IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Research article
erd

Development of an Emergency Discharging Device andan Early Warning System for Floods at Irrigation Ponds
SHIMIZU KATSUYUKI*
Faculty of Agriculture, Tottori University, Tottori, Japan
Email: shimizu@muses.tottori-u.ac.jp

FUKUDA YUKI
Graduate School of Agriculture, Tottori University, Tottori, JapanYOSHIOKA YUMI
Faculty of Agriculture, Tottori University, Tottori, Japan
Received 27 November 2015

Accepted 15 March 2016(*Corresponding Author)

Abstract The spillways of irrigation ponds in Japan should be repaired to safely pass the 200year flood event, which is the design criteria set by the government. However, extensive time isrequired to repair the spillways owing to the large number of ponds and the high repair costs.
Therefore, we developed a low-cost early warning system (EWS) to reduce the risk tohouseholds in case of floods, as well as a low-cost emergency discharging device (EDD) toprevent or mitigate these floods. The Yutani irrigation pond in Tottori, Japan was selected forthis study. The pond stores runoff from the catchment area and has no inflow from other basins.
A siphon tube with a diameter of 20 cm was employed as the EDD for the pond and thedischarge performance was evaluated. First, 60-min rainfalls at return periods of different years
were estimated. Then, the peak runoff and subsequent arrival time of each year’s 60-min
rainfall and the discharges from the spillway and siphon were estimated. The water balance ofthe pond was calculated using the peak runoff as an inflow element, and the discharges from thespillway and the siphon were used as the outflow elements. The results showed that the pond
will overflow if a 50-year rainfall event occurs under current conditions; however, it will notoverflow when the siphon is employed even if a 60-year rainfall event occurs. Since the siphon
discharge was not large enough to pass a flood event greater than 60 years, we developed an
EWS that informs villagers living near the pond when the water level of the pond reaches theselevels through an alarm lamp and an e-mail. Based on the results of the water balance analysis,the EWS provided information to judge whether villagers should be evacuated or not and thetiming of the evacuation in the case of heavy rainfall events if necessary.
Keywords siphon, probability of rainfall, peak runoff, arrival time, water balance

INTRODUCTION
There are 1,094 irrigation ponds in the Tottori Prefecture, Japan as of September 2014. Heavy rainfall
increases the risk of floods, which could cause damage to the villages located downstream of the ponds.
Two of the possible countermeasures against floods include facility improvements and management offlood preparation plans. The purpose of facility improvements is to construct spillways that will safely
pass the flood events, and proper flood management includes the preparation of hazard maps to show
evacuation routes as well as the water levels at different places and roads when the flood occurs. The
spillways of most irrigation ponds in Japan require repairs to safely pass the 200 year flood event thatmeans the probability of flood occurrence, once per 200 year, which is the design criteria set by theJapanese government (MAFF, 2015). However, due to the large number of ponds and the high repairⒸ ISERD15IJERD – International Journal of Environmental and Rural Development (2016) 7-1costs, extensive time will be required to repair the spillways of every irrigation ponds. Therefore, wedeveloped a low-cost early warning system (EWS) to reduce the potential risks in the case of floods, aswell as a low-cost emergency discharging device (EDD) to help to prevent the floods and mitigate any
damages that may be caused. The results of our research will assist with flood management plans inareas that still require spillway repairs.
OBJECTIVE
This study aimed to develop a low-cost EWS to reduce risks in the case of floods as well as a low-cost
EDD to help prevent or mitigate the floods. Forecasting or real-time monitoring systems are employedin many EWSs installed at rivers and reservoirs, though they are not often applied to irrigation pondsthat typically rely on water level monitoring and warning systems that can send alerts by sirens, lamps,
and/or e-mails when the water reaches certain levels. However, these systems do not relay information
related to the timing of evacuation to villagers living in the affected areas. Therefore, we developed anEWS that informs villagers living near the pond, through an alarm lamp and e-mail when the waterlevel of the pond reaches certain levels, and on the basis of the results of a water balance analysis, theEWS also provides information during heavy rainfall events to judge whether villagers should beevacuated as well as the timing of evacuation if necessary. The function of an EDD was also quantified
in this study to assess the capabilities of the device to prevent or mitigate floods during different
rainfall events.
METHODOLOGY
Study Area
The study area selected was the Yutani irrigation pond in Tottori City, Japan. The storage capacity andthe catchment area of the pond are 3,800 m3 and 0.082 km2, respectively. The pond receives and stores
runoff from the catchment area and does not have inflow from other basins. The residential area of thevillage is located only 200 m downstream from the pond.
Water Balance Analysis
To simulate the water balance and water level of the pond under heavy rainfall, 60-min rainfall eventsat return periods of 10, 20, 30, 40, 50, 60, 100, and 200 years were estimated using the Iwai method.
The hourly rainfall record over a 71-year range (1943–2013) was downloaded from the Japan
Meteorological Agency (JMO), and the top 30 rainfall events were used for analysis.
The peak runoff and associated arrival times of the 60-min rainfall event during each year wereestimated using the Rational equation and the values were used to simultaneously solve both the Talbot(Eq.1) and Kadoya–Fukushima formulas (Eqs.2 and 3), respectively:𝑎𝐼 = 𝑡+𝑏

