Infiltration practices and low impact development
I’d like to commend you on your magazine’s coverage of stormwater management issues and methods of mitigating stormwater impacts. This is truly a hot topic, and design professionals need all the information they can get on this subject. However, after reading the Low Impact Development (LID) article in your July issue (page 28), I must comment. While I know your publication and the authors of the articles are well intentioned, I’m afraid that the article may be adding to the growing body of misinformation surrounding infiltration practices.
First, "Tc" and "CN" are simply parameters developed by Victor Mockus, the father of the SCS cover complex method, as average transformation parameters to convert rainfall to runoff volume in true watersheds. This methodology was never intended to be used to micro-analyze small land development sites. Unfortunately, it is one of the only tools available for the analysis of development-scale hydrology.
The casual use of "Tc" and "CN" in the article inappropriately suggests that these parameters represent a true measure of hydrologic process, which they don’t. If we are truly to mitigate impacts from land development activities, it is critically important that we, as design professionals, understand true site hydrologic process, and the foundation and limitations of our design tools.
While LID and infiltration practices are important tools for the mitigation of flow peak, volume, and water quality impacts from land development activities, it is wrong to suggest that these techniques can be used to mimic or replicate existing site hydrology. Site hydrology is an extremely complex interaction between rainfall, topography, soils, plants, and local geology. This process also is extremely variable from season to season. As soon as you remove the first blade of vegetation or move the first spade of dirt on a site, the complex site hydrologic balance is altered forever. We can only hope to mitigate the impacts to some degree.
By implying that we can mimic the process, we are only misleading the lay community, just like we did in the late ’70s and ’80s when we said that detention basins would solve our urban runoff problems.
And what about potential impacts from inappropriate design or location of infiltration facilities? Managing the increased runoff volume through the use of bio-cells and other infiltration facilities usually results in a significant increase in localized loading rates to the subsoil. In the natural condition, about 60 percent (an average value for the eastern United States) of the water infiltrated at the surface is used by plants, or evaporated at the surface (evapotranspiration or ET). The remaining 40 percent makes it to the sub-soil. The use of subsurface infiltration facilities puts the entire infiltration volume into the subsoil, effectively doubling the natural loading on an acre-foracre basis.
However, some "experts" suggest that infiltration facilities can be designed for a 5:1 loading based on tributary area. Given the loss of the natural ET component, these suggested loading rates result in a 10:1 effective overloading of the subsoil. Is this replicating natural hydrologic processes? Of course not. While some soils and local geologic conditions may accept these high subsoil loading rates, many will not.
And what are the potential impacts? To date I’ve seen wet basements, foundation failures, hill-slope failures and slides, and down-gradient surface seeps, which have impacted the use of off-site land areas. As design professionals we must understand the science and be cautious of what we aren’t sure of.
I suggest that your publication balance it’s reporting by including articles on developmentscale hydrologic and infiltration processes, and cautions related to over-infiltration. There is a true lack of knowledge and expertise in these areas in the design profession.
Scott A. Brown, P.E.
University Park, Pa.
Hiring and motivating talented employees
I enjoyed reading your "Dog Days of Summer" column in the July 2004, issue of CE News (page 6). I wanted to share with you a few thoughts on compensation and motivation.
If we want to help civil engineering managers improve their operations, we need to help them understand and fulfill the top five employee motivators—1) interesting work; 2) involvement in decisions; 3) feedback; 4) training; and 5) respect.
If we want to reinforce the preconceived notion of what motivates employees, we should emphasize the employees’ bottom five motivators—6) salary; 7) bonuses; 8) vacation; 9) retirement; and 10) other benefits and perks.
Engineering managers make a huge mistake when they think pay and annual bonuses impact their employees on a day to day basis.
In fact, bad employees may be convinced to stay, while great employees may be convinced to go elsewhere. Employees should be motivated by the jobs they do, and their bonuses should be the reward for meeting corporate and individual goals.
When managers hire for talent and reward for achievement, motivational problems disappear.
The hard part for engineering managers is to identify the talents of job applicants.
Resumes and interviews do not identify an applicant’s talents, and talent must be hired because talents cannot be imparted or acquired after the hire. Engineers need to know how to identify and measure talent.
Employers often try to hire for attitude, but that usually means the applicant said the right things, laughed at the right times, and agreed with what the interviewer said or suggested.
Talent is not attitude, but rather is specific behaviors, coupled with the appropriate interests, and supported by adequate thinking styles.
Employers generally over-rely on the interview and qualifications. The goal should be to hire competent people, not necessarily the most competent, who will become successful employees. The best I can tell, a resume never actually does any work.
Managers usually are quite surprised when they learn that their best employees are not their brightest employees. I guess that speaks to the efficacy of hiring the best and the brightest.
Robert F. Gately, MBA, P.E.
I contend that most [civil engineers] don’t fully grasp our value to society. It is difficult to promote something that you don’t understand.
How do you quantify that value? Who would believe that we contribute so much? At the same time, when you start talking about those kinds of dollars, you should begin to get a sense for why there is an effort to reduce those costs. The cost of engineering on a macro level, in just this country, is frightfully large.
Anywhere you have that size number, there are going to be folks trying to get or retain a little piece of that pie for themselves.
Engineers should continue to be challenged.
[The P.E. exam] challenged me to re-learn skills and to re-think some unsound practices that I had fallen into. It challenged me to be more professional in my conduct as an engineer. To put some teeth into the continuing education effort would effect the same challenge.
Currently, the biggest challenge is to just find the number of hours needed. There is little academic challenge to most of the training that we get. What value does that bring?
Max Broome, P.E.
As engineers, we need to do better at marketing our services and showing where we add value to the project. Otherwise, we’ll always be considered a commodity to be purchased at the lowest possible cost.
In addition, we need to acknowledge the fact that outsourcing is here to stay. Clearly, there are some routine services that can be outsourced effectively. Outsourcing can improve the competitveness of an engineering firm, improve schedules, and save the client money.
Outsourcing also can help an engineering firm manage its staff levels during boom and bust cycles. It can free up engineers to provide personal service to a client and to spend time on creative solutions to previous problems. This can help enhance the image of the engineering profession. Overall, I think we need to start looking at the glass as half-full instead of half-empty when it comes to outsourcing.
Ric Slocum, P.E.