Analysis Of Water Availability In The Environmental Water Sources Of The Aikmampat River Sub-Region In Fulfilling The Need For Clean Water In The South Part Of Lombok Island

Clean waters infrastructure functions in utilizing water resources for the general public. General planning for clean water development in this study is focused on water resource management in the form of stewardship, provision, use, development, and exploitation of water resources considering that the social, environmental, and economic functions of water resources cannot be separated. To estimate water availability for biota or ecosystems, we use the discharge at Q-95% at each weir. To analyze waters availability for biota, we refer to the flow duration curve graph. We have calculated the water balance for the Lingkung sub watershed of Aik Mampat, taking into account the surface water sources. The water balance has been calculated under two conditions: existing conditions (which include needs of irrigation and existing water needs of raw) and planned conditions (which consider the development of a drinking water management system). The level of service in the south coast area for 5 sub-districts in the development plan year was obtained at 150 l/s and a maximum of 270,75 l/s in the plan year. The maximum irrigation water requirement is 320 l/s with an average of 50 l/s. The water balance in the Aikmampat Sub-watershed (Lingkung surface water source) saw a decrease in the minimum FK (Reliability Factor) from the existing condition of 40% to 25% (plan condition). Water rotation arrangements in the spider channel need to be carried out, especially in June and July.


Introduction
East Lombok Regency is a regency located in the southern part of Lombok Island, within West Nusa Tenggara Province, with very dynamic development.This dynamism can be seen in the demographic aspects, social aspects, and economic aspects of East Lombok Regency.In terms of demographics, it can be seen from the growth and development of the population in East Lombok Regency.Based on East Lombok Regency in Figures 2020, the population in East Lombok Regency in 2020 was 1,325.2thousand people with a population growth per year 2010-2020 of 1,77 percent.
The Mandalika Special Economic Zone has spurred rapid tourism development in the southern of Lombok Island, Creating a buffer area in South Lombok has positively impacted the local economy and community's quality of life.This of course requires infrastructure improvements, especially clean water services.However, the availability of water is very small and supported by the Elnino phenomenon and 1321 (2024) 012022 IOP Publishing doi:10.1088/1755-1315/1321/1/012022 2 the long dry season that has hit, unequal water distribution causes problems in southern East Lombok Regency.
As quoted on ntb.idntimes.com,August 2023, the East Lombok Regency Regional Disaster Management Agency, stated that there are 11 (eleven) villages in Southern Lombok such as Keruak, Jerowaru, Sakra, East Sakra, West Sakra, and surrounding areas affected by drought and hardship.to get clean water.The lack of clean water sources means residents have to buy water sold by private parties [13].The head of the Regional Disaster Management Agency in West Nusa Tenggara expressed the same message, in his quote to bali.bisnis.com, in in June 2023, that apart from the government supplying water with water tanks, the people of South Lombok are currently also forced to buy water from the private sector for Rp.3500,-per jerry can.This is very burdensome for residents, so special attention and permanent treatment from the Government is needed to overcome this [11].
According to Fathul Rakhman and Moh Tamimi, 2019, in their article, every long dry season, in the Southern part of East Lombok Regency, especially from August to November, this area becomes a regular area for getting supplies or delivery of clean water from the Regency and Provincial governments in terms of at the Regional Disaster Management Agency.Surrounding water sources such as local wells are starting to dry up and the Regional Drinking Water Company's drinking water pipe network has not yet reached all service areas, which has resulted in drought [12].
In providing clean water services, of course, it must be balanced with the availability of raw water which is the main source for providing clean water.Raw water sources are water sources to fulfill water needs.Raw water needs are water needs whose fulfillment is intended for daily needs, both for household (domestic) purposes, for industry, for agriculture, and animal husbandry.Evayanti, R., & Sugiharta, S., 2021, on meeting raw water needs in the Mandalika Special Economic Zones through the Pengga Reservoir and Batujai Reservoir in deficit conditions with a reliability factor (FK) of 51% -55%, so that regulation is needed operating pattern [6].Evayanti, R., 2022, the need for clean water in the South Coast Region of East Lombok Regency is 136.66 l/s [7].
The northern part of East Lombok Regency is a wet area where there are many raw water sources, but on the other hand, the southern part of East Lombok Regency is a very dry area due to the lack of raw water sources.Due to these unequal conditions, the government has made various efforts to equalize clean water services and plans to fulfill the water requirements in the Southern of Lombok Region.Based on the fulfillment of various needs for raw water, it's necessary to conduct a water balance analysis study in the environmental water sources of the Aikmampat River Basin, East Lombok Regency.

