Land inventory and designation of the Kranji river riparian zone in Purwokerto city, Central Java

River banks are virtual lines of the riverbed designated as river protection boundaries. This research aimed to inventory the Kranji Riverbank’s land condition and conduct a study to determine the width of the riparian zone. The methods used were field surveys, identification of land along the 11 km river, and analysis of flood discharge designs with a return period of 10 years. The results of an inventory along the river on the river land dominated the permanent building. There are 400 building units included in the repair zone on the Kranji River. Based on the planned flood analysis results with a return period of Q10 years of 38.11 m3/s, there are 160 flood points along the river. The width of the riparian zone in urban areas is 10 meters in East Purwokerto, while outside urban areas, it is 50 meters in Baturaden District. The benefit of the results of this research is the provision of initial data for coordinating with several other agencies in efforts to implement the Kranji River border in the future.


Introduction
The river bank is a significant area both for the preservation of the river as a source of water for the community, for the preservation of the river as a vital aquatic, amphibian, and terrestrial ecosystem, and for the preservation of the river as an eco-drainage area for flood and landslide control.However, the looting of riparian land for housing, shops, offices, and other permanent facilities has been intensifying [1].
A regulation, namely PP No. 28/PRT/M/2015, establishes boundaries for rivers and lakes by issuing the Regulation on the Establishment of Rivers and Lakes Boundary Lines.Determining the river boundaries requires an in-depth study of various fields and other related aspects, such as studies of river morphology, hydrology, engineering, social, law, and others, as an integral part of the mandate of government regulation [2].
River banks in urban areas have a smaller width when compared to the width of river banks in rural areas.The most expansive river boundaries are found in rural areas, categorized into large and unkempt rivers with a river border width of 100 meters.Further in-depth study is necessary to examine these widths based on actual field conditions, considering various considerations [3].
The Kranji River riparian zone has never been studied before by the government.The use of space on the Kranji River riparian zone has indicated many violations on the side land of the river.The lack of socialization in the community has resulted in many housing developments built for decades on the banks of the Kranji River [4].
A study on handling flood-prone settlements on riverbanks was carried out in the Tondano Riverbank area by taking a case study in the Kuala Jengki settlement that if a river area is in an urban area, the width of the riverbank that must be at least 3 meters on the left and right of the river body, it is necessary to create an artificial border in the form of an embankment in every riverbank area where there is no wide border [4,5].The facts are that many obstacles become obstacles to increasing legal awareness.The main factors are the minimal awareness of building owners on river borders and the existence of economic factors for constructing buildings on river borders, making it increasingly difficult for building owners on river borders to move from the area [5,6].The study of determining river delineations in Banjarmasin considers cultural factors and activities around the river [6,7].This research posits that existing regulations can be applied by considering local cultural factors.
The research results concerning river border issues, encompassing the Cimanuk, Cinangka, and Ogan Rivers, portray a similar scenario.This result indicates that a significant portion of the river borderland features permanent structures that have been in place for over 20 years, and most of the land is already under the ownership of residents who hold Certificates of Ownership (SHM).
This study aims to determine the width of the Kranji River border in Purworejo Regency, Central Java.The study began by tracing activities on the Kranji River 11 km from the upstream of the Kranji River towards the south in the downstream part of the river.The river search aims to inventory the land on the banks of the Kranji river, which is estimated to fit into the river border width criteria.In this study, hydrological aspects, hydraulic aspects of river flow, and river morphology analysis were also undertaken, along with interviews involving individuals whose land lay within the Kranji River border area.
Land use in the Kranji River watershed is plantations/gardens with an area of 47 ha (4.25%), scrubland with an area of 3 ha (0.27%), rice fields with an area of 583 ha (52.76%), settlements have an area of 471 ha (42.62%), the field has an area of 1 ha (0.09%).In the upstream area of the Kranji River, the use of rice fields and plantations is dominant.In the middle part of the Kranji River, residential areas dominate because this section passes through urban areas.In the Kranji River's downstream area, settlements dominate, as indicated in Table 1 [8].

Rainfall Analysis
Rainfall data is part of hydrological data, which is essential for analysis in various types of planning.
The rain data collected from the results of recording a rain station can be used to predict the upcoming annual planned rainfall.Planned rainfall is an estimate of rain that will occur in a watershed.This study analyzes the annual planned rainfall using the Pearson Type III and Gumbel Log Distribution method.The method used to determine the amount of planned rainfall is usually used to analyze surface runoff and flood frequency in a watershed.The data generated using this method is from annual maximum rainfall data.Maximum rain is essential data to know because it is one of the characteristics of the factors that can cause maximum flooding in a watershed [9].

Analysis of Design Flood Discharge
The design flood discharge is the maximum discharge from a river or canal whose amount is based on/related to a certain return period.Design flood discharge is discharge with a certain return period which is expected to flow through a river or waterworks.The return period is a hypothetical time during which an event with a certain value, the planned discharge will be equaled or exceeded once within that hypothetical time period [10] [11].

