| Budget Amount *help |
¥4,000,000 (Direct Cost: ¥4,000,000)
Fiscal Year 2002: ¥1,300,000 (Direct Cost: ¥1,300,000)
Fiscal Year 2001: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2000: ¥1,200,000 (Direct Cost: ¥1,200,000)
|
|---|
| Research Abstract |
The Rokugo alluvial fan lies around 39°25' N and 140°34' E in northern Japan. The distance between the proximal fan on 90 meters above sea level and the distal fan on 45 meters is about four kilometers, Unconfined aquifer of the fan consists mainly of gravel, of which hydraulic conductivity is in order of 10^0〜10^<-2> cm/sec and specific yield is over 20%. The depth of the aquifer is over 100 meters in the center of the fan. About 70% of the land surface is used for paddy field. About 6,000 inhabitants live in the area of the distal fan. They privately posses well, pump and water supply system of their own in each homes. There are relative small 70 water springs which keep environment comfortable, and used for domestic purposes.
Annual groundwater levels regularly change, I.e. high water levels occur during irrigation period from May to August, and low water levels occur during nonirrigation period, especially around the time when snow cover reaches maximum.
Artificial recharge for aquif
… More
er using four basins has been performing during nonirrigation period in order to enhance groundwater. The basins. Nos. 1-4, were constructed on the central part of the fan.
We show here effects of artificial recharge on the formation of groundwater mounds under the basin No.2 which equips 2,120m^2 bottom area and 3m depth. The results are based on the cases of artificial recharge which have done three times, first: from September 8 to November 10, 1998 (63 days), second: from November 15, 1998 to April 5, 1999 (141 days) and third: from April 19 to April 29, 1999 (10 days). Water of 100 l/sec was supplied to the basin.
The followings are results. From 1 to 3 were obtained through the measurements using an observation well located at 2.3m west from the edge of the basin.
1. Initial groundwater revels recorded ca. 57.50m over sea level in each of the cases.
2. After beginning of the water supplies, the maximum groiundwater level of 60.39m appeared in 43 hours for the first case, of 60.39m appeared in 56 hours for the second case and of 60.66m appeared in 172 hours for the third case.
3. Groundwater levels began declining after stopping the water supplies. The level of 2.49m decayed in 47 hours for the first case and 3.71m decayed in 91 hours for the second case. For the third case, the decay appeared not so much because infiltration rate increased caused by snow melting.
And 4. The artificial recharges formed groundwater mounds under the basin. In the area of western direction of the basin, water tables were raised due to the formation of the groundwater mounds.
5. Artificial recharge for aquifer has been enhancing groundwater cycle in the Rokugo alluvial fan and there realizing sustainable groundwater use. Less
|