Research Problem Formulation
The research problem is to determine the amount of clean water required on Southern Lombok Island, as well as to evaluate the water balance condition in the surface water sources of the Aikmampat Sub-watershed after being utilized as a source of clean water.

Research Objectives and Benefits
This research aims to understand the high demand for clean water in the southern region of Lombok Island.It also aims to determine the current state of water balance in the surface water sources of the Aikmampat sub watershed after being utilized as a source of clean water.Meanwhile, the benefit of this research is that it provides an overview of plans for handling drought disasters on the Southern Island of Lombok.

Research Sites
The research location is in East Lombok Regency, in Sikur District as a water source area, and 5 (five) Districts as planned service areas, namely Sakra, West Sakra, East Sakra, Keruak and Jerowaru Districts.The research location can be seen in Figure 1, below.

Data Collection 4.2.1 Primary Data
Primary data is data carried out by direct measurements in the field.In this case is instantaneous discharge data.Discharge measurements are carried out using a water speed measuring device using a floating object.Equipment used includes measuring ropes, stopwatches, and floating objects.Discharge measurements in this research were carried out 2 (two) times in the rainy season on 20 December 2022 and in the dry season on 15 June 2023.The steps for measuring discharge include [16]: a. Choose a good location in a body of water or river with a width, depth, slope, and speed that is considered constant, along approximately 1 (one) meter.b.Throughout the discharge observation area, make sure there are no obstacles or obstructions.c.Start measuring the drop of the floating object that has been tied with a 1 (one) meter long rope at the same time as starting the stopwatch.d.Stop the stopwatch when the floating object has passed the 1 m observation point.e. Measure the width and depth of the water along the observation point.

Secondary Data
Secondary data is obtained from related agencies, data is collected based on analysis needs.Secondary data includes: a. Rainfall data for the last 20 (twenty) years at the rainfall post influencing the study location, was obtained from the NT-1 River Basin Office.b.Climatology data for the last 20 (twenty) years at the climatology post influencing the study location, was obtained from the Meteorology, Climatology and Geophysics Agency of West Nusa Tenggara Province.c. Population social data for the last 10 (ten) years at the study location was obtained from the East Lombok Regency Central Statistics Agency.d.Data on Irrigation Area Planting Patterns at the study location was obtained from the East Lombok District Agriculture Service.e. Topographic maps at the study location were obtained from the NT-1 River Basin Hall.

Analysis of Raw Water Availability
Water availability is a source of meeting the water needs of living creatures, it can come from rain, water through surface flows, and groundwater.The mainstay of discharge analysis used is water balance.In the water balance method, monthly rainfall, evapotranspiration, soil moisture, and groundwater storage are calculated to calculate the monthly discharge [14].The water balance model used in this analysis is the FJ Mock model.The main components of the Mock model calculation are the calculation of rain and evapotranspiration, water balance on the soil surface, and soil storage.(Mock, 1973) [9].F.J. Calculation method Mock describes water that falls on the surface of a watershed, some of which will undergo an evaporation process, some will become direct runoff and some will be infiltrated into the ground.If the condition of soil moisture capacity (Soil Moisture Capacity) is met, percolation will occur, that is, underground water will seep down through small spaces between soil particles and rocks into the saturated aquifer to become groundwater or groundwater which will later become base flow.Rainwater that falls in a watershed will be transformed by the watershed system and will ultimately flow to the river in that watershed [10].

Analysis of Clean Water Needs
Analysis of domestic water needs is an important aspect of analyzing future water needs.Analysis of future water needs for the domestic sector was carried out using the basis of population growth analysis in the study area [8].So we can know that to know water needs in the future we need to know the current population and population increase.

