Ice in the Environment: Proceedings of the 16th IAHR International Symposium on Ice Dunedin, New Zealand, 2nd–6th December 2002 International Association of Hydraulic Engineering and Research

USE OF DIGITAL TIME LAPSE VIDEO TO MONITOR RIVER ICE - PRELIMINARY REPORT

Hans-Petter Fjeldstad1, Oddbjørn Bruland1 and Knut Alfredsen2

ABSTRACT In order to predict effects of expected climatic change on fish in rivers we need better knowledge about ice. In this project the conditions and processes creating frazil ice and anchor ice will be extensively studied through observations and a modeling program. Two study sites are chosen in the River Orkla, Mid-Norway. Digital time lapse video recording is used to detect both surface ice, frazil ice and hopefully anchor ice at a suitable spot in the river. Discharge and temperature recordings with high accuracy and climatic observations at the riverbank together with the video will monitor the conditions at which the ice creation processes start and evolve. To assess causes of climatic change on ice processes and fish habitat we will use calculated climatic data from the Norwegian RegClim project. These will be used to generate predicted discharge and temperature time series for the study sites. The instrumentation was tested during the spring 2002 and some experiences and preliminary results are presented in this paper. INTRODUCTION Supercooling of water is a function of the rate of which the flow can transport heat to the surface (Carstens, 1966) and therefore ice production depend on local flow conditions. In supercooled water frazil has capacity to adhere to other objects in the river, such as rocks and constructions. As a result frazil creates vast problems in certain rivers (Matoušek, 1992). Surface ice, frazil ice and anchor ice in rivers cause severe changes in the fish habitat, but how this influence the behavior, survival and reproduction of the fish has so far not been extensively studied. Several models for simulating creation of ice in rivers have been made over the years e.g. RICE© and DynaRICE©. These are mainly adapted to slow running rivers and the performance in steep Norwegian rivers is therefore occasionally poor (Bjerke, P.L., personal communication). Norwegian scientists have made prognoses for climatic changes as a consequence of

1 SINTEF Energy Research, 7465 Trondheim, Norway. Email: oddbjorn.bruland@sintef.no, hans-

petter.fjeldstad@sintef.no 2 Dept. of Hydraulic and Environmental Engineering, NTNU, Trondheim, Norway. Email:

knut.alfredsen@bygg.ntnu.no

global warming (Benestad, 2001). Modelled warming rates for western Norway are 0.2–0.3 °C per decade the coming 50 years as a result of this (Hanssen-Bauer et.al., 2000). Prognoses of climatic change in Norway indicate dynamic changes and increased cyclonic activity, which leads to western winds, often at high air temperatures in wintertime. In the Norwegian lowland this generate temperatures above freezing resulting in melting processes and ice break up. Analysis of climatic prediction will therefore be the foundation for estimates of the frequency of such episodes and the estimates can give information of the effect of the episodes in the future. Climatic changes will vary between different climatic regions but will in any case have influence on Norwegian rivers and the organisms living in them (Jensen 1992). It is therefore important to obtain better knowledge about the consequences of the climatic changes on ice in rivers as a tool for the management of the rivers in general and for operation of hydro power plants in particular. Warmer winters will result in more frequent ice break ups. Such episodes are described as bottlenecks for parts of the aquatic life including Atlantic salmon and brown trout (Cunjak et al., 1998). A different ice regime will change the temperature and light conditions and ice formation in the rivers may change the distribution of physical habitat (Tesaker, 2000). There is a relation between the available physical habitat and how it is utilized by the fish. This relation can be shown by studying the fish preferences (Bovee, 1982). The fish change behaviour corresponding to water temperature and thereby change its preferred habitat (Heggenes et al., 1993, Heggenes and Fjeldstad, 1999). Habitat computer modelling on summer conditions has already been carried out for a couple of decades and ongoing studies use knowledge on winter habitat to extend the modelling to winter conditions (Alfredsen and Tesaker, 2002). As anchor ice and stationary and moving formations of ice affect the available physical habitat it is likely to believe that ice and snow prevent fish from selecting optimal physical condition and that ice force fish to migrate on a shorter or longer distance (Whalen at al., 1999). METHODS Study sites We have chosen two sites of different characteristics in River Orkla, about 80 km south west of Trondheim in Mid-Norway. The watershed of Orkla is 3052 km2 and covers an area from the sea and up to the mountains, some of them reaching 1600 meters above sea level. The climate in the region is sub arctic with moist summers and severe winters. Mean annual runoff for the catchment is 22 l s-1 km-1 (70 m3 s-1) The water regime is heavily regulated by 5 hydro power plants and several large reservoirs, all constructed in the period from 1978 to 1985. This has given smaller spring floods and summer discharge, while winter discharge has increased. The river used to be permanently ice covered in winter, but the increased winter discharge from high head power plants has created a more dynamic ice regime on the different parts of the river. Both study sites are situated in the lower part of the river, some 35 and 60 km from the sea respectively and with altitudes of 130 and 200 meters above sea level. The lowermost site, site 1, is located at Meldal, between the outlets of the two lowermost power plants, some 20 km downstreams from the outlet of Grana power plant. Site 2 is situated at Merk, a few kilometers upstream from the outlet of Grana power plant. Site 2 is influenced by the Brattset power plant further upstream. Atlantic salmon can run 92 km up the river while brown trout is found in rivers and lakes in most of the catchment.

