The hundred million dollar question is “Will the Waimea Dam hold water or have we built a $200 million bridge?”

In the December 2022 update Mike Scott CEO of Waimea Water, the dam construction company, tells us that we are still on budget but the budget is being stressed by various items such as the cost of the Mechanical & Engineering components that were never designed or priced in the original quote. Makes you wonder how we ever had a “P95” guarantee doesn’t it?

However, this has also been the story told to Council in the past. We are on budget but there are pressures. Nek Minnut a $30 million blow out. Never saw that coming! Not the first time, not the second time, not the third time. And yet here we are $195 million versus the P95 price of $76 million.

The dam is now about 84% complete as compared to the 75% complete at the last two updates. Because it 75% complete in the first update early in 2022 and then again 75% complete in the mid year update we discovered that the update percentage figure is tagged to the timeline and not the amount of work done. So, because the completion timeline was pushed out in the midyear update the percentage completed remained the same. We have now revisited the practical completion date, bringing it forward some months so the percentage completed jumps up accordingly. Who knows what percentage of the actual work has been completed between updates because we don’t measure that metric apparently.

What is more pertinent to the question that we should all be wanting an answer to (Will it hold water?) was Mr Bedrock-everywhere Scott’s comments around the grouting. Of course, most of the Councillors had no concerns at all in this regard, and were busy patting themselves and others on the back for doing such a great job to get this far.

Will all this work be in vain?

In answer to Councillor Walker’s question Mr Scott explains that the grout curtain seals substrata and stops leakage under the dam. It is a process where we drill 44 meters down into the substrata and pump concrete into the holes sealing up all the leaks. We budgeted for 5000 meters of drilling and now have completed 17000 meters of drilling which is much more than originally budgeted.

When Councillor Walker asked for clarification that they are drilling down to bedrock Mr Scott replied “No.” When then asked how far they drill he responds.”it is through the rock, all rock has permeability. The deeper you go down the longer the path so there is less flow so the grout curtain is deepest at the deepest part of the reservoir and it is through rock sealing up .. sealing .. or reducing the permeability of the rock.”

Councillor Greening followed up Councillor Walker’s questions with “In the past when you have spoken about grouting you have explained it in terms of drilling down to bedrock. Have we drilled down to bedrock given that was best practice or have we not drilled to bedrock and stopped at 44 meters?”

Mr Scott responded “Drilled through bedrock The dam is built on rock, we have cleared the overburden and got down to sufficiently strong bedrock to found the dam, drilled down through the bedr… through the rock up to 44 meters deep to reduce the permeability of that rock.”

Again, Councillor Greening sought clarification “we have got grout holes drilled down to bedrock and through bedrock is what you are saying?”)” And got the response “Through the rock that is right.”

One more attempt from Councillor Greening for a direct answer “through bedrock? draws yet another blank with Scott’s “yeah through yeah through founding rock” answer.

So what did we learn from that exchange? We learned that their initial site investigative work suggested that they would need to drill 5000 meters of grout holes. Once they started they decided that they needed to drill 17000 meters (up to 44 meters deep) of grouting. What we weren’t told is whether they believe they have now sealed the reservoir or whether they stopped due to budget or other constraints (such as still no sign of solid rock at 44 meters).

Mr Scott’s dancing around the answer of are they in solid bedrock with yes bedrock/rock/all rock is permeable/founding rock could be a confirmation of the word on the street that some of the holes were seemingly bottomless soft rock/clay. Possibly the result of building a dam on a fault line – sorry, according to Mr Kirby Council Head Engineer it is just a convergence of “shear zones” running through the dam site.

The stumbling Mr Scott did around the grouting “sealing up .. sealing … or reducing the permeability” also suggest that he was reluctant to say that the grouting to date was a success at sealing the reservoir floor, or sealing it sufficiently that we have a dam and not a bridge.

One thing is very clear, and that is that the initial dam site examination was woefully inadequate. If we examine Mr Scott’s comments in light of studies about dams we find that not only was the site selection particularly bad, but the investigation into the site was woeful, and now there questions over the construction process. But don’t take my word for it, lets have a look at some instances.

Our findings show that bedrock permeability is a higher-order control on flow path distribution across catchment scales, and hence on MTT scaling relationships. This is particularly significant as more and more researchers are finding that bedrock groundwater makes significant contributions to streamflow in catchments where the bedrock was previously thought to be impermeable [Gabrielli et al., 2012].
Source

This extract highlights that even “bedrock” can be more permeable than first thought, agreeing with Scott’s assertion that all rock is permeable. However, as he was reluctant to be committed to the term “bedrock” we are left questioning what kind of rock the dam is built on and where exactly it sits on the scale of permeability.

