You have three proposals for the same eroding bank. One is riprap, one is an articulated block mat, one is bagged armor. The prices are different, the scopes are different, and the low bid is not obviously the cheapest project.
This is the awkward case in procurement, because the systems are not interchangeable line items. Here is what to normalise before comparing.
We do not publish prices, so none of this is an argument for a number. It is a method for making three unlike proposals answer the same questions.
1. Is the temporary works in the price?
The single largest source of non-comparability on in-water work.
Ask each bidder: does this price include dewatering, diversion, or a coffer dam, and if so where is it?
Systems that need a dry working area carry a temporary works package that can rival the permanent works on some sites. Systems placed in flowing water do not. A comparison that puts the permanent works side by side and leaves temporary works as a provisional sum or a client risk is not a comparison.
Related: who carries the risk if dewatering proves harder than assumed?
2. Is the filter in the price, and is it specified?
Every permeable armor layer over an erodible bed needs an answer to the winnowing question described in why scour protection fails.
Ask: what goes between the armor and the bed, how is it specified, and is it in this price?
A bid that omits the filter is cheaper than one that includes it and will fail in a way that looks nothing like a cost saving. A bid that includes it but cannot say how it will be placed underwater has a different problem.
3. What is the assumed extent, and does it match?
Armor extent is a design output, not a preference. Different bidders working from different assumptions about scour depth, hole extent, or termination detail will price different quantities for the same problem.
Ask: what plan area and what termination detail is this price based on?
Then check whether the extents actually match. If one bidder has priced protection covering the computed scour footprint and another has priced the structure’s footprint, the second one is cheaper because it is a smaller job, not a better one. Bridge pier scour covers why those two areas differ.
4. What is the maintenance regime?
Ask: what does this need over twenty years, how often, and who does it?
The recurring cost in erosion control is re-work — replenishing migrated stone, repairing corroded wire, patching undermined slabs. A system that needs periodic replenishment is not worse for it, provided that cost is in the comparison rather than in a future maintenance budget nobody is looking at.
Ask each bidder for an inspection and maintenance expectation in writing. The differences between systems here are real and they are the reason lifecycle rather than first cost is the right basis.
5. What has each bidder assumed about permitting?
Ask: what approval path does this assume, and what is the programme if it takes longer?
Different systems have materially different permitting profiles. Dewatering is a regulated activity. New vertical structures draw more scrutiny than sloped protection in many jurisdictions. Work windows constrain when anything can happen in water.
A quote assuming an authorisation it will not get is not a cheaper quote, it is a delayed project. Permitting and agency approvals covers the approvals that recur.
6. What is the fill or material supply assumption?
Ask: where is the stone coming from and is the haul in this price?
For riprap, whether the local quarry actually produces the specified gradation. For bagged armor, where the fill stone comes from. For cast or precast systems, where the units are made and what the haul is.
Material supply assumptions are a common source of a price that moves after award.
7. What is the schedule, and what is the exposure while it runs?
Ask: how many days on site, and what is the site’s condition during that period?
Systems differ substantially in placement rate, and on an actively failing site the duration of the work is itself a risk. On tidal or emergency work with a short fixed window, a system that cannot be completed within the window is not a candidate regardless of price.
8. What does each one require of the subgrade?
Ask: what preparation does this need before the armor goes on?
Grading an irregular bed flat enough for a system that needs a regular bearing surface is a construction operation. If it is not in the price, it will be a variation.
9. What happens if it is damaged?
Ask: what does repairing a damaged section involve?
Incremental repair of individual units is a different proposition from replacing a section of a continuous or cabled system. This is not a decisive factor on its own; it belongs in the twenty-year picture.
10. What is not included?
The catch-all, and the most useful single question to put to all three bidders in writing.
Putting it on one page
A workable comparison sheet has a row for each of: permanent works, temporary works, filter, subgrade preparation, material supply and haul, plant and crew, site days, expected maintenance interval and scope, permitting assumption, and exclusions.
Fill it in for all three. The ranking usually changes, and where it does not, you can at least say why.
A note on our own position
Everything above applies to a bid from us as much as to anyone else. If you put those ten questions to us and to two competitors, that is the right process, and there are sites where the answers should send you elsewhere — when riprap is still the right choice and when a gabion is still the right answer set out where, and when not to use rock bags sets out what our own data does not cover.
Where to go next
- Cost, procurement, and specification for what drives installed cost
- The comparison hub for the system-by-system detail
- Permitting and agency approvals for the approval paths
- Design and sizing for what the extent calculation needs
If you want the questions above answered against a specific scope, send the drawings and the site conditions through the quote form.