Analysis of Irrigation Water Needs
The planting pattern will provide an idea of the type and area of plants that will be cultivated in one year.In this analysis, the modified Penman Methodology is used, by calculating the reference evapotranspiration (Eto), the reference evapotranspiration (Eto) whose value is known, then multiplying it by the plant coefficient to obtain the consumptive use (Etc) value [1].With other factors that support the calculation of irrigation water needs, such as effective rainfall adjusted to the type of plant (paddy/ secondary crops), the amount of percolation from a place is assumed and then determines the planting pattern.After that, by using the formula for finding irrigation water needs, you will get the water needs on the land, by adding channel efficiency, the water needs at the source can be determined [15].
Calculation of water requirements in rice fields is influenced by several factors, including conditions of the irrigation area, several factors, including evapotranspiration, soil preparation, crop coefficient, planting patterns, percolation, effective rainfall, and irrigation efficiency.
The water required during the soil preparation period is used to saturate the soil to help facilitate the soil processing process and maintain soil moisture levels according to needs at the time of planting.Analysis of water requirements for rice plants during water layer replacement due to evaporation and percolation during the 30-day soil preparation period.The depth of water required for soil preparation is 250 mm, in other words, 8.33 mm/day based on the average type of soil in Indonesia and compared with soil conditions and slope/soil slope.Secondary crops do not require special land preparation after 6 planting the first rice, so they do not require the addition of special water for land preparation, if necessary, especially in very dry areas, to loosen the soil for easy land preparation and provide adequate soil moisture for seeding, irrigation water added a little about 50 mm [18].
Consumptive use refers to the act of replacing lost water layers from evaporation, from plants (transpiration) and free water surfaces (evaporation) [17].The plant coefficient used to calculate consumptive use varies depending on the plant type and age, as shown in the table below : The process of water flowing into the top soil layer as a result of water intake is called infiltration.Water that seeps into the soil will be absorbed until field capacity is reached or all the soil pores are filled with water and the rest will continue to move downwards as percolated water.
Percolation is a condition where if the water infiltrating a place at a certain time exceeds the field capacity/soil pores and is saturated, then the excess will continue to move underground.Percolation depth is the loss of irrigation water that occurs when water is filled in rice fields due to flowing through the soil layer in the plant root zone into the saturated soil layer, in this process the water cannot be utilized by planting.The depth of percolation is influenced by the depth of the water layer, the type of soil, and the slope of the land slope.
Based on KP-01 Irrigation Planning Criteria, the amount of percolation in clay soil with good puddling, the average percolation rate is 1 -3 mm/day.The percolation rate will be higher in lighter types of paddy soil.In general, the type of soil in the upstream part of the Aikampat watershed has a clay/dusty clay texture with a fine texture so that in calculating water requirements a percolation figure of 2-2.5 mm/day can be taken [2].
Replacing the water layer is needed in rice cultivation to replace the water layer needed when planting seeds and fertilizing (making it easier to absorb fertilizer by plant roots).The amount of water replacement used is 3.33 mm/day.Meanwhile, cultivating secondary crops does not require changing the water layer due to different plant culture practices [20].
The height of the rain expressed in mm determines when to start the first planting and also determines irrigation water needs, for planning irrigation water needs and effective rainfall.According to KP-01, effective rainfall calculations are based on semi-monthly (15 daily) reliable rainfall.
Several factors that influence the amount of water for irrigation include the type of plant, type of soil, how to provide the water, how to cultivate the land, the amount of rainfall, the time needed for planting, climate, maintenance of water structures, and so on.In rice fields, water requirements can be calculated using the following formula [5].NFR = Etc + P + WLR -Re (6) whital : NFR = Netto Filed Water Requirement (mm/day) Etc = Evaporation of plant (mm/day) P = Percolatoin (mm/hari) Re = Effective Rainfall (mm/day) WLR = Replace the water layer Irrigation water requirements are calculated using the following formula: IR = NFR : Ef (7) whital : IR = Irrigation water needs (mm/day) NFR = Water needs in rice fields (mm/day) Ef = Efficiency consisting of efficiency in tertiary, secondary, and primary channels and buildings

Water Balance Analysis
Water balance is a calculation of inflow and outflow (water loss) in a certain period.To calculate the water balance in a watershed, the analysis carried out is to calculate the water needs in the watershed, in this case, the irrigation water needs of each irrigation area (DI) served by each weir which influences the watershed system.Apart from calculating water needs in the watershed, water availability in the watershed is also calculated, and then an analysis of the water balance in the watershed is carried out [19].
In the current stage, the analysis of the water balance is evaluated based on the K factor.This involves comparing the available discharge with the irrigation demand discharge [3].The following criteria are used to analyze the water balance:: 1.When there is a continuous supply, the K factor should be between 0.75 and 1.00.2. When turning in the tertiary channel, the K factor should be between 0.50 and 0.75.3. When turning on the secondary channel, the K factor should be between 0.25 and 0.50.4. When turning on the primary channel, the K factor should be less than 0.25.

