A portable water-stage recorder

Transcription

1 A portable water-stage recorder for experimental hydrological measurements Jaroslav Martinec Federal Institute for Snow and Avalanche Research, Weissfluhjoch, Switzerland; Hydraulic Research Institute, Prague, Czechoslovakia Abstract. Hydrological studies must often be carried out at sites where accurate recording of water-level fluctuations cannot be ensured by the permanent network of water-gauging stations. A light, portable water-stage recorder was used to synchronize experimental measurements of hydraulic parameters pn representative river reaches for research on flow conditions in artificial reservoirs and for investigations of glacier run-off in remote areas. LIMNIGRAPHE PORTATIF POUR MESURES HYDROLOGIQUES EXPERIMENTALES Résumé. I1 est souvent nécessaire de faire des études hydrologiques dans les endroits où les fluctuations de la surface d'eau ne peuvent pas être enregistrées par le réseau permanent des stations limnigraphiques. Un limnigraphe portatif léger a ét6 utilisé pour synchroniser les mesures expérimentales des paramètres hydrauliques dans les sections représentatives des rivières, pour Btudier les conditions de I'kcoulement dans les réservoirs artificiels et pour examiner le débit glaciaire dans les régions peu accessibles. REGISTRADOR PORTÁTIL DE NIVELES PARA HIDROLOGiA EXPERIMENTAL Resumen. Con frequencia es necesario realizar estudios hidrolbgicos en lugares en los que las fluctuaciones de nivel de agua no se pueden registrar por la red permanente de estaciones limnigrbficas. Se ha utilizado un registrador portátil de nivel de agua para sincronizar las medidas experimentales de los parámetros hidráulicos en secciones representativas, a fin de estudiar las condiciones de flujo en los embalses y examinar la escorrentia glaciar en áreas remotas. INTRODUCTION The water stage and its fluctuations must be taken into account in every hydrological measurement on rivers. Routine hydrometry is carried out at permanent watergauging stations with water-stage recorders. In addition, and especially where the hydrometric cross-section must be moved to some distance for practical reasons, 41

2 J. Murtinec readings on an auxiliary staff gauge are taken at regular intervals. This practice has been found inadequate for special hydrological studies. Some time ago, a simple portable light-weight water-stage recorder was developed by Javorsky (Hydraulic Research Institute, Prague) in co-operation with Fric. Some recent examples of its application can now be given. DESCRIPTION OF THE INSTRUMENT The general appearance of the recorder is shown in Fig. 1. Fluctuations of the water level are followed by a float, which is attached to the lower end of a rod. The float is placed in a perforated cylinder, which is submerged in water. The stilling effect of the cylinder can be adjusted to the respective flow conditions by changing the size of the openings. A pen is attached to the rod, and the water stage is recorded on a revolving drum actuated by a clock. The speed of rotation can be adjusted either to one revolution in 12 hours or one revolution in 6 hours. The rotating drum is protected by a cylindrical cover. The whole equipment is supported by another rod, which is driven into the river bed when the recorder is temporarily installed. All the components pack into a bag which can be carried by one person. Figure 1. The portable wuter-stage recorder near the outflow from the Scaletta Glacier in the Swiss Alps. 42

3 A portable water-stage recorder for experimental hydrological measurements EXAMPLES OF APPLICATION Studies of run-off in rivers with regard to a possible loss of water due to geological faults [ref. 11 comprised for some time the broadest field of application. In such measurements, a number of portable water-stage recorders are installed at selected intervals along the river, sometimes over a large distance. Water stages are then simultaneously recorded and the discharge evaluated at the respective cross-sections. A decrease of discharge in the downstream direction indicates a loss of water from the river channel. In studies of flow conditions in backwater reaches, recorders can be installed temporarily along an artificial reservoir formed by a dam. Fig. 2 shows records of water level at different localities on the Slapy reservoir in Czechoslovakia, where periodical standing waves caused by the operation of turbines could also be studied [2]. In studies of velocity losses in rivers due to roughness and channel irregularities [3], it is necessary to measure discharge, sediments, slope and a number of cross-sections, which may take more than one day. Discharge must be expected to change in the meantime, making comparison of the measured values difficult. By using the portable water-stage recorder, it is only necessary to note the exact time of each measurement in order to relate all data, e.g., the cross-sectional areas or water levels of the longitudinal profile, to a reference level for which the discharge is evaluated. An example of this procedure is shown in Fig. 3. If such measurements are Figure 2. Fluctuations of water level at different localities along the Slapy reservoir in Czechoslovakia. 43

4 J. Martinec ZU H A hrs 16 E u $ 15 ((I +.' In & w s io Figure 3. Water-level recording during the experimental measurement of hydraulic parameters on the river Jizera hrs Figure 4. Comparison of hydrographs of a glacier-fed stream. 44

5 A portable water-stage recorder for experimental hydrological measurements repeated at various water stages, the reference level can be related to a fixed elevation point by levelling. In some cases, as for example in glacier run-off studies, measurements are carried out in remote areas, where a temporary installation of a regular water-stage recorder would be too expensive and time-consuming. This situation is illustrated by Fig. 1. A comparison of hydrographs along a glacier-fed stream is shown in Fig. 4. The first hydrograph in the vicinity of the glacier was recorded by the portable water-stage recorder, which was installed for 24 hours at an altitude of 2,380m. Further downstream heavier equipment was installed for several months (hydrograph No. 2). The last hydrograph (No. 3) was recorded by a regular water-stage recorder of the permanent hydrological network. CONCLUSION The fluctuating character of water level in small streams, rivers, natural and artificial lakes has to be taken into account, especially in experimental measurements which necessitate high accuracy over a long period. Several examples have illustrated that a light portable water-stage recorder can be of assistance in such cases. BIBLIOGRAPHY / BIBLIOGRAPHIE 1. SlepiEka, F Vodnost toku a hydrogeologická stavba Území [Runoff in rivers and hydrogeological structure of a region]. Proceedings 3. Hydrometeorological Conference of 1954, Prague, p Martinec, J.; Urban, J Flow conditions above a high dam. Proceedings IAHR XIth Convention, Dubrovnik Martinec, J Rychlostní ztráty v nepravideln9ch %c%ch tratich [Velocity,losses in irregular channels]. (In Czech with English and Russian abstract.) Práce a studie VUV Praha, vol