Water Loss in the Benanain River from Temef Dam to Haekto and Benanain Weirs in East Nusa Tenggara

Water loss always occurs in the process of delivering water from the water source to the user structures. The Benanain River, which is a natural channel, is a means of carrying water from Temef Dam to Haekto Weir to irrigate Haekto Irrigation Area and Benanain Weir which is used to irrigate Malaka Irrigation Area. The length of the river from Temef Dam to Haekto Weir is 23,689 m and from Haekto Weir to Benanain Weir is 21,673 m with a total length of 45,362 m. Along the way, water loss occurs due to the influence of evaporation, percolation, river cross-sectional area and river length. This research looked for water loss that occurred in the river and obtained an average result for the Temef Dam - Haekto Weir section of 0.243 m3/second and for the Haekto Weir - Benanain Weir section of 0.183 m3/second.


Introduction
Water loss is a serious problem in the water distribution system.High levels of water loss are caused by various technical factors as well as poor management.The amount of water lost from distribution systems in the world is very large and is estimated at 48 billion m 3 per year [1] Various methods have been used to study the causes of water loss and how to overcome them.Likewise, water loss in rivers downstream is used for irrigation.The longer the river reaches the intake structure, the greater the potential for water loss along the way.
Timor Island, Indonesia has a lot of potential irrigation areas which are extensive, including Haekto and Malaka Irrigation Areas.Until now, this area has not been developed even though it has large water sources and a large area to be developed.For this reason, in the 2020 Fiscal Year, the Government through the Ministry of Public Works and Public Housing c.q.The Nusa Tenggara River Region II Work Unit, Planning and Program Activities carries out the work " System Planning Study for Haekto and Malaka Irrigation Areas as Utilization of the Temef Dam in North Central Timor and Malaka Regencies" as a response to the community's need for water sources and land that can be cultivated.This area is an area with little rainfall, where the dry season is longer than the rainy season.So, the reliability of water in this area for irrigation water comes from the Temef Dam which is channeled through the Benanain River.Considering the long river before arriving at the destination irrigation areas, it is suspected that there was a lot of water loss along the way.This research tried to analysis the amount of water loss.

Research Methodology
The analysis water loss was carried out by comparing the water discharge released from the Temef Dam, with the estimated water loss that occurred along the way due to the influence of evaporation, percolation.This research method can be seen in the flow chart in Figure 1.

Study Location
The location used as the object of this research is the Benanain River channel from Temef Dam to Haekto Dam and Benanain Dam which is located in North Central Timor Regency and Malaka Regency for + 45 km length.The research location can be seen in Figure 2.

Hydrometeorological Conditions
Like other areas in Indonesia, North Central Timor Regency and Malaka Regency also have a tropical climate characterized by two seasons, namely summer and rainy season.The rainy season is between November -March, while the summer or dry season is between May -September.Climatological data located and adjacent to Haekto and Malaka Irrigation Areas are the Atambua and El -Tari Climatology Stations from year 2015 to 2017.Available climatological data includes air temperature, air humidity, wind speed and duration of sunlight.The average of climatological parameter from the Atambua Climatology Station and El-Tari Climatology Station is presented in Table 1.

Water Availability
The location of this study is located on the Benanain River with a total watershed area of 3,169 km 2 , which each watershed shown in Figure 5.The calculation of water availability in this study is divided into three watersheds, namely: Temef Dam Watershed, Haekto Weir Watershed and Benanain Weir.The water allocation for half-monthly irrigation from the Temef Dam can be seen in Table 2, which the data was got from Design Report of the Temef Dam Design to get certification [2].This allocation represents the availability of water from the dam for an irrigation area of 4800 ha as shown in Figure 6.

Water Loss
Evaporation and seepage are the most important forms of water loss in open channels [3].Evaporation losses depend on the free surface area, whereas seepage losses are a function of channel geometry.
where: Clay content (%) = the weight percentage of soil particles with a size smaller than 0.005 mm I = coeficient, 1 for sandy soil, 1.5 for loam, 2.00 for humus, 2.5 for clay.
The length of the Benanain River to Haekto Weir is 23,709 meters and Haekto Weir to Benanain Weir 21,673 meters.The cross-sectional width of the Benanain River at the study location is around 40 -50 meters.A scheme of the average discharge in the Benanain River can be seen in Figure 7.
The distance from the downstream of the Temef Dam to the upstream of the Benanain Weir is quite far, namely 45.38 km, resulting in a loss of water flow in the drainage.The calculation of water discharge losses is taken based on the values from the evaporation and percolation calculations.Evaporation is a physical process that changes a liquid or solid material into a gas and percolation is the downward movement of water from an unsaturated area into a saturated area.Evaporation calculation are shown in Table 4, figures of evaporation are shown in Table 5., and the vertical percolation rate value is taken as 2 mm/day for clay soil.
In the course of the flow of water released from Temef Dam with additional water supplies from existing sub-watersheds to Haekto Weir and Benanain Weir are as follows in Table 6.Meanwhile, water loss on the Benanain River section from Temef Dam to Haekto Dam and from Haekto Dam to Benanain Dam is as shown in Table 7.Average water loss from December to.November in the river section between Temef Dam and Haekto Dam is quite large, namely 0.242 m 3 /second.From Haekto Dam to Benanain Dam it is 0.183 m 3 /second.
According to FAO Aquastat 2015, in India, about 91% of water is used for Agricultural purposes and 45% of it is lost due to loss of agricultural distribution.The biggest loss is due to seepage [7].The research results show that the total loss of irrigation water from the 79.90 km long Almanna canal reached around 16.05 million cubic meters per month, or 23.90% of the actual discharge.Water lost through seepage alone reaches around 15.95 million cubic meters per month, or 99% of all irrigation water lost [8].

Conclusions and Recommendations
Water losses that occur in the Benanain River due to the influence of evaporation and percolation are as follows: x From Temef Dam to Haekto Weir, which is 23,689 meters, the average water loss is from December to November was 0.242 m 3 /second.x From Haekto Weir to Benanain Weir, which is 21,673 meters, the average water loss is from December to November was 0.183 m 3 /second.x Considering that seepage is great, and water loss due to seepage is a function of channel geometry, in order to minimize water loss in open channels, it is necessary to pay attention to optimal channel cross-section design.x Several soil investigations on river bed in certain distance are needed to see soil properties, so figure of seepage along the river will be more accurate.

Figure 2 .
Figure 2. Research locations in the North Central Timor and Malaka Regencies.The structures that utilize water from the Benanain River released from the Temef Dam are the Haekto Weir in Figure3and the Benanain Weir in Figure4.

Figure 5 .
Figure 5. Area of each sub-watershed in the Benanain Watershed.

Table 6 .
Computation of Water Loss Along the River.

Table 2 .
Availability of Temef Dam irrigation water.
Source: Certification for the Design, Addition Geological Investigation and Hydraulic Model Test Temef Damon South Central Timor.Regency, 2017.

Table 7 .
Water Loss in Benanain River Section.