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May
3
Thu
The 35th Annual Alexander Graham Christie Lecture
May 3 @ 3:00 pm – 4:00 pm
The 35th Annual Alexander Graham Christie Lecture @ 210 Hodson Hall

Heidi Nepf, the Donald and Martha Harleman Professor of Civil and Environmental Engineering at the Massachusetts Institute of Technology, will deliver the 35th Annual Alexander Graham Christie Lecture.

The lecture will be held at 3 p.m. on Thursday, May 3, in 210 Hodson Hall.

 

How vegetation alters waves and current, and the feedbacks to environmental system function

Vegetation provides a wide range of ecosystem services valued at over 4 trillion dollars per year. Seagrasses, salt marshes, and mangroves, damp storm surge and waves, mitigate anthropogenic nutrient loads, and provide important habitat and blue carbon reservoirs. The conservation and restoration of these landscapes has become the center-point of nature-based solutions for coastal protection and carbon mitigation. This seminar will summarize basic concepts in vegetation hydrodynamics, focusing on flexible meadows of seagrass, for which the bending of plants in response to fluid motion (called reconfiguration) plays an important role in setting the drag. Scaling laws are developed to describe the damping of currents, turbulence and waves as a function of plant morphology, flexibility, and shoot density. The feedbacks from plant-flow interaction to sediment transport and carbon sequestration are also discussed.


Sponsored by the Department of Mechanical Engineering and the JHU Student Section and the Baltimore Section of the American Society of Mechanical Engineers.

Nov
6
Tue
2018 Charles and Mary O’Melia Lecture in Environmental Science
Nov 6 @ 3:00 pm – 4:00 pm

Re-Envisioning Wastewater Treatment for the 21st Century

Desmond LawlerDesmond Lawler, PhD
Nassir I. Al-Rashid Chair in Civil Engineering
Professor
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin

Abstract: The philosophy of municipal wastewater treatment has changed only slowly in the past 100 years. From approximately 1920 to 1970, a wastewater discharge was considered acceptable if the dissolved oxygen level in the receiving stream did not dip below 5 mg/L downstream of the discharge. Protecting aquatic life, particularly fish, from immediate death due to low oxygen levels was the primary motivation and the goal. The passage of the Clean Water Act in 1970 reflected a broader view to include concerns about eutrophication by nutrients and ecological and human health concerns with the naming of “priority pollutants.” Nevertheless, the central concept was that discharge concentrations would be acceptable if they took advantage of the assimilative capacity of receiving waters; that is, if they limited the harm to acceptable values. Now we are embarking on a new philosophy, captured by the phrase “One Water” by the Water Environment Federation, in which we think of wastewater not as a problem for disposal but as a resource.

Why is this shift in philosophy happening? At least two major changes have occurred since the old philosophies were developed. First, a dramatically increased population has led to a substantial increase in “indirect potable reuse” of wastewater, whereby the effluent discharge from one city is a part of the drinking water source for a downstream city. In many areas of the arid Southwest, that “part” can often be nearly 100%. An extension of this trend, due to water shortages, is the drive toward direct potable reuse of wastewater. Second, not only do the chemical and pharmaceutical industries now produce tens of thousands of synthetic chemicals that were not dreamed of when the “priority pollutant” list associated with the Clean Water Act was developed, we now understand that some of these products are endocrine disruptors and others lead to microbial antibiotic resistance.

In this talk, I will try to make the case that wastewater treatment needs to be changed, perhaps radically, to reflect the new philosophy and to meet the needs of the 21st century. The thrust of the presentation will be to explore some possibilities for these radical changes and try to back them up with preliminary engineering calculations.

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