Alluvium
Alluvium is loose soil or sediments (such as clay, silt, sand, gravel and so on) that is eroded and carried in suspension by flood or river water before being deposited. The material of alluvium is may be unconsolidated, i.e. not formed together into solid rock, and can by picked up or eroded and carried away by moving water before being deposited elsewhere when the water flow slows down. Where the loose alluvial material is consolidated into a stone-like material (or lithological unit), this is known as lithification.
The fine-grained fertile soil that is deposited by water that flows over flood plains or river beds is known as alluvial soil.
Some of the characteristics of alluvial soils include:
- The soil morphology will vary according to the age of the alluvial deposit and how it was formed.
- The textural range of the soil can vary widely from gravel to silty clay.
- Drainage can vary from very poor to free.
- The texture of the soil can vary both vertically and laterally.
- It may contain a large amount of organic matter.
The presence of alluvial deposits may mean that the ground conditions are poor and so can require the construction of a raft foundation, or deep pile foundations. In these conditions, strip or pad foundations would require significant excavation.
Geoarchaeology, Using Earth Sciences to Understand the Archaeological Record, published by Historic England in 2015, defines states: ‘alluvium any water-borne sediment is technically alluvium, but the common usage is for fine-grained floodplain deposits’.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Cutting carbon, cost and risk in estate management
Lessons from Cardiff Met’s “Halve the Half” initiative.
Inspiring the next generation to fulfil an electrified future
Technical Manager at ECA on the importance of engagement between industry and education.
Repairing historic stone and slate roofs
The need for a code of practice and technical advice note.
Environmental compliance; a checklist for 2026
Legislative changes, policy shifts, phased rollouts, and compliance updates to be aware of.
UKCW London to tackle sector’s most pressing issues
AI and skills development, ecology and the environment, policy and planning and more.
Managing building safety risks
Across an existing residential portfolio; a client's perspective.
ECA support for Gate Safe’s Safe School Gates Campaign.
Core construction skills explained
Preparing for a career in construction.
Retrofitting for resilience with the Leicester Resilience Hub
Community-serving facilities, enhanced as support and essential services for climate-related disruptions.
Some of the articles relating to water, here to browse. Any missing?
Recognisable Gothic characters, designed to dramatically spout water away from buildings.
A case study and a warning to would-be developers
Creating four dwellings... after half a century of doing this job, why, oh why, is it so difficult?
Reform of the fire engineering profession
Fire Engineers Advisory Panel: Authoritative Statement, reactions and next steps.
Restoration and renewal of the Palace of Westminster
A complex project of cultural significance from full decant to EMI, opportunities and a potential a way forward.
Apprenticeships and the responsibility we share
Perspectives from the CIOB President as National Apprentice Week comes to a close.
The first line of defence against rain, wind and snow.
Building Safety recap January, 2026
What we missed at the end of last year, and at the start of this.