SPRING 2000 LARGE FLOOD IN NORTH

Spring 2000 was marked by great floods in all parts of Ostrobothnia and . Especially bad situation was experienced in the water courses of the rivers , Pyhäjoki, and . In these rivers both an exceptional ice jam flood and an extra- ordinary water flood occurred. All three rivers are typical Ostrobothnian rivers. There are few lakes, and variation in water level and flow is great. Shores are low and vulnerable to floods. Also the size of these water courses is alike, the catchment area about 4000 km2 and the length of rivers about 100 km.

Article in the Journal MAANSIIRTO 5/2000 by Reino Enbuske, Heikki Nikkarikoski, and Heikki Savolainen, Regional Environment Centre

In all rivers mentioned above, extensive flood protection works have been done during many decades. At first in the 1950´ies and before that, the works were primarily clearing and embankments favouring agricultural needs. Later on since 1960´ies, artificial lakes have been built in the uppermost parts of the rivers, and natural lakes have been regulated in order to adjust discharges. A remarkable part of disadvantages caused by floods was eliminated by water construction, but damages caused especially by ice jam can still be considerable. In , due to economical and technical reasons, the flood protection works have been dimensioned for floods with frequency once in 20 years in agricultural areas, and once in 50 to 100 years in housing areas.

Works done in water courses

The total beneficial area of the flood protection works of the rivers Siikajoki, Pyhäjoki and Kalajoki exceeds 15,000 hectars cultivated land of which about 8,000 hectars belong to the Kalajoki area (Picture 1). Altogether, there are 16 regulated or artificial lakes in these water courses. The total regulation volume of those is 432 million cubic metres. In Table 1, the general information more in detail can be studied.

The artificial lakes were big projects in their time. In the earth dams of Uljua and Hautaperä reservoirs, the volume of excavated soil masses used was in each case more than one million cubic metres. The Uljua artificial lake has a decisive role in the regulation of the entire Siikajoki water course. It gives means to significant cut of flood peak in Siikajoki. The regulation volume of Pyhäjoki is entirely in Lake Pyhäjärvi that can take all flood waters from upper parts of the water course. The catchment area is relatively small which means that its impact on flood flow cannot be very significant compared to flood discharges in the whole river. In Kalajoki regulation, the central reservoir is the artificial lake Hautaperä in Haapajärvi. Also all waters discharged from Lake Reisjärvi are led through the charging canal to Hautaperä reservoir. Through another charging canal the waters from Kuonanjärvi also are led to Hautaperä. It is though possible to lead waters from Kuonanjoki as well as waters from Kalajanjoki directly through regulation dams to Lake Haapajärvi. Other regulation dams operated in the Kalajoki water course are in connection to regulated lakes or reservoirs or power plants.

The three water courses are regulated to benefit flood protection, power production, water pollution control, and the recreational use of waters. The general aims of regulation are profit for agriculture together with advantageousness of power production (winter time descending of water level in reservoirs), improvement of water pollution control (winter and summer time access of low flows), and better conditions for recreation and proper biotypes for fishes. The regulation permits are owned by the Regional Environment Centre of North Ostrobothnia. The local power companies, Vattenfall and Vieska Energia have committed themselves to take care of the regulation discharges in accordance with the water court decisions and guidelines by the environment centre. The power capacity of these three rivers totals to 19.6 MW and yearly energy to 52.6 GWh. More than one half comes from the river Kalajoki, and the rest splits even between the rivers Siikajoki and Pyhäjoki. 1 Picture 1. Kalajoki water course and its longitudinal profile 2 TABLE 1 GENERAL INFORMATION ABOUT THE REGULATED LAKES AND ARTIFICIAL LAKES

Lake Area Catchment Regulation Regulation area range volume p-a ( km2 ) F (km2) max ( m) max (M m3)

Siikajoki 1. Uljua* 28,0 1453 8,0 146,0 2. Iso-Lamujärvi 24,1 185 1,3 27,0 3. Vähä-Lamujärvi* 3,0 22 0,75 3,8 4. Kortteinen* 7,0 362 3,0 9,0

Pyhäjoki 5. Pyhäjärvi 126,0 690 1,25 137,0 6. Piipsjärvi * 4,1 552 sill 7. Haapajärvi 3,8 1960 1,45 4,0