The study sites were chosen to represent typical ice affected reaches where Atlantic salmon and brown trout is present. So far in this project data have only been collected from site 1. Site 2 is not mentioned later in this paper.

Figure 1: Study site 1 at Meldal in River Orkla Field Observations In order to understand ice processes it is important to have temperature data in water and air as well as discharge data. Water temperature is collected with a Vemco 8 bit Minilog. Discharge and air temperature data is obtained from the power company from the locality of Bjørset dam, a few kilometres downstream from site 1. Observation of ice is done automatically by a time lapse camera system. The system consists of a JVC GR-DV J70EG digital video camera with a controller that grabs a short video sequence at programmed intervals. So far the video data has been stored locally with the camera. This is a weak point, which we experienced when the battery ran out of power without our possibility to monitor it online. The coming winter a modem link will be connected from the camera controller in order to transfer data directly to our office. It is important to remember that observations of ice conditions as a function of water regime and temperatures is strongly connected to the specific locality, which means that a given air and water temperature at one river reach does not give the same ice production as at another reach. We have used a Leica 307 total station to do an accurate mapping of the bathymetry at site 1. The site is about 100 metres long and we have collected around 700 geometrical points to represent the riverbed. A Nortek acoustic Doppler profiler, ADP, is used to collect water velocities. The ADP is mounted under a surfboard that is dragged over the river while it measures the velocities in 10 cm intervals vertically. The position of the surfboard is measured with the total station in order to localise each velocity measurement. With this method we are able to obtain an accurate map of the hydraulic conditions and the spatial variation at different discharges.

Map of Norway

Site 1

Orkla River

Figure 2: Water velocity measurements with ADP surfboard Data analysis Video images are grabbed by using standard frame grabbing software. Images are analysed using the Matlab Image Processing toolbox (Mathworks, 2001). Areas of the picture that are not part of the river surface are masked to prevent them from beeing included in the calculation and a filter is applied to extract all ice “pixels” in the image. The threshold between ice and water is at the moment set from a manual inspection of the image and further field verification is necessary. The filtered image is then analysed to find the proportion between ice and open water. The algorithm is currently set up for floating ice, but work is underway to try to distinguish other ice forms from the picture. Work is also needed to clean up reflections in the water and droplets on the lens that interferes with the automatic process. At the moment these tasks are done manually.

Figure 3: Ice and snow in Orkla at Site 1 in Meldal seen through the video lens

Figure 4: Picture from figure 2 masked (to the left) and then filtered (to the right) When video pictures have been analysed we can connect them to temperature and discharge data. This will tell us which physical conditions that give ice production of different kind. It will also be possibilities to look at ice cover and ice break ups as a function of weather. ICE OBSERVATIONS AT MELDAL The first 15 days of March 2002 the water temperature varied between –0.05 °C, and +1.03 °C. Air temperature was measured every hour and was between –12.4 °C and +5.4 °C in the same period

Figure 5: Air and water temperature at Site 1 in the period 1st – 15th of March It is worth noting that the air temperature at this time of the year vary extensively over the day. The warmest hour of the day in the 15 days period was hour 15 (3 pm). Only

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one day in the period had temperature below freezing in hour 15, while the coldest hour, hour 5 (5 am) had air temperature between –11.7 °C and +0.5 °C, with only one day above the freezing point in this hour. We have grabbed ice observations on video for only three days in this period. By analysing the pictures we were able to calculate the percentage of ice on the water surface as a function of total surface area. One example of this is the 7th of March when the amount of ice was at the highest early in the morning and was reduced to almost zero in the afternoon. The same day the temperature observations show super cooled water the whole day. The air temperature was under –10 °C in the morning and rose to around zero at noon and stayed at this level the rest of the day. The two other days in the period there was hardly any ice observed on the surface.

