Podcast Summary

Episode Overview

Podcast: New Books Network
Host: Kelvin Vu
Guests: Rob Holmes & Brett Milligan (with Gina Worth as co-author, not present)
Book Discussed: Silt Sand Slurry: Dredging, Sediment, and the Worlds We Are Making (Applied Research & Design, 2023)
Date: December 11, 2025

This episode dives into the practice, science, and cultural politics of dredging and sediment management as explored in the book "Silt Sand Slurry." Co-authors Rob Holmes and Brett Milligan, both landscape architecture professors and founding members of the Dredge Research Collective (DRC), join the podcast to outline how sediment is not just waste, but a potential resource, and to advocate for a more nuanced, engaged, and design-minded approach to shaping our watery landscapes.

Guest Introductions & Professional Backgrounds

[01:30–04:55]

• Rob Holmes: Leads the Landscape Infrastructure Design Lab at Auburn University, focuses on nature-based infrastructure, especially in coastal and riverine settings. Currently, projects engage the community in Charleston and work with the Army Corps to create a new island off the Georgia coast.

  • "Siltsand Slurry, in a lot of ways, is kind of the story of how we got there. And...a theory of landscape making that underlies a lot of the current work." [03:34]

• Brett Milligan: Directs the Metamorphic Landscapes Lab at UC Davis, with work centered on climate adaptation, especially in the California Bay Delta. His work questions and expands the boundaries of landscape architecture’s skill set in sedimentary settings.

What Are Dredging & Sediment? Why Do They Matter?

[04:55–07:31]

• Rob Holmes:
  • Dredging: The underwater removal of sediments, which can be for clearing navigation channels (removal) or obtaining material for landscape creation (beaches, marshes, islands).
  • The true value is not the mechanical action itself, but the landscapes and ecological, social, and cultural benefits produced.
  • "One of the kind of key currencies of climate adaptation is sediment itself..." [07:17]

The Dredge Research Collective (DRC)

[07:31–10:42]

• Brett Milligan:
  • DRC emerged from curiosity about "soft systems" in landscapes and the massive human manipulation of sediment, surpassing natural geological processes.
  • Progressed from exploratory/documentary efforts (Dredgefest events, comparative studies of regions) to actual design and advocacy projects across the US.
  • Dredgefest events brought together regulators, engineers, scholars, and designers to instigate dialogue.

From Waste to Resource: Rethinking Sediment

[10:42–14:49]

• Rob Holmes:
  • The shift towards recognizing sediment’s value requires deep systemic changes at both individual and institutional levels.
  • Environmental regulations are often based on the mid-20th century idea of sediment as a contaminant, ignoring opportunities for beneficial use.
  • "Regulations...center around the idea of sediment as a contaminant... aimed at preventing negative consequences...not necessarily looking for the kind of benefits..." [12:22]
• Brett Milligan:
  • The real "problem" is the entrenched system and culture; advocating for more intelligent, choreographed, and foresighted sediment management.

The Flawed Logic of Cost-Benefit Analysis

[14:49–20:47]

• Kelvin Vu: Quotes the book: "The elements of the problem are the elements of the solution."
• Brett Milligan:
  • Standard cost-benefit analyses are reductive, exclude environmental/social costs, and prioritize short-term quick fixes ("Highly reductive and...self serving in how the equation is set up..." [16:12]).
  • Long-term inefficiencies are often ignored.
• Rob Holmes:
  • Cost-benefit is falsely valorized as objective and apolitical; converting ecological/social values into economic terms inherently loses nuance and depth.
  • There’s progress: The Army Corps is shifting toward beneficial use objectives, raising their targets (e.g., “70 by 30”—70% beneficial use by 2030).

Choreographing Sediment: A New Design Metaphor

[23:16–26:58]

• Brett Milligan:
  • "It really is sort of a dance with landscape rather than a command control approach..." [24:11]
  • Choreography acknowledges many actors—human, non-human, regulatory, ecological—working together in time. It’s about guiding, not controlling, landscape change.
• Rob Holmes:
  • Choreography requires openness, observation, and ongoing adjustment: "Choreographer and dancer are in a back and forth relationship...the work can actually be much better, much richer, lead to better results if it acknowledges and works with that difference." [25:43–26:58]

Collaborative Authorship and Multivocality

[27:31–33:05]

• Rob Holmes:
  • The book took years to develop, with writing interspersed with experiments and design competitions (e.g., Public Sediment project).
  • Collaboration, while occasionally tense, enriched both the process and the final product.
• Brett Milligan:
  • Multiple voices and entry points: interviews, visual essays, reflective writing, and expository chapters all present different ways to explore sediment.
  • "You don't have to read it sequentially...You can just go look at an interview or...the technology chapter. It's kind of designed in a way that you can, you know, find your own entry point." [31:03]