Kalajoki 8. Kiljanjärvi 1,8 80 2,50 3,8 9. Reis-ja Vuohtojärvi 11,9 365 2,25 19,2 10. Korpinen * 3,0 30 4,5 5,2 11. Juurikka * 1,8 22 2,75 3,6 12. Kuona * 5,4 130 2,05 9,5

13. Hautaperä * 7,6 980 11,50 48,2 14. Haapajärvi 3,5 1460 0,50 1,6 15. Settijärvi * 4,2 193 2,50 9,4 16. Pidisjärvi 4,5 2200 1,3 5,0

*) Artificial lake

The Regional Environment Centre of North Ostrobothnia is responsible for maintenance of 20 completed projects including 16 dams that accord with category set by dam safety act and in addition other constructions, as follows: - earth dams 28 km - regulation dams 16 - canals 30 km - sills 32 - embankments 115 km - pump plants 31

The reacquisition value of these constructions and all equipment would be about 380 million marks.

Hydrological circumstances

The yearly precipitation in the area is around 550 mm, evaporation around 270 mm and mean discharge 8,6 l/s x square km. Around 45% or 200 mm of the precipitation falls as snow. The average maximum of water equivalent in snow cover is 105 mm at the turn March April. Dikes and clearings done in the catchment area have accelerated the flow forming especially in high flow situations. Artificial reservoirs and regulation in use have made flows more even and low flow requirements have increased flows during dry seasons.

Due to small number of lakes the variation of water levels and flows is great. E.g. at the gauging station Niskakoski situated in the lower part of Kalajoki (F=3025 km2, L=1.8%) observations have been made since1911. The lowest observed flow NQ = 0.0 m3/s, mean low flow MNQ = 1.5m3/s, mean flow MQ = 26 m3/s, mean high flow MHQ = 245 m3/s and highest observed flow HQ = 469 m3/s. Thanks to the regulation of Kalajoki, low flows have raised 2-3 m3/s. In areas being in natural state and having few lakes as Malisjoki and Vääräjoki areas, the relation between mean high flow and mean flow MHQ/MQ is 10-15. Lakes in the upper part of the water course and the regulation both cut the flood peak so that along the lower and middle parts of Kalajoki the relation MHQ/MQ is less than 10 and along the upper part only 2-3.

The greatest flood damages in the Kalajoki water course have been caused by floods originated by ice jam. The worst situation shows up when snow melts rapidly and the melting is accelerated by falling rain so that flows increase suddenly causing ice break-up. In this kind of case, the ice usually has not yet become thinner or weaker and is therefore gathering in an ice jam. Just in this way developed the situation in spring 2000. In a normal situation, as melting of snow is even, the ice-break can be delayed by storing melting waters in reservoirs. So the ice gets time to weaken and the risk of forming ice jam diminishes. 3 E.g. in the lower part of Kalajoki, the “ice-break flow” can be put down about25%, but in the middle part of the river even more than 50%. In addition, ice of the middle part is melted by the heat storage of Pidisjärvi by lowering evenly the water level in the lake evenly near to the regulation limit about two weeks before the melting season begins.

Flow and regulation models as well as river ice models (Kalajoki) have been made to serve water management of rivers and regulation operations in them. The flow models estimate for parts of the catchment area the inflow time series based on the given precipitation and temperature observations. Using water level, flow, and weather observations, and weather forecasts the model makes inflow prognosis for different points of the water course. The flow model includes also reservoir models and river bed models giving means to create water level and flow hydrographs of reservoirs and parts of a river bed. In the river ice model the flow estimation is combined with apart model describing heat balance, and surface, edge and frazil ice formation, and snow melt. This model can be used for studying the impact of inflow, river geometry, and ice cover on the flows and water levels in the model river part, and the impact of both weather conditions and the temperature of the inflow on the formation of ice cover and on snow melt.