Eq. 1
0.22

𝑡𝑝 = 𝐶 ∙ 𝐴𝑟𝑒 = 𝑓 𝑝 ∙ 𝐼∙ 𝑟−0.35
𝑒Eq. 2
Eq. 3

where I is the rainfall intensity (mm/h), t is the duration of rainfall (min), a and b are the constantparameters related to the meteorological conditions, tp is the peak flow arrival time (min), C is theparameter related to the land use conditions, A is the catchment area (km2), re is the average effective
rainfall intensity (mm/h), and fp is the peak runoff coefficient.
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IJERD – International Journal of Environmental and Rural Development (2016) 7-1

The Rational equation for determining the peak discharge from the catchment area and average
effective rainfall intensity is expressed as follows:
1𝑄 = 3.6 ∙ 𝑟𝑒 ∙ 𝐴Eq. 4

where Q is the peak runoff (m3/s). The discharges from the spillway and the emergency discharging
device (siphon) were estimated using the hydraulic formula as expressed in Eqs. 4 and 5. The siphon
tube was assumed to be 20 cm in inner diameter.
The discharge from the spillway was calculated using rectangular weir or orifice formulas
according to the water level. The EDD comprises a siphon tube that was 20 cm in diameter. Therefore,the average velocity of the siphon tube was estimated in consideration of all head losses owing toparameters such as friction and the curve of the tube. The formulas used in the calculation are
expressed in Eqs. 5 and 6:
3

𝑄𝑠 = 𝐶𝑠 ∙ 𝑏 ∙ 𝐻2

(if the water level is below 0.54 m)

Qs = 𝐶0 ∙ 𝑏 ∙ √2𝑔(𝐻21.5 − (𝐻2 − 𝐻1 )1.5 )Eq. 5(if the water level is over 0.54 m)

Eq. 6

where Qs is the discharge from the spillway, Cs and Co are the discharge coefficients for the rectangularweir or orifice condition, respectively, g is the gravity acceleration (m/s2), b is the width of the spillway(m), H is the water level of the spillway (m), H1 is the height from the water surface to the top of thespillway (m), and H2 is the height from the water surface to the bottom of the spillway (m).
The water balance and rate of increase of the water level of the pond were calculated using thepeak runoff as the inflow element and the discharges from the spillway and the siphon as the outflow
elements on a secondary basis. Due to the assumption of short and heavy rainfall, evaporation andinfiltration from the pond were ignored. The necessary information to create the height–volume curveof the pond was surveyed. The function of EDD was evaluated and the alert and warning water level ofthe EWS was set on the basis of the results of the simulation.
RESULTS AND DISCUSSION
Estimated Rainfall and the Peak Discharge
The 60-min rainfalls at different return periods; the arrival time; the effective rainfall intensity; and thepeak runoff discharge, are shown in Table 1. To meet the design criteria set by the government, the200-year rainfall intensity was estimated to be 85.4 mm/h, and the arrival time of the peak runoff wasestimated to be 34.5 min. The pond was assumed to have a spillway capable of passing discharges at
rates >2.10 m3/s.
Table 1 Estimated rainfall intensity and the peak runoff
Returnperiod
(y)
1020
30
50
100
200

Rainfallintensity(mm/h)
56.3
62.5
66.2
71.1
78.0
85.4

Arrivaltime
(min)
41.5
39.6
38.6
37.4
35.9
34.5

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Effective rainfall
intensity(mm/h)
53.9
61.5
66.2
72.4
81.4
91.1

Peakrunoff(m3/s)
1.24
1.42
1.53
1.67
1.88
2.10

IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Function of the Emergency Discharging Device
The water levels of the pond according to the different years of rainfall were simulated based on thewater balance discharge calculated on a secondary basis. Figure 1 shows the peak water level at
different years of rainfall with and without the EDD. As shown in the figure, the pond was notpredicted to overflow when the 30-year rainfall event occurred, regardless of the presence or absenceof the EDD. However, the pond was predicted to overflow during the 50-year rainfall event without thepresence of the EDD, while it was not predicted to overflow until a greater-than- 60-year rainfall event
occurred when the EDD was present.
9590
Peak water level (cm)

80706050403020Without EDD

10With EDD

010203050
Year

60100200Fig. 1 Peak water levels for different years of rainfall events,
where 95 cm refers to the top of the dikeFigure 2 shows a comparison of the discharges from the spillway and EDD. The EDD was observed todischarge more than the spillway during peak runoff, and when the water level reached the top of thespillway at 54 cm, the discharge from the spillway exceeded the EDD. When the maximum discharge
occurred, the EDD contributed to approximately 20% of the total discharge. The result of the waterbalance simulation indicated the requirement for an EWS to alert the villagers to be evacuated when agreater-than-60-year rainfall event occurs.
0.8
EDD

0.7

SpillwayDischarge (m3 /s)