Time, Change, and Landscape Inertia

[33:49–38:21]

• Rob Holmes:
  • Different systems (ecological, regulatory, design) operate at different rates and resist change ("inertia").
  • In projects like Public Sediment, instead of solving the problem for all time, they focused on "changing the trajectory" and working on achievable timescales (20–30 years).
  • "Buying two decades of time, three decades of time is very significant. A lot happens in 20 years." [37:24]
• Brett Milligan:
  • "Time is plural...Just this unified notion of time does not really apply in the landscape." [37:31]

Democratizing Sediment: Dredgefest, Sediment Publics, and Aesthetics

[39:50–46:03]

• Rob Holmes:
  • Dredgefest was a series of events to help the DRC and wider audience understand and experience sediment’s worlds. They initiated dialogues between unlikely pairs—engineers, regulators, and writers.
• Brett Milligan:
  • Sediment publics: Efforts to build broader awareness and engagement with sediment issues—making invisible, technical, or regulated worlds accessible and relatable.
  • Accessibility is fundamental: sediment’s underwater or granular state, technical language, and professional silos obscure it from public awareness.
  • Designers can play a vital role in creating access, visibility, and public connection to these landscapes.

Landscape Architecture's Role: Challenges and Futures

[46:03–50:57]

• Kelvin Vu: Notes that sediment is generally outside traditional landscape architecture curricula.
• Brett Milligan:
  • Landscape architecture is facing a tough moment: concern for profit is eclipsing sustainability. Regulatory rollbacks, automation, and shifting political landscapes pose challenges, but also calls designers to action.
  • "It's a really, really...scary and interesting time from a design perspective...What actually matters is a really hard introspective question." [47:28]
• Rob Holmes:
  • Despite growing challenges, the book’s core arguments endure: nuanced engagement, collaboration, and public constituency-building are critical.

Looking Ahead: Current and Future Work

[51:15–54:57]

• Rob Holmes:
  • Ongoing work includes the Tidelens project (with Auburn, UVA, Penn labs) to refine tools for designers to work more effectively with sediment as a medium for climate adaptation—involving island creation, modeling, and tool development.
• Brett Milligan:
  • Working on "Just Transitions in the Delta," a participatory scenario planning project addressing sea level rise and salinity intrusion in California’s Delta. Emphasis on public engagement, transdisciplinary thinking, and learning from failures as well as successes.

Book Recommendations

[55:04–57:47]

• Rob Holmes:
  • Floating Coast by Bathsheba Demuth – Environmental history of the Bering Strait, exploring human, animal, and ecological histories under different political regimes.
• Brett Milligan:
  • Battling the Inland Sea by Robert Kelley – On the terraforming and flood control history of California’s Central Valley.
  • The Future is Degrowth: A Guide to a World Beyond Capitalism – As a counterpoint to current socio-political trends.

Notable Quotes & Timestamps

• "Dredging is a clarifying act. It reveals how people intervene in the material flow and deposition of sediments..." —Kelvin Vu quoting the book [04:55]
• "Regulations...center around the idea of sediment as a contaminant...not necessarily looking for...benefits." —Rob Holmes [12:22]
• "Highly reductive and...self serving in how the equation is set up." —Brett Milligan on cost-benefit analysis [16:12]
• "It really is sort of a dance with landscape rather than a command control approach..." —Brett Milligan on 'choreographing sediment' [24:11]
• "Time is plural...Just this unified notion of time does not really apply in the landscape." —Brett Milligan [37:31]
• "Sediment publics is really trying to build constituency around understanding, experiencing the importance of sedimentary landscapes." —Brett Milligan [44:39]

Memorable Moments

• The origin story of the DRC and their transition from amateur explorers to advocates and designers of sedimentary landscapes.
• The challenging but productive experience of multi-disciplinary, multi-author collaboration.
• The metaphor of "choreographing sediment" as a new model for adaptive, participatory, and responsive design.
• Reflections on adapting design practices to plural timescales, increased uncertainty, and the pressing realities of climate change.

Conclusion

This episode is both a rich introduction to the world of sediment and an exploration of how systemic change at both cultural and institutional levels can enable more adaptive, inclusive, and hopeful landscape futures. Holmes and Milligan make a compelling case for designers to take a leadership role in shaping public understanding and stewardship of sedimentary environments, and to do so through humility, collaboration, and attentiveness to the dynamic and plural nature of both landscapes and time.