The spring 2000 flood

The second half of year 1999 gave more than average precipitation. In December the precipitation was twice the normal. Also the beginning of the year 2000 continued more rainy than the average. Though a great share of the January precipitation came as water, the water equivalent of snow at the end of March was 25% higher than the average. The beginning of April continued rainy and the maximum water equivalent of snow was measured on April 4th being almost two weeks later than the average date of maximum water equivalent. The measured water equivalent 140 mm was approximately 1.5 times the average equivalent at this time. As there was much rain fall during the latter part of April and the temperatures were exceptionally high and no night frost existed the snow melted in a record short time causing both ice jam and water floods in the region.

precipitation daily mean temperature

°C long term average mm mm 1961-90 2000 10 36 160 8 32 140 6 28 120 4 24

100 2 20

80 0 16

60 -2 12

40 -4 8

20 -6 4

-8 0 0 JANUARYFEBRUARY MARCH APRIL MAY 1.4. 4.4. 7.4. 10.4. 13.4. 16.4. 19.4. 22.4. 25.4. 28.4. Picture 2. Water equivalent of snow in Kalajoki water course Picture 3. April temperature and precipitation in

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The river Kalajoki

The spring 2000 floods were confronted by discharging the regulation reservoirs in the normal way to achieve the lower limit level set by regulation guidelines, by sawing ice in the worst ice jam sites, by exploding ice under rapids, and by digging ice. The artificial reservoirs and the regulated lakes offered altogether about 90 million cubic meters´ volume for the melt waters. Along the lower part of the river Kalajoki, ice sawing has been used as prevention means in places where the flood risk is high and where the promoted moving of ice does not cause flood risk in the downstream part of the river. In spring 2000, ice was sawn at the main village of Kalajoki, in places called Tynkä and Kääntä and in the centre of . The length of openings sawn reached in all to 20 kilometres.

The sawing was done by equipment developed in the regional environment centre of West Finland / . The track chain driven machine includes an in build, on hydraulics based rotating saw. This equipment is able to saw a 19 cm broad opening through up to 130 cm thick ice cover. On ice having thickness of 60 to 70 cm, the working speed is 1.3 km/h. In the places Tynkä, Alavieska and Vääräjoki/Kamunen, the ice formations in still water under rapids were weakened in advance by exposing and digging.

Picture 4. Ice saw Railo is one of the products of equipment development by the former Central Ostrobothnia Regional Environment Centre. The machine is 7.3 m long and 3.2 m wide having weight of 8.0 tn.

The water levels and discharges of the Kalajoki water course started an even rise since beginning of April. The warm period and reigning water made the discharge rise roughly since April 14th, and the maximum flood was achieved overall in the watershed between April 23rd and 27th. On April 24th, the at Niskakoski monitoring site recorded flood maximum of 414 cubic metres´ discharge means the second greatest discharge ever recorded during the observation period since 1911. According to Picture 5, the high flow in spring 2000 corresponds to once in 45 years high flow. The snow melt waters were stored to the reservoirs since April 14th. During the flood maximum, the total storage use of the reservoirs was about 130 cubic metres pro second which means that without regulation the flood maximum in the river Kalajoki would have been greatest ever recorded at Niskakoski. Picture 6 shows flow values in the upper part (Oksava), the middle part (Padinki) and the lower part (Niskakoski) of the River Kalajoki as well as the combined actual storage in the reservoirs.

Picture 5. The river Kalajoki / Niskakoski high flow recurrence intervals in years. 5 The main regulation reservoir of the river Kalajoki, the Hautaperä artificial lake, was full in record short time. The maximum rising speed of water level was more than 1.5 metres in 24 hours. The inflow to the reservoir was so huge that passing discharge was needed nearly all the flooding time. During the flood peak, the Hautaperä reservoir alone stored 80 cubic metres water pro second. Picture 7 shows water levels of the Hautaperä reservoir during the first five months of the year 2000.

Q (m3/s) 500

400

300

200

100

0

100

200 2 10 12 14 16 18 20 22 24 26 28 30

Niskakoski Padinki Oksava Altaat

Picture 6. Flow of the river Kalajoki and storage volume of reservoirs (Altaat) at the turn of April and May.

W N43+m OBSERVED WATER LEVEL 100 99 98 97 96 95 94 93 92 91 90 89 JANUARY FEBRUARYMARCH APRIL MAY

Picture 7. Water levels in the Hautaperä reservoir in January – May 2000.