0.6
0.5

0.4
0.3
0.2
0.1
00300

600900Time (s)1200

Fig. 2 Comparison of the discharges simulated for the spillway and the EDDⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Setting Alert and Warning Water Level of the EWS
The EWS has two water sensors at different water levels. The sensor set at the lower water level isconsidered as the alert water level to indicate the villagers to start preparing for evacuation, while theother sensor set to a higher water level is considered as the warning water level to indicate the timingof the evacuation. Based on the evacuation route found on the hazard map made by the villagers andthe Tottori Prefectural Federation of Land Improvement Association (2014), the time to evacuate fromthe houses to the designated safe places is estimated to be 10 min, with an additional 5 min assumed tobe necessary to prepare for the evacuation. Therefore, the warning water level can be defined as thewater level that is measured 10 min before the flood occurs (95 cm), and the alert water level can bedefined as the water level that is measured 5 min before the water level reaches the warning level. As
explained above, the pond will overflow when a greater- than-60-year rainfall event occurs. If the time
for the water level to rise from alert to warning is less than 5 min during a greater-than-60-year rainfall
event, then it should take longer than 5 min for the water level to rise from alert to warning during aless-than-60-year rainfall event. This means that the villagers can judge whether they need to beevacuated by the time it takes the water level to rise from the alert to the warning levels. The conceptof setting the warning and alert water levels is illustrated in Fig. 3.

Fig. 3 Concept of setting the warning and alert water levels, where A.W.L. indicates the alert
water level, and W.W.L indicates the warning water level
Table 2 Time required for the water to reach between two different levels
Water level
20 cm
30 cm
40 cm
54 cm
60 cm

30 cm
2 min 8 s
-40 cm4 min 19 s
2 min 11 s-

54 cm
7 min 27 s
5 min 19 s
3 min 8 s-

60 cm
8 min 52 s
6 min 44 s
4 min 33 s
1 min 25 s-

95 cm
18 min 40 s
16 min 32 s
14 min 21 s
11 min 13 s
9 min 48 s

Table 2 shows the time for the water level to reach 20, 30, 40, 54, 60, and 95 cm under a 60-year
rainfall event. The distance of 54 cm was selected instead of 50 cm because the top of the spillway is
54 cm, and this distance makes it easier for people to gauge the water level immediately. From thetable, the alert water level should be set lower than 54 cm to obtain more than 10 min for evacuation.
Supposing the warning water level is set to 54 cm, the starting water level will be 40 cm to result in arise to 54 cm in less than 5 min. However, the preparation time for evacuation is only 3 min and is tooless for people to prepare for evacuation. Therefore, we set the alert water level to 30 cm. FollowingⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2016) 7-1

that, if the time of the water level rise from 30 to 54 cm is less than 6 min, we can judge if evacuationneeds to occur.
Installation of the EDD and the EWS
The EWS and EDD were installed at the studied irrigation pond (see Fig. 4). The opening and closingof the 20-cm diameter siphon tube (KanaLine N. S., Kanaflex Co., ltd.) is controlled by an electric bulb
(Butterfly Valve Electric Actuated Type T-57, Asahi Organic Chemicals Industry Co., ltd.). The EWS
was settled at the dike and sends e-mails to registered people such as villagers, local government
officers, and university officials when the water level rises up to the alert and warning water levels andalso informs the villagers via an alarm lamp.
Alarm lamp

Water sensor

Manual valve

Electric valve

Solar panel

Modem and controller

Fig. 4 Photographs of the EDD (left) and the EWS (right)
CONCLUSIONAn EWS and EDD were developed to reduce the risk in case of floods and to prevent or mitigate thefloods at an irrigation pond that did not have a sufficiently large spillway to safely pass a discharge
caused by heavy rainfall. The developed EDD could not satisfy the criteria designed by the government
but could prevent against floods caused by less-than-60-year rainfall events. The EDD enhanced thedrainage function by at least 20% during flood conditions. The previous EWS had just informed therelevant people and agencies when the water level reached a certain level, but the newly developed
EWS presented in this work is a type of epoch-making device in terms of informing the timing ofpotential evacuations. Our results also suggested that multiple countermeasures such as a combinationof EDD, EWS, and hazard maps are required to prevent floods and mitigate flood damage to people.
ACKNOWLEDGEMENTS
The authors would like to express their deepest gratitude to the Tottori Prefecture of Japan for thefinancial support for this study.
REFERENCES
Japan Meteorological Agency: Search Past meteorological record: http://www. data.jma.go.jp/obd/stats/etrn/index.php (in Japanese)
Ministry of Agriculture, Forestry and Fisheries (MAFF) Japan. 2015. Design criteria of land improvement projectⒸ ISERD

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IJERD – International Journal of Environmental and Rural Development (2016) 7-1- Irrigation pond improvement. JSIDRE, p. 32, pp. 165-166 (in Japanese).
Yamamoto, H., Miyamoto, H., and Sawa, M. 2014. A case study of making a hazard map for irrigation ponds byTottori Prefectural Federation of Land Improvement Association. Annual Research Meeting on JSIDRE
Chugoku-shikoku Region, 97-99 (in Japanese).

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