Reservoirs and why hydrographic surveys matter

Across the UK and beyond, reservoirs are back in the spotlight: new assets are being planned, legacy assets are being re-evaluated, and operators are under pressure to prove capacity, safety, and environmental performance with hard data. In 2025 the UK government stepped in to accelerate delivery of major new reservoirs (the first in decades), granting “nationally significant” status to projects in East Anglia and Lincolnshire. Also in January 2026, Thames Water opened a major tender milestone for its proposed Abingdon reservoir, described as a nationally critical scheme and one of a wider pipeline intended to strengthen UK water security.

At the same time, an older challenge is becoming impossible to ignore: sediment.

Sedimentation steadily reduces usable storage, changes intake and spillway hydraulics, and can alter ecological conditions. What makes it tricky is that sedimentation is often uneven, meaning channels migrate, deltas form, and “known” volumes become assumptions.

A significant recent contribution to this issue is the Global Reservoir Inventory of Lost Storage by Sedimentation (GRILSS) dataset, published in Earth System Science Data, which compiles sedimentation and capacity-loss information for 1,013 reservoirs across 54 countries. That kind of work underlines a simple point: you can’t manage what you can’t quantify and in a reservoir, the truth is underwater.

That’s where hydrographic surveying comes in.

What is a hydrographic survey for a reservoir?

A reservoir hydrographic survey is a controlled measurement of the underwater environment, most commonly to create a bathymetric surface (the “underwater topography”) and derive:

• Accurate storage capacity / volume curves
• Sediment thickness and change (repeat surveys)
• Risk indicators near structures (intakes, spillways, scour zones)
• Navigation or operational constraints (where applicable)
• Dredging quantities and verification (before/after comparisons)

Modern programmes increasingly use multibeam echosounder (MBES) systems that capture dense depth measurements at speed, improving confidence compared with sparse single-beam lines. Recent industry announcements show how rapidly this technology is evolving smaller, higher-resolution systems and new deployment options are expanding where and how bathymetry can be captured.

When do you need a hydrographic survey?

Most reservoir owners and project teams commission hydro surveys when they face one or more of these triggers:

1. Capacity uncertainty – You need current, defensible storage figures for drought planning, supply resilience, or investment cases.
2. Sedimentation and asset performance – You suspect loss of volume, altered flow patterns, or reduced water quality performance.
3. Engineering works and compliance – You’re designing intakes/outfalls, refurbishing structures, planning dredging, or demonstrating environmental monitoring outcomes.
4. Change detection – You want repeatable evidence of how the reservoir bed is changing year to year.

Hydrographic data is also central in broader marine and nearshore monitoring programmes. Multibeam bathymetry is routinely specified to track geomorphological change, dredge areas, disposal sites, and scour around infrastructure. The same principle applies in a reservoir: when the bed moves, risks and costs move with it.

Where Survey Solutions adds value for Hydrographic Surveys

A hydrographic survey is only genuinely useful if it lands as a decision-ready output, that’s where Survey Solutions focuses: reliable data capture, tight controls, and clear deliverables that map to real-world decisions.

1) Survey design that fits the end use

We start with what the data must prove and build the method around it: Coverage, resolution, control, and QA expectations.

2) End-to-end field delivery

Reservoir projects rarely live entirely offshore. They involve access constraints, shoreline definition, tie-ins to existing assets, and integration with land surveys. We can combine hydrographic capture with the wider survey umbrella many projects need, such as:

• Topographic surveys of embankments, crests, spillways and compounds
• Control and setting-out support for construction or refurbishment
• GIS/CAD deliverables that slot into your design workflow
• Repeat monitoring programmes to quantify change over time

3) Clear, defendable outputs

We translate bathymetry into practical, auditable deliverables, typically including:

• Bathymetric surface + contours
• Cross-sections at critical locations (intakes, channels, deltas)
• Before/after comparisons (dredging or change detection)
• Survey report, metadata, and QA summary to support governance

4) A partner mindset

Hydrographic work often touches multiple stakeholders: Operators, designers, regulators, contractors. We aim to make the survey portion the “easy” part.

If you’re working on a reservoir scheme, new build, refurbishment, sediment management, or operational reassessment, Survey Solutions can help you get the underwater certainty you need and integrate it with any land and project survey services that keep programmes moving.

If you’d like to talk through your reservoir or hydrographic survey requirements, get in touch below.