So, I let be persuaded, despite I know, that it will not be O.K., and a supplementary programme has to be found.

Anyway, how to find a moment, when the river navigation could be optimal, in order to slide smoothly? We do not wish to overcome flooding, in order to run away the bank and rescue our lives.

At present, at quick information run era, there is no problem to surf suitable web-site internet pages, for instance various administrations of river-basins or meteorologic institute and find the right page informing about a stage or flow in certain place on river chosen. In kilometrage or in other special waterman literature, or from friends, we can find the respective recommandation where we can go. However, everything has its exceptions.

We can assume, provided there is sufficent water-level on river-flow, that this stage persists. On the other hand, we know now that it will last for couple of days. Let´s take an example: lower Sázava: there is dry weather in summer, on Friday rains in Žďár nad Sázavou, so, we cannot assume that the rapids in Krhanice will be passable. Water-speed, which flows 3 kms/hour, sometimes more, sometimes less, depends on many aspects (on banks´ character, on terrain slope, on obstacles in river-bed, on base-feeding with water and many others).

Anyway, watermen are always interested for small rivers - with its small river-basin – these rivers have, however, seldom sufficient water-stand. How to estimate it? Frankly speaking, it is not easy. You need to follow-within long time period - the situation in an area, precipitations, flowings off, to risk it sometimes and try to go to the brook chosen. After certain period, we receive an experience and  prove (demonstrate) - with relatively great probability- to estimate suitable water stage. A typical example is (if we do not live at  river banks) Smědá-river. Flowing off conditions changed a lot from a moment when the forests of Jizerské Mountains „disappeared“. There is available enough water there for couple of hours only - in case of its ideal stage - heavy rains for several hours, rain into snow-thaw, that ´s all. However, sunshine and snow do not deliver sufficient water-quantity for Upper Smědá.

If in certain area prevails heavy rain for longer time-period (before it was quite dry there), and we wish to start on Saturday morning, and it stops raining on Thursday morning, so it is no guarantee that  water-stand will be sufficient. Again, the information received of longer time-period, from a place where we intend to paddle, could be taken into consideration.

Shortly, we wish to express it as follows:

High probability of water sufficiency for navigation:

- heavy rain within longer time-period, rain into snow.

- in general, humidity stage in region (snow, rain), the base is filled.

- lower flow slope.

- bigger river-basin.

- suitable base for water-capture (peats, sands, etc.).

- banks´ overgrown and overgrown in general (forests hold water for longer time-period, so they settle outlets).

- higher temperature (in case of outlets of snow and glaciers).

Attention: sands and limestone have its specific character. In these areas, the water carries out (proves) to load for longer time-period, successively it flows away for longer time. Flowing through is more levelled, the curves are not so steep. Let´s take notice of Hřenská Kamenice-river or limestone-rivers in Dinar System, the floodings are exceptionally here, and sufficient water-stand remains for longer time.

Well, now we are able to estimate, if and when we can pass the suitable flow. Anyway, one notice more: each flow has its river-basin. We assumed in past, that only the flows with river-basin up to 100 km² and more could be passable (In our countryside, we mention). Of course, the rivers are navigable from its source, in case of strong karst spring. Anyway, we can see at present, that the flows with lower river-bed are passable exceptionally - you need well and  seriously follow and watch water - level!

How to do it, comparing various water index-registers? This information could be perfidious. According to experience of  past years, you have to take into consideration a fact that the river changed or could change after flooding, even also in its water-profile, and it is not good. If, for instance, the water-index register was settled in a place where river-bed was wide 20 m and deep 0,5 m, after inundation is twice so big and deep (provided  index register lath was saved), so the registration (moreover, on washed out place) will not be for flow-passage decisive. Anyway, these things are mostly removed very quickly, we have to take in mind that the changes occur. Watermen would follow data and  inform each other accordingly. Water index register points are mostly placed in sections where the river has a minimal chance for change (under standard conditions) - i.e. at levelled stages, behind bridge-pillars, etc.

Further perfidious data: if we are in a hurry to pass a river immediately with ice-departures, could be these ice-appearances. If on water index-register point the river is frozen, and the ice-barrier starts to form, so even a small water-level arise causes „apparent passage“. Water index-register shows necessary 150 cm (example), this is a flow of 20 cubic meters, but, in fact, the water does not move at all, it is swelled up ice, and flow makes 2 cubic meters only. The flow is deducted back according to the stand. Originally, the flow is measured by means of flow-measure and an indication on water-register lath (limnigraf or other scale or other measure instrument) is added to it. This is worked by curve and obtained stage is deducted only, and it is taken as fix that the flow corresponds to this curve. However, it happens that definitive changes could occure. All these measures and calculations are made periodically, but not each year.

So, if we meet with a flow 60 cubic meters on Ohře-river in Loket, and we do not have any idea that somewhere in Ore Mountains it could fall heavy rains, so, we could assume (we read it easily from a map or kilometrage) that some manipulations on water-works along upper flow were effected. So, the next day could be dry again. Obviously, it was extraordinary manipulation.

Anyway, let´s return back to weather, especially to spring one. Short information, with regard to this year´s situation, is available, as follows:

- if it rains into snow, the water will increase.

- if there is heavy rain upstairs in mountains, we can assume quick swelling up of water-level also in lower flows.

- with arising temperature, water flows first from snow on lower flows, successively in middle section, later from moutains, situated upstairs.

- in areas, where the forests are missing, the water will arise quicker, and quicker falls.

- sun alone cannot cause flooding from snow-covering, but there is mostly sufficient water-level for navigation (provided the temperature is not extremely, of course).

- the countryside with forests keeps water a little longer, the same make peats.

- first snow-thaw and hard snow-thaw makes a difference, from last rests of high situated places, do not flow much water.

So, this experience could be presented more. Anyway, everybody who wishes to pass the river, has to follow the weather forecast and its development, you have to achieve and watch bank of your river and start when the conditions are favourable enough.

Interesting references:

www.chmi.cz

www.povodi.cz

www.raft.cz

www.kanoe.cz

etc.

Text: Vojta Jančar

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