Methods and data quality at Seepegel

Level and discharge values come from the hydrological services named at each station. Weather information may be station measurements or model and forecast data; its source is therefore part of the value. Scientific lake temperature models are not sensor measurements either. The sources page names the operator, original address and, where available, the licence.

Measurements are taken over unchanged in their technical meaning. Seepegel unifies the display of date and time and formats units for the chosen language. No missing live values are invented and no stations are merged into an artificial series.

Updating depends on the original source and typically lies, per station, between roughly 10 and 60 minutes. Retrieval, processing and publication can add further minutes. What matters is therefore always the measurement time shown with the value, not the time of the page visit.

If a source is missing, the last available value may remain visible with its original timestamp. Missing values are not zero: they prove neither a dry channel nor an unchanged situation. Even an available value may be provisional: the FOEN distinguishes raw, checked and validated data. Operators may correct them. Seepegel's display does not replace this expert validation.

Changes over 24 hours or seven days are derived from values of the same station and unit. Without a comparison reading at a suitable time, an exact change is not established. For seasonal levels, Seepegel uses daily statistics provided by the FOEN. The period is often 1991–2020; the one stated on the chart applies. The current level is compared with historical daily means for the same calendar day.

The minima and maxima of that reference concern its period and daily means. They are neither all-time records nor instantaneous extremes. Our temperature and weather comparisons may use different periods and should not implicitly be equated with this FOEN reference period.

The station comparison uses the last 30 completed UTC calendar days, excluding the current day. Stored readings of the same station are averaged for each day. In Switzerland, UTC day boundaries fall one or two hours after midnight depending on winter or summer time. At least 7 daily means are required; the displayed count shows how many days actually contribute.

Each available day counts once, even if it has gaps. Missing days are not filled in. Minimum, median and maximum come from those daily means, while the current value being compared may be a single reading. A brief peak can therefore exceed every daily mean without being a record or an official warning threshold.

For the rank, lower daily means count fully and equal ones count half. If all reference values and the current value are identical, the result is 50 per cent. This short-term statistical comparison is neither a return period nor the probability of flooding next year.

Alplakes lake temperatures are based on Eawag's physical Simstrat model, which describes the lake's vertical temperature distribution. A modelled near-surface value is not a measurement at a particular swimming beach; depth, proximity to shore and local inflows can produce different temperatures there. A station on a tributary describes that river reach, not automatically the lake water.

For its annual comparison, Seepegel uses daily means from the stored Alplakes model series. The current year is excluded from the reference. At least 5 completed years with values for the same calendar day are required; 29 February is omitted. The displayed range names the available reference years, without guaranteeing a gap-free series. This calculation does not turn model history into decades of sensor measurements.

The water-balance pages compare measured inflows and outflows. Not every small confluence has a station; precipitation on the lake surface, evaporation, groundwater, withdrawals and storage change are partly missing. The visible difference is a partial balance of the monitored stations. On its own, it does not prove an increase or decrease in the lake's stored volume.

Map lines also show the geographic course of a water body, not the spread of a current flood wave. Seepegel supports understanding and comparison. For safety decisions, only official warnings and local instructions apply.

Every detail page names the station, measurement time and source, so a value can be checked against the original. Source operators can correct historical data afterwards; an already displayed trend can therefore change. We receive reports of incorrect assignments or units via the contact address in the imprint.