Figure 6: Ice amount analysis done for the 7th of March 2002 We have also video pictures from a period later in the spring, mainly from the month of May. Not surprisingly there is very little ice observed on these pictures and there is a question if the ice on the surface in this period is melting ice and snow from higher altitudes of the river. Manual analyses of the video pictures indicate that most of the ice we observed in March 2002 is frazil that has frozen into larger ice floes, or broken floes that has been transported downstream. DISCUSSION AND FURTHER WORK Our project started late last winter and due to technical challenges and a fast coming spring we were not able to collect enough relevant video data to create time series that can help us to understand the ice processes as a matter of climate in River Orkla. We have in the preliminary studies seen that we are able survey the river ice situation by use of video techniques but so far we have only developed the techniques and tested the equipment in order to understand the ice regime at the specific study sites. We have been able to detected surface ice on the video sequences but have so far not been able to explain the ice origin. Existing experience show that weather episodes with heavy rain and temperature above freezing result in violent ice break ups during winter, and such episodes are expected to be more frequent in a changing climate. Break ups are often difficult to observe because the episode is over before one is able to get out in the field. Design of a monitoring system with sensors or other technical equipment is a great challenge as a consequence of the violent nature of an ice break up. As ice in general and such episodes in particular affect fish habitat it will be a new angle of attack to use

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online video monitoring as an effective tool to achieve better knowledge about winter habitat. The studies in this project started in the end of last winter and will last for another four winter seasons. The months of November throughout May represent the season influenced by ice on our study sites, with the period from November to March as the most interesting for ice production. We therefore expect that we will be able to collect enough field observations to understand the ice processes on the study sites and their influence on fish habitat in the coming years. The analyses of video pictures must be automatised to a larger extent in order to obtain more information and the analyses must be expanded so that different types of river ice can be identified. This work is going on and the coming winter will be the first season with a full observation programme and subsequent analyses. ACKNOWLEDGEMENT The authors wish to thank the power company in Orkla (KVO) for data support. The Norwegian Energy Directorate support this project. REFERENCES Alfredsen. K. and Tesaker, E. Winter habitat assessment strategies and incorporation

of winter habitat in the Norwegian habitat assessment tools. Hydrological Processes 16(4): 927–936 (2002)

Benestad, R.E. The cause of warming over Norway in the ECHAM/OPYC3 GHG integration. International Journal of Climatology 21: 371–387 (2001).

Bovee, K.D. A Guide to Stream Habitat Analysis Using the Instream Flow Incremental Methodology. Fort Collins, Colorado, National Biological Service (1982).

Carstens, T. Experiments with supercooling and ice formation in flowing waters. Geophysica Norwegica XXVI(9) (1966).

Cunjak, R., Prowse, T.D. and Parrish, D.L. Atlantic salmon (salmo salar) in winter: "the season of parr discontent? Canadian Journal of Fisheries and Aquatic Sciences 55: 161–180 (1998).

Hanssen-Bauer, I., Tveito, O.E. and Førland, E.J. Temperature Scenarios for Norway. Empirical Downscaling from the ECHHAM4/OPYC3 GSDIO integration. The Norwegian Meteorological Institute. Report 24/00 (2000).

Hanssen-Bauer, I., Tveito, O.E. and Førland, E.J. Precipitation Scenarios for Norway. Empirical Downscaling from the ECHHAM4/OPYC3 GSDIO integration. The Norwegian Meteorological Institute. Report 10/01 (2001).

Heggenes, J., Krog, O.M.W., Lindås, O.R., Dokk, J.G. and Bremnes, T. Homeostatic behaviour responses in a changing environment: brown trout (Salmo Trutta) becomes nocturnal during winter. Journal of Animal Ecology 62: 295–308 (1993).

Heggenes, J. and Fjeldstad, H.-P. Habitatvalg til laksunger og ørret i Stjørdalselva ved Gudå, Nord-Trøndelag, og modellerte konsekvenser av varierende vannføring ved lav vanntemperatur. [Habitat selection of juvenile Atlantic salmon and brown trout in Stjørdalselva at Gudå, Nord Tøndelag; and modeled consequences of different water discharge at low temperatures] (In Norwegian). Report 191, Laboratorium for ferskvannsøkologi og innlandsfiske (LFI), University in Oslo, Oslo.

Jensen, A.J. Effekter av klimaendringer på laks i Norge. [Possible effects of climatic changes on the ecology of Norwegian Atlantic salmon (Salmo salar L.)] (In Norwegian). NINA Forskningsrapport 036: 1–21, 037 Trondheim, Norway (1992).

MathWorks. Image Processing Toolbox. The MathWorks Inc. (2001). Matoušek, V. Frazil and skim ice formation in rivers. In Proceedings of the IAHR Ice

Symposium 1992, Banff, Alberta (1992). Tesaker, E. Some hydraulic aspects of fish life under the ice. In Proceedings of the

15th International Symposium on Ice, Gdansk, Poland, IAHR (2000). Whalen, K.G., Parrish, D.L. and Mather, M.E. Effect of ice formation on selection of

habitats and winter distribution of post-young-of-the-year Atlantic salmon parr. Canadian Journal of Fisheries and Aquatic Sciences 56: 87–96 (1999).