grid method underestimated the average catchment slope in all the catchments under consideration, while the results were indicative that either an increase or decrease in the number of grid points per km2 does not necessarily guarantee higher accuracies when compared with the DEM data. The use of at least 50 grid points in catchments up to 10 km2 is recommended; thereafter additional grid points at a grid density of 0,5 grid points/km2 in catchments up to a 1 000 km2 followed by 0,1 grid points/km^ in catchments exceeding 10 000 km2
The Empirical method also underestimated the average catchment slope in all the catchments under consideration, except in catchment C5R005, where the average catchment slope result agreed with that of the Neighbourhood method. The results were indicative that there is a direct relationship between the area (A) and the total length of all contour lines within the catchment (M).
The higher the M: A ratios, the more accurate the results calculated using the Empirical method.
Both the Grid and Empirical methods demonstrated high degrees of association with the DEM data and can be used along with suitable tools in the ArcGISTM environment to estimate the average catchment slope. The Grid method is especially useful for the development of slope frequency distribution classes, but the method is sensitive to biased user-input at different scale resolutions, extent of catchment areas and contour intervals used.
On the other hand, the Empirical method in its more rudimentary form (derived from first principles), in conjunction with standard functions in ArcGISTM, proved to be quicker and more accurate, while it is also very suitable for the development of slope frequency distribution classes. The higher accuracy was reflected by the higher r2 value (0,97) and the balance in tendency to either over- and underestimate the flat and steep average catchment slopes respectively. The results conclusively confirmed the preferential use thereof in conjunction with standard tools in the ArcGISTM environment.
Average main watercourse slope
The high degree of association between the Equal-area, 10-85 and Taylor-Schwarz methods proved that any of these methods can be used satisfactorily and with confidence in design flood estimation. However, this high degree of association between these methods does not necessarily guarantee the correctness thereof when used to estimate the time of concentration (Tc). In essence, the use of the average main watercourse slope as a suitable predictor variable for Tc estimation can only be justified when compared to Tc estimates based on the temporal distribution of rainfall (observed hyetographs) and runoff (observed hydrographs). In such a case, the validity of the established empirical relationship is also limited to the catchments or regions of original development.
Distance to catchment centroid
The average Lc: L ratio of 0,56 obtained from this study is indicative that the general assumption of using a Lc : L ratio of between 0,5 and 0,6 times the distance along the main watercourse is sufficiently accurate in most cases to be used in the various design flood estimation methods (Rademeyer 2012; Van der Spuy 2012). This is also a more definite guideline than the eyeball estimate thereof as proposed by Alexander (2001). However, practitioners are advised to evaluate each catchment individually using the tools available in ArcGISTM, before just using the proposed Lc : L ratios.
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Contact details:
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University of Stellenbosch
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Contact details:
Department of Civil Engineering
University of Stellenbosch
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JACO GERICKE has lectured in Hydrology, Irrigation and Water Engineering at the Centra University of Technology, Free State (CUT FS) for the past seven years. He has a special interest in flood hydrology, water resources management and hydrological modelling. He received the BTech Eng (Civil) and MTech Eng (Water) degrees from the CUT FS, and the BSc (Hons) Applied Science: Water Resources Engineering degree from the University of Pretoria (UP). He worked for six years at the Department of Water Affairs before joining the CUT FS. The results presented in this paper form part of his research towards the MSc Eng degree from the Stellenbosch University (2010).
DR KOBUS DU PLESSIS has lectured ir Hydrology, Water Engineering and Environmental Engineering at the Stellenbosch University (SU) for the past eight years. He has a special interest in water demand management and the implementation process as applied by municipalities. He served as a director in a municipal water division for seven years before joining the SU. After obtaining the B Eng (Civil) and M Eng (Water Resources Management) deg rees from the SU, he worked for the Department of Water Affairs, the City of Cape Town and the West Coast District Municipality. In 2011 he was awarded a PhD degree from the SU for his work done on ntegrated water management for local governance in South Africa.