Clean Water Needs
Analysis of projected clean water needs to be carried out based on the Real Demand Survey (RDS) and customer data from the Regional Drinking Water Company of East Lombok Regency in 5 subdistricts of 98,5 lt/person/day and following the clean water requirement standard for sub-district classification using a standard requirement of 100 l/day/person.The criteria used in preparing water needs in the service plan area are: 1. Calculation of drinking water supply system planning until 2030 with a service level of up to 80% of the total population.2. Water loss rate of 20%.3. The planning area for this activity includes service areas in 5 sub-districts in the south coast region.4. One SR serves 5 people/people 5. Water service: 100 lt per person per day 6.Non-domestic water needs: 20% of domestic water needs for each sub-district.7. Max day factor: 1.10 8. Peak hour factor: 1.5 for each sub-district.
The projected water needs in the service areas in the 5 (five) sub-districts in the plan year are as follows: The need for clean water in 5 (five) sub-districts or planned service areas, based on Table 3 above, is 150 l/s in the planning year and a maximum of 207,75 l/s in the projection year.

Water Requirements of Irrigation
Diversion water requirements are calculated by accounting for water losses in the fields and during transportation at the tertiary, secondary, and main canal levels.This is equivalent to considering the overall irrigation efficiency.Based on Table 4 above, the maximum irrigation water requirement for the Penyonggok Irrigation Area is 320 lt/sec with an average of 50 lt/sec.

Availability of Water
The FJ-Method is used to determine inflow potential in irrigation areas.The equipment used for measuring water flow, known as the FJ-Mock, was calibrated at the nearest weir location within the study area.The location was chosen because it had similar conditions, especially the type of soil, and was not disturbed by water withdrawals upstream.
FJ Mock Method analysis is carried out by adjusting or verifying soil parameters, by inputting rainfall data so that the reliable discharge amount is obtained which is used as a reference in determining planting patterns.
Water availability for a reliable discharge is estimated based on the discharge at Q-80% at each weir during a dry year, Q-50% at each weir during a normal year, and Q-20% at each weir during wet years.On the other hand, water availability for biota or eco-systems is estimated based on the discharge at Q-95% at each weir.

Balance of Water
The water balance analysis is evaluated based on the K-factor, which is the comparison between the available discharge and irrigation demand discharge.The K-factor is categorized into four types: continuous supply (K-factor = 0.75 -1.00), water rotation in tertiary channels (K-factor = 0.50 -0.75), water turnover in secondary channels (K-factor = 0.25 -0.50), and water turnover in main channels (Kfactor < 0.25).These criteria are used to analyze the water balance and determine the water supply in different channels.
The calculation of the water balance includes two conditions, the existing state before raw water is used, and the planned state after raw water is used.According to Table 5, the current and planned conditions for extracting raw water from these two sources result in a balanced water condition..In the Aikmampat sub-watershed, FK min decreased from 40% to 25%.The decrease in the K-factor occurred but was still within 1 FK class.This means that if the K-factor is less than 0.25, irrigation water regulation is in rotational conditions in the main canal based on water balance analysis criteria.

Conclusion
After analyzing the results of the study, we can draw several conclusions: 1) The need for clean water on the southern part of Lombok Island based on the level of service for 5 sub-districts is 151.90 l/sec, with the addition of 14,464 house connections.
2) The water balance in the Aikmampat Sub-watershed (Lingkung surface water source) has seen a decrease in the minimum FK (Reliability Factor) from the existing condition of 40% after being used for clean water needs to 25% (plan condition).This decrease is still within the threshold limit because it is still included in the same interval (range).It is necessary to regulate the water rotation in the main canal, especially in June and July, while during the rest of the time, the water supply status is continuous with 100% FK, so there is no need to rotate the water.3) In handling the drought disaster on Southern Lombok Island, based on current water availability, it is necessary to identify raw water sources.

Table 1 .
Clean Water Planning Criteria.

Table 2 .
Coefficient of Rice and Secondary Crops (Kc).

Table 3 .
Clean Water Needs.

Table 5 . K-Factor in the Aikmampat Sub Watershed
*Source: Analysis Results, 2023