What is a cm of Water Worth?

What Is a Centimetre of Water Worth?

When a river becomes shallower, the first consequence for freight is physical: a vessel may no longer be able to carry the same load safely. The economic consequences follow from what the operator has to do about that. The same cargo may need more sailings. Limited departure capacity may become more valuable. Freight may move to another route or mode. If an operating restriction becomes binding, part of the original route may stop being available altogether.

This is why a small physical change can produce very different economic effects. During the 2018 drought, regional evidence for the IJssel and Twentekanalen recorded months of reduced vessel loading, additional movements and some substitution to road transport. In September 2026, Rijkswaterstaat announced one-way operation on part of the Boven-IJssel as low water narrowed the navigable channel. The restriction did not close the entire river, but it changed which movements were permitted. [1]

Those observations lead to a more useful question than simply asking whether water is scarce: when does one additional centimetre of usable navigable depth actually change the cost of moving freight? Our answer is that there is no universal euro value for a centimetre. In an illustrative freight model, an extra centimetre can reduce allocated transport cost by about €250, produce a €3,000 saving when departure capacity is binding, generate a conditional €21,760 benefit if route access is restored, or produce no immediate saving at all. The centimetre is the same size in every case. What changes is the constraint it relaxes.

Start with the freight problem, not the number on the gauge

It helps to separate three quantities that are easy to blur together. A gauge reading is a water-surface elevation relative to a reference level. Navigable depth is the distance between the water surface and the relevant bed or obstruction. Vessel draft is how far the vessel extends below the waterline. The freight problem depends on the controlling navigable depth along the route because that depth can limit the vessel's usable draft and therefore the amount of cargo it can carry. [2]

The distinction is practical, not pedantic. A higher gauge reading at one location does not automatically give a vessel another centimetre of usable draft over an entire journey. Another section may remain shallower. The vessel may already be at its loading limit. Or an operating rule may still prevent the movement. An extra centimetre has value only when it changes a constraint that matters to the actual transport decision.

That same logic explains why the model is built around a fixed freight task rather than around a river-wide traffic total. The report asks what happens to the cheapest way of delivering 10,000 tonnes during a planning period when navigable depth changes. The period is not assumed to be one day, and the 10,000 tonnes are not presented as observed IJssel traffic. They are a controlled quantity that allows the transport choices to be compared consistently. [2]

When the shallow-water route is available, the shipper can use it. Freight that cannot be carried there can use an alternative transport option. In the illustrative setup, another centimetre adds ten tonnes of payload per departure until the vessel reaches its loading limit, up to 20 departure-equivalents are available, and the alternative costs €15 per tonne. Those inputs are not a prediction of one operator's behaviour. They create a transparent experiment: hold the freight requirement fixed, let the shipper adjust, and observe what the extra centimetre changes. [3]

The same centimetre can do three different jobs

At a depth of 2.50 metres, the illustrative vessel can carry 1,500 tonnes. At 2.51 metres it can carry 1,510 tonnes. If departure capacity is still available, those extra ten tonnes per movement mean the same 10,000 tonnes require slightly less aggregate movement capacity. In the continuous model, that reduces allocated transport cost by about €250. [3]

The important point is what has changed: utilisation has improved, but no other constraint has become binding. That is also why the €250 should not be read automatically as cash saved on the next individual shipment. In the report's whole-trip check, 10,000 tonnes still requires seven movements at both 2.50 and 2.51 metres, costing €39,634 in either case. Better utilisation can have an economic value before it eliminates an indivisible voyage.

At 1.45 metres, the system looks different. The illustrative payload is only 450 tonnes per departure, and all 20 available departures are already being used. Those departures move 9,000 tonnes, leaving 1,000 tonnes to the alternative option. Now the next centimetre cannot create value merely by reducing the amount of movement capacity used, because there is no spare departure capacity to rearrange. Instead, it makes each of the existing departures more productive.

At 1.46 metres, the extra ten tonnes on each of 20 departures creates room for another 200 tonnes on the shallow route. Those 200 tonnes no longer need the €15-per-tonne alternative, so the saving is €3,000. [3] The physical increment is still one centimetre, but the economic mechanism has changed from marginal utilisation to relief of a binding capacity constraint.