6 The lower parts of the rivers Kalajoki and Vääräjoki have always been under thread of ice jam. After quite a long chain of rapids there is often a still water being broader in the upper part so that the ice blocks falling from the rapid can't find their way downstream but stay jammed in the still water and cause ice jam. Even if the ice in spring 2000 was thinner than in average, it didn't diminish in time, due to the rapid escalation of discharge and the cloudy weather but caused heavy ice jam in lower part of the river Kalajoki and in the rivers Vääräjoki and Malisjoki. Worst situation developed in the centre of Kalajoki where 7 one-family-houses were damaged. Around the lower part of the river Vääräjoki, the flood caused by ice jam isolated tens of production units and broke road connections. As the ice blocks rose from the water course in Tilvis/Kalajoki, power poles were broken. One hospital was in danger because of the ice jam that developed in the lower part of the river Malisjoki. Real estates, roads, bridges etc. were damaged by ice jam, costs being calculated arising to several million marks.

In spite of the fact that damages were considerable, the combating operations done must be seen successful and remunerative. Without combating works, instead of ten some fifty homes had been watery and many cow stables and piggeries had needed to be evacuated. The entire field team of the regional building personnel was ordered on duty and they worked the whole flood week over Easter having practically only 4 hours sleep pro night.

The entrepreneurs showed real willingness to co-operate so that in spite of dangerous working conditions and the holidays enough caterpillars were available. Using machines replaced in several cases blasting operations and did lighten threatening situations so that damages were avoided or diminished. Based on the experience gained, caterpillars will probably be used also in the future in demolition of ice jam. In addition, the need exists to develop in co-operation with entrepreneurs safety at work, working methods, and technical aid equipment. Co-operation with rescue authorities worked well out even though critical ice jam situations followed each other in one site after another. Because of lack of other experts, firemen had to be used on some sites also in the real combating activities to take care of preparations for blasting works. Their own work in charge of rescue operations and safety claimed day and night work, too.

Digging machine breaking ice jam.

The exceptionally great discharges caused water floods on the entire area of the Kalajoki water course. The largest united flood areas were formed in the middle part of the Kalajoki, to the Malisjoki, to the lake drainage area of Kalaja, in the middle part of the Vääräjoki, and to the Siiponjoki. All flood areas were filmed from air and the flood levels were marked in the field. The estimation was that altogether near10.000 hectars land was under water and of those land units larger than100 hectars round 5.000 hectars. The most embankments built for flood protection were able to keep the water in the main water course, but since the drainage constructions for agriculture ( ditches, pumping stations) also at the River Kalajoki have been planned for once in 20years floods, even the embankment areas had floods. Damages to the embankments and drainage systems were relatively insignificant, but the exceptional flood caused along the river more serious erosion than usual. All damages to agriculture will exceed in the Kalajoki area up to several million marks.

The River Pyhäjoki

Due to the fast melting of snow, along the River Pyhäjoki damages caused by extraordinary high discharge, and high flood combating costs could not be avoided. The Pyhäjoki discharge was second highest during the past hundred years.

Along the Pyhäjoki there are 58 km riverside embankments that demand continuous maintenance. Need of extra repair works became evident due to the spring 2000 grand-scale flood. The worst situation was experienced at Kenkimä embankment (length 4 km) in lower part of the Pyhäjoki. Between April 24th and 28th, the embankment leaked in 10 different places. All of them were filled temporarily with moraine driven to those points. The leaking was localized by using caterpillar bucket underwater pushing around along the embankment until at the normally dry side of the embankment water coming through had grey colour. Filter geotextile could not be used in reparations because of hurry and strong flow. Moraine happened to be for sale in a farm having excavated land piled up. Later on, moraine had to be taken as emergency work from the moor area close to the embankment. If the embankment had broken the housing area of Merijärvi had got under flood. Picture 8 shows the principle of the temporary fixing of embankment.

The worst flush point of the embankment Kenkimä was found by a young man driving motor bike along the river to make observations. He reported the leakage to the working crew of the site and might so have saved all the Merijärvi housing area from significant flood damages. In many embankment areas water came over. This happened especially at those embankments that had not yet been under basic maintenance repair. The method used in Kenkimä did not work in another site where the fast flow and the steep slope made the moraine run away with the water. The leakage was stopped by a cocktail mixed half and half of moraine and jagged stones. The mix was made where the material was loaded. The flow first took away the upper fine 7 material but the jagged stones stayed and covered the deeper moraine layer. In addition, in this case the dry side of the embankment was provided with filter geotextile and moraine.