There are two main types of porosity: intergranular porosity that characterizes sands, gravels and mud, and fracture porosity in hard rock. Fracture porosity forms during brittle failure of hard rock or cooling of lava flows. Fracture networks that are connected can provide pathways for fluid flow even when the host rock is impervious (e.g. granite, basalt, indurated sandstone). Highly productive aquifers are not uncommon in fractured bedrock.
Source

Here we discover that “highly productive aquifers are not uncommon in fractured bedrock.” One would be “very surprised” to learn that there are highly productive aquifers under a dam site located between to major fault lines and sitting on yet another convergence of sheer zones! Doesn’t sound like a place you find fractured bedrock at best to me.

Fracturing of the rock commonly accompanies faulting, and a fault may be marked by a zone of fracturing rather than by a single fracture. Faults and the fracturing that accompanies them also afford avenues by which surface weathering and solution activity can attack the rock. Fault zones present a possible escape route for the reservoir water, and faults also indicate, in varying degree, the hazard of continued or repeated movement.Faults in the foundation and abutment rocks at a dam site and in a reservoir area introduce problems of bearing strength, stability, and water-tightness and, therefore, sites that contain them should be avoided. Stable dams can be designed for faulted foundations, but the cost of the necessary remedial treatment may be prohibitive.
Source

“Sites that should be avoided” if this was a dictionary entry I would suggest that the Waimea Irrigation Dam site would be the explanation following it. Not only can we expect a leaky reservoir, we can expect that there is likely to be further movements adding to our woes for years to come (should the dam be completed) and of course the remedial work might be prohibitive were it not for the fact that there is no off-ramp for this council. We must have the Kempthorne/King/Bryant/Mailing memorial no matter what.

Conclusions Monitoring of seismic activity
• Prior to construction,
• During impounding of reservoir, and
• During first years of reservoir operation is highly recommended for (i) large storage dams, and (ii) dams located in tectonically stressed regions.
Source

I found this comment particularly chilling. I don’t think there is any dispute that we have a dam located in a tectonically stressed region (in fact I would suggest we are right on top of a fault line), so have we been monitoring seismic activity at the dam site before, during, and looking ahead into the future?
As the article goes on to explain below, the pressure exerted by the reservoir water has the potential to create seismic events, especially in a site already loaded with shear zones and weak rock. This is important because any failure of the grout curtain, assuming it works in the first instance, could well see a failure of the dam by way of erosion of the foundation. I mean what are the chances of an earthquake cracking an unreinforced concrete grout curtain places on a fault line?

The statistics of dam failures performed by ICOLD [8] takes into account dams 15 m high or more or with a storage volume of at least 1 million of cubic metres. The results of this work can be summarized as follows (data from China and the URSS were not considered): the most common type of failure in earth and rockfill dams is overtopping (31% as a primary cause, 18% as a secondary cause), followed by internal erosion of the body (15% as a primary cause, 13% as a secondary cause), and in the foundation (12% as a primary cause, 5% as a secondary cause) ,,,
Failures leading to catastrophic consequences occur typically at first filling and full reservoir stage, although overtopping during construction has caused, in some cases (for example Panshet dam in India, Sempor dam in Indonesia and S. Tomas dam in Philippines), several victims.

A dam [38] radically alters the natural antecedent state of stress in the valley flanks and river channel; it adds weight, a more or less concentrated vertical load resulting in a complex compression and shear forces in the foundation. It transmits forces caused by loading during its operational life (water load, temperature effects, etc.). These forces produce compression, shear and often upstream tensile stresses. Water seeps into pores and rock discontinuities of the foundation; seepage forces can be considerably high and act in extremely unfavourable direction for stability of dams. The main steps of stability analysis of such a complex structure made up of rock mass and concrete structure consists of the definition of the possible modes of failure and calculation of the equilibrium conditions for stability. Geological and rock mechanical studies are required to evaluate the possible modes of failure and the variables of the problems. Analytical or numerical methods are used to assess dam foundation stability conditions.
4.1 Geological and rock mechanics studies
Geological studies with field explorations help to determine the feasibility of a dam and decide the general layout of the works including dam type and position. The first geological work [38] is to outline the regional and thereby the site structure, then the genesis and history of rocks and hence their stratigraphic, petrographic and tectonic descriptions which indicate the type of the problem to be expected. High-scale hydrographic and hydrogeological studies are required since a dam construction determines the presence of a new water reservoir which changes the original superficial and underground water flow. The principal purpose of rock mechanics studies is the characterization of the rock mass hosting the dam in order to assess deformation and strength features and to evaluate the geometrical and physical properties of singular and systematic rock discontinuities.