F-0041 Copies of emails in which one point alone falls out of the dredging estimate

(Said to be a copy of email records. Parts of the senders, recipients, and dates are withheld.)

From: Survey & Design S
To: Hakozaki Reservoir Management Office
Subject: Delivery of bathymetric survey deliverables (Hakozaki Reservoir sediment survey)
Date: October ◯, 2025, 10:◯◯

Thank you as always for your business. Please find enclosed the full deliverables for the above-referenced work. Sedimentation has advanced across the whole pond, averaging about 0.4m shallower against the design bed level. Please see the sediment volume calculations for details.

One supplementary note. At one point on survey line No. 3, a depth value of 41.2m was recorded. As it is not continuous with the surrounding values, we judged it to be noise from multipath reflection or the like, and have excluded it from the deliverables. We ask for your understanding.

Best regards.

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From: Management Office T
To: Survey & Design S
Subject: Re: Delivery of bathymetric survey deliverables (Hakozaki Reservoir sediment survey)
Date: October ◯, 2025, 16:◯◯

Thank you. The deliverables have been received.

About the point you excluded as noise: checking against the location map, it appears to fall near what the old observations called the third sounding point. The old logbook also notes that there are months with no figure recorded for this spot. If it is no trouble, could we have the raw data from before the exclusion, for reference?

All we have here is the old bound volume; no one remains who knows the circumstances of that time.

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From: Survey & Design S
To: Management Office T
Subject: Re: Re: Delivery of bathymetric survey deliverables (Hakozaki Reservoir sediment survey)
Date: November ◯, 2025, 18:◯◯

Sending the raw data (attached). Also, as it caught our attention, we re-measured the point in question alone on November ◯. The result was 4.6m, continuous with the surroundings, and nothing abnormal. The October value did not reproduce.

For internal confirmation we also measured once more on a different day with different equipment; that run returned a value of 52.8m. Why the two runs do not agree is under investigation. By the inspection records, both instruments are normal.

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From: Management Office T
To: Survey & Design S
Subject: Handling of the point in question in the dredging working design
Date: January ◯, 2026, 9:◯◯

Thank you as always. As we organize toward the working design for the dredging, we would like to consult you about the handling of the point in question.

The dredging quantities are built on the premise of removing the accumulated silt and returning the pond to its design depth. The point in question is currently deeper than the design depth, so on that premise the quantities cannot be drawn up. Returning it to the design depth would mean a filling work, and an order to fill in the pond cannot be placed. Would it be possible to arrange for the point to be left out of the work area?

We plan to place the order within the fiscal year. We are sorry for the trouble, and thank you for your consideration.

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From: Survey & Design S
To: Management Office T
Subject: Re: Handling of the point in question in the dredging working design
Date: February ◯, 2026, 20:◯◯

Attached is a revised work-area plan. The point on line No. 3 has been left out of the work area as a set-aside section, 20m around. The quantity calculations have been replaced as well.

Also, a report we are late in making: at the site confirmation on January ◯, I went out on the boat myself and took a sounding with a rope and weight. The weight touched bottom at 4.7m, and the feel of the touch was ordinary. But while the weight sat on the bottom, the echo sounder on board kept returning values in the 38m range at the same point. At the same time, at the same point. Which number to doubt, we are in no position to judge. As the point is a set-aside section, neither value is included in the deliverables.

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From: Survey & Design S
To: Management Office T
Subject: Regarding survey work going forward
Date: April ◯, 2026, 17:◯◯

Thank you as always. Regarding the above: as for the surveys during and after the dredging work, we must ask, with apologies, that our involvement end with the scope covered so far. As for the reason, please let us leave it at internal arrangements.

One thing to add about the raw data. What we sent is all of it. The rest, we found at the internal confirmation stage, had not been saved. The reason is not known.

Thank you for the long association.