Picture 8.

Breaking of the Pyhäjoki embankments spring 2000 was explained by one or several reasons. The embankments had been made in nineteen fifties by men and horses, and the material used might have included organic components that weakened the embankment. Normally the embankments are during the flood period still frozen which probably means additional strength. In spring 2000 there was practically no frost in the ground. The embankments have been planned against short time water pressure only. In this case, water stayed record high several days.

The river Pyhäjoki, Merijärvi area ice. 8 Based on the experiences of the spring 2000 the question will be discussed whether the embankments that are meant to safeguard housing areas shall be strengthened to the earth dam level and whether danger risk analysis have to be done for those. The work has already been started for Kenkimä embankment by the dam experts of FEI together with others.

The past flood season taught that preparations for floods like those in spring 2000 must be something better than arranging reserve sites offering moraine and jagged stones or improving connections to the embankments. One of the most profitable alternatives to solve the problem could be building of passing and turning areas that could bemused as reserve site for soil transport. Such kind of areas already have been built to those embankments that had basic maintenance reparations. The reparation work in the Kenkimä case was hampered just by difficulties in material delivery and by lack of passing and turning points.

The interest of the media was great in connection with the Pyhäjoki embankments, and there was an appeal for immediate notice in case the Kenkimä embankment would break. Thanks to competence of the flood control organization and its day and night duty, the area of the river Pyhäjoki was spared from damages of millions of marks.

The River Siikajoki

Along the Siikajoki, ice jam did not cause significant problems, but water flood developed there, too. The regulation of the reservoir Uljua succeeded so that the biggest cut off was timed to the flood peak, and the flood along the middle and lower parts of Siikajoki was cut considerably. The flood maximum was gained April 27th, the flow being 310 cubic meters per second. The same time the Uljua reservoir stored 230 to 250 cubic meters per second which means that the discharge of the lower part of the Siikajoki had without the reservoir been 550 cubic meters per second. In spite of the successful regulation the Mankila flood area had at worst 3.500 hectars arable land under water. If the storage volume had not been available the water level in Mankila would have been more than 0,5 meters higher and the flood areas and damages much more greater. Damages would have occurred elsewhere along the river, too, and on some areas water would have risen more than one meter higher and the damages on the riverside would have developed much more severe.

Summary

The exceptional developing of the spring 2000 flood showed that the flood protection works completed were functioning quite as planned. By regulations an essential part of flood maximum was cut of successfully. The role of Hautaperä reservoir in the river Kalajoki regulation and the role of Uljua reservoir in the regulation of the river Siikajoki regulation were decisive. Later on, the Kalajoki distance management and control system under construction together with model development will make especially the flood time operative management better and more effective. If the maximum spring flood in the lower parts of the Rivers Kalajoki and Pyhäjoki should be decisively cut down by regulations, the precondition would be building of artificial lakes, being at least of the same size as the Hautaperä reservoir, in the middle part of the rivers. This would mean at least one hundred million marks investments for each. For this there are no realistic opportunities, but smaller projects are needed concentrating in local problematic points. The damages caused to properties by ice jam and high flows pointed out the aim without delay to plan and realize flood protection works just in these places. Admitting that R&D of prevention methods against ice jam is important, the priority lies on finding steady solutions for these places. Keeping the existing constructions in good shape as required should also be an important aim. The water construction property amounting to about 400 million marks would need for its economical maintaining yearly a minimum of 4 million marks. The grants have been so far half of that. The spring 2000 flood gave valuable information for developing the operative management and basics i.a. for planning flood protection. The most valuable gain from the flood areas and flood levels might be discovered in the future in connection with land use planning. New house building shall be guided away from flood areas and all constructions suffering of humidity shall be planned high enough. The flood in spring 2000 in Finland and the large flood of July in the middle parts of Sweden proved that flood protection is needed and that careful precaution for floods is awarding. Flood protection constructions should be maintained properly and flood control plans as well as dam safety proceedings shall be updated.

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