Alex Lipp
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alexlipp.github.io
Alex Lipp
@alexlipp.github.io
Lecturer in Earth Sciences @es-ucl.bsky.social | Interested in rivers, mud, mountains, pollution, carbon cycling, quantitative methods, open science | alexlipp.github.io | www.sewagemap.co.uk | he/him | 🌍 🌱 🏔 🧗‍♂️ 🏕 🏃‍♂️
This was a very fun project to work on, with some neat stats & maths from fractals to fluid mechanics. We were surprised that for such a high profile dataset like sewage spills there had been such limited public statistical analysis until now! 💩 🧮 🧑‍💻

eartharxiv.org/repository/v... 8/8
December 11, 2025 at 7:52 AM
This matters because water companies now need to create hydraulic models of thousands of CSOs to reduce their spilling… but unless they can model infiltration (hard!) they are likely to underestimate the frequency of the most damaging, long duration spills! 7/
www.gov.uk/government/p...
How to form, publish and maintain your drainage and wastewater management plan (DWMP)
www.gov.uk
December 11, 2025 at 7:52 AM
What causes the heavy tail? When trying to replicate it using hydraulic models we can only do so by including infiltration of groundwater into pipes through cracks… this suggests that these long duration spills are *not* only occurring after heavy rain…

eartharxiv.org/repository/v...

6/
December 11, 2025 at 7:52 AM
We think this is driven by daily fluctuations in water usage (🚿 💩) which modulates the length of sewage spills…

eartharxiv.org/repository/v...

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December 11, 2025 at 7:52 AM
A total (and cool 🤓) surprise for us, was the discovery of a periodic variation of the misfit to this modelled trend, fluctuating around spills that are multiples of 24 hours long… what’s causing this?

eartharxiv.org/repository/v...

4/
December 11, 2025 at 7:52 AM
Statistically, this tail is well described by a stretched exponential distribution. It’s not quite as heavy as a power law, but much heavier than a vanilla exponential…

eartharxiv.org/repository/v...

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December 11, 2025 at 7:52 AM
We find that sewage spills follow a very heavy-tailed distribution. 10% of spills account for 85% of all spilling *time*. So, it’s not the infrequent, short spills we should care about, it’s the infrequent long ones…

eartharxiv.org/repository/v...

2/
December 11, 2025 at 7:52 AM
Is this all subjects? Undergrad & postgrad?
November 28, 2025 at 4:22 PM
I mean c’mon you’re the CEH! You famously study things that are naturally messy and green and blue! Why opt for…. black with very hard lines?!
October 16, 2025 at 11:27 AM
so pleased everyone is choosing such unique and distinctive typefaces
October 16, 2025 at 11:27 AM
Finally, the scientific models used by agencies to model nutrient pollution are _remarkably_ opaque and under scrutinised given their ubiquitous importance (as I have written about previously: alexlipp.github.io/posts/2024/0...)
Greater transparency is needed on water quality modelling in the UK - written evidence to Environmental Audit Committee
The following was submitted by myself and Dr Gareth Roberts as written evidence to the Environmental Audit Committee’s non-inquiry session into water quality, published here. We highlight that computa...
alexlipp.github.io
September 27, 2025 at 10:05 PM
also the population change assumes (iirc) its all *new* population into catchment, rather than say residents moving *within* catchment (=no net increase). so, population density increasing due to limited supply would be a “win” for nutrient neutrality…
September 27, 2025 at 10:05 PM
you’re right on the gist (nutrient neutrality is mad) but actually population growth *is* linear with nutrient outflow (ie it’s not a capacity thing). Problem is builders can’t pay to increase treatment efficiency at existing plants (!?) even though that can work…
September 27, 2025 at 10:05 PM
The perfect conditions continue 😎 🌞!
September 6, 2025 at 8:50 AM
… and blessed with some Aurora Borealis too! #studygeologyandseethenorthernlights
September 5, 2025 at 5:11 PM
Focus on "universities" raising fees misses the point that the real injustice is the interest rates & repayment thresholds on student debt which I suspect plays greater role in determining how much is paid over a lifetime than the initial "up-front" fees...
August 15, 2025 at 9:33 AM
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August 11, 2025 at 2:20 PM