The third case is different again because the set of available transport choices changes. Below the assumed threshold, the model treats the relevant direction of the route as unavailable, so all 10,000 tonnes use the alternative and cost €150,000 to move. If a change from 1.44 to 1.45 metres also restores route availability, the optimised transport cost falls to €128,240. The conditional difference is €21,760. [3]

That larger number does not mean the "last centimetre" of water has suddenly acquired an intrinsic price of €21,760. It reflects a change of operating regime. The model has moved from a state in which the route is unavailable to one in which it can be used. Rijkswaterstaat's published restriction trigger does not establish that adding exactly one centimetre automatically produces that reopening, so the €21,760 figure is deliberately conditional on access actually being restored. [1]

Scarcity alone does not determine value

It is tempting to conclude that another centimetre simply becomes more valuable as water becomes scarcer. The model shows why that rule is too simple.

Suppose the alternative transport option costs €10 per tonne instead of €15. Under the illustrative assumptions, that alternative is already cheaper than the restored shallow-water route around the threshold. Making the river route available again therefore produces no transport-cost benefit for this freight problem. [4] The physical option has returned, but it is not the economically preferred option.

A similar problem arises with bottlenecks. If another reach remains equally shallow, improving one location may add no usable draft over the complete route. Improving both locations can have value even when improving either one in isolation does not. The useful unit is therefore not "a centimetre somewhere on the river", but a feasible route through the network.

Time matters too. A centimetre of additional depth available for one afternoon is not equivalent to one maintained through a long low-water episode. Freight requirements, inventories, vessel cycles and the capacity of alternatives can all change over the period. The value has to be evaluated against those changing choices rather than obtained by multiplying the largest one-centimetre result by every day of drought. [5]

These are not qualifications added after the interesting numbers. They are the economic result. Capacity has value when it changes a decision that matters; scarcity by itself does not tell us how large that value is.

What the model tells us, and what it does not

The transport-cost curve is useful because it makes the mechanism explicit. It tells us when additional depth changes payload, when a departure constraint becomes valuable, when an alternative mode caps the benefit and when an access change creates a discrete jump. That is already enough to improve how low-water infrastructure problems are framed.

It is not, however, a complete social valuation of water. A shipper's transport cost is only one part of a broader appraisal. A real intervention would also require evidence about hydraulic effectiveness, environmental effects, other water uses, congestion or emissions on alternative modes, the duration of the benefit and the cost of producing or maintaining the additional navigable depth. A centimetre of navigable depth is not itself a cubic metre of water, and the model does not identify a preferred engineering intervention. [5]

Nor does the model estimate the observed daily economic loss on the IJssel. Doing that would require data on actual freight demand, vessel loads, origins and destinations, route choices, operating capacity and the timing of restrictions and reopening. The 10,000-tonne problem is useful precisely because it separates the mechanism from those missing empirical quantities.

So what is a centimetre of water worth? The defensible answer is not a single number. It is worth the cost of the constraint it actually relaxes, for the freight and period in which that constraint is binding. Sometimes that is a small utilisation gain. Sometimes it is the value of scarce capacity. Sometimes it is the benefit of regaining an economically useful route. And sometimes the extra centimetre changes nothing at all.

Research note. These are illustrative transport-cost scenarios per 10,000-tonne planning period, in 2024 euros, not measured daily or IJssel-wide losses. The €21,760 example requires an assumed restoration of route access. The model does not establish the complete social value of water or identify a preferred intervention.

Explore the research

The technical report develops the depth-to-payload relationship, transport alternatives, departure constraints and route-access scenarios. The accompanying IJssel Depth Value Model contains the calculations and sensitivity tables behind the examples.

Sources and research

[1] Operating/historical context: RWS 24 September restriction; RWS 11 September trigger notice; 2020 IJssel/Twentekanalen drought study.

[2] Depth/model boundary: RWS restriction notice and MGD definition; Rokin report Sections 2-3 + IJssel model.

[3] Inputs/results: KiM 2026 freight-cost update; KiM/Panteia inland-shipping tables; Rokin report Section 4 + model.

[4] Mechanism/substitution: Jonkeren et al. 2007; Jonkeren et al. 2011; Rokin report Section 5 + model.

[5] Welfare/appraisal limits: CPB/PBL CBA guidance; RWS mobility-effects guidance; Rokin report Sections 6-8.