Hydraulic Analysis
The hydraulic analysis in the Kranji River area used the HEC-RAS program.The HEC-RAS program is an application program that can be used to analyze and model flow in rivers; it was created by the Hydrologic Engineering Center (HEC) and is a division within the Institute for Water Resources (IWR), under the US Army Corps of Engineers (USACE).HEC-RAS is a one-dimensional permanent and non-permanent flow model in steady and unsteady flow conditions [12].HEC-RAS is an application program that integrates graphical user interface features, hydraulic analysis, data management and storage, graphics, and reporting [13].The results of running the Hec-Ras program can provide information regarding geometric flow profiles in rivers.

Determination of River Banks Based on River Morphology
River borders are further divided into flood plains, sliding plains, ecological buffer banks, and safety banks [3].Flood plain is the width between the normal river water level boundary point and the boundary point during floods (the most frequent floods).The width of the flood plain is determined by directly examining the cross-section of the river in the field.The width of the floodplain for each river section can be different depending on the transverse and longitudinal morphology of the river.Landslide bank L l ; determined based on the load distribution angle 45° (tg 45 = 1).The minimum width of the landslide bank is one and a half times the height of the cliff calculated from the foot of the cliff (1.5 H).These landslide banks are very important to understanding the existence of potential landslide areas on river banks.There are no landslide banks for rivers without cliffs, and the river banks are included in the landslide banks [13][14].

Determination of River Trough Banks
One thing that needs attention is the determination of the banks of a river trough.Riverbeds' various forms and conditions differ greatly depending on the natural situation.The following is an illustration of determining the bank of a riverbed, among others, stated: • A river with a 'V' shape lacks a floodplain.The river bank is the point of change from the cliff plane to the terraces.• A 'V-section' river typically has steep banks and few floodplains.The river bank is where the cliff changes to the river terrace.• Rivers with a flood bank on one side and a steep bank on the other are determined at an angle to the top of the river bank.• Rivers with flood banks result from land subsidence on the riverbanks and form flood banks with lower elevations, and then the riverbank is the point at the top of the cliff outside the flood bank.

Determination of Riparian Buffer Zone Width
Determination of the width of the river border is based on calculating the planned flood by looking at several studies in the field.The study is a physical study of the ecology, hydraulics, and morphology of the river based on Ministerial Regulation No. 28 of 2015, stated as follows in Table 2.

Results of Flood Hydrograph Analysis
Rainfall analysis uses the HSS Gamma 1 method unit hydrograph with rain data from 2011 to 2022.The design flood hydrograph is calculated with return periods of 10 years.The results are presented in Tables 3 and 4, as well as Figure 2.  Table 3 shows that over 12 (twelve years), the maximum daily rainfall occurred in 2017 with a value of 129.63 mm, and the minimum rainfall occurred in 2018 with a value of 90.17 mm.Meanwhile, the average value of rain is 108.63 mm.This condition shows that rainfall fluctuations over a period of 12 (two years) in the Kranji River watershed are relatively small.
The comprehensive analysis results for the design flood hydrograph, which has a return period of 10 years, are presented in Table 4, providing essential details.In this context, the data indicates that the flood peak, with a magnitude of 38.11 m³/sec, manifested itself approximately 2.9 hours into the analyzed period.Notably, this peak flood discharge value, amounting to 38.11 m³/sec, is an essential input parameter for the subsequent hydraulic analysis to be conducted employing the HecRas program.
In Figure 2, observers can witness the holistic representation of the flood hydrograph spanning a total duration of 40 hours, providing a more detailed visualization of the hydrograph's design characteristics and temporal evolution.

Results of Hydraulics Analysis with the HRC-RAS Program
The running of the Hec-Ras program is carried out in the existing conditions by including the planned Q 10 flood discharge.The results of running HEC-RAS using the steady flow method at the limit conditions of flood discharge show that runoff occurs on the banks of the Kranji River (Table 5).
Table 5 shows that from the results of the HEC-RAS Program with a 10-year return period discharge of 38.11 m 3 /second.Floods with a return period of 10 years caused flooding at 79 points on the left side of the river and 81 points on the right side.Based on government regulations, the planned flood that passes through urban areas is a 10-year planned flood, so it can be understood that the land on the Kranji River border is very prone to flooding and is dangerous for residents living in the community.
This condition aligns with the research results on the Progo River, Opak River, and Oyo River by Agus Maryono [3].A similar thing also happened to the Banjarmasin City and the Probolinggo City    Figure 4 provides a comprehensive representation of the Kranji River's trajectory, extending from its origin at point 0 km and spanning a distance of 11.0 kilometers.Field investigations have yielded significant data concerning the river borderland on both sides of the Kranji River, showcasing the presence of residential, government, and school buildings that have existed for more than three decades, emphasizing the long-standing nature of these structures.For a comprehensive insight into the land use patterns along the Kranji River, reference can be made to the meticulously presented detailed land use data in Table 6, offering thorough information regarding the utilization of land resources within this region.

3.4.Results of Morphological Analysis of the Kranji River
The morphology of the river is related to the physical condition of the river regarding the geometry, type, nature, and behavior of the river with all aspects of its changes in the dimensions of space and time, thereby involving the dynamic nature of the river and its environment which are interrelated with one another.In determining the morphology of the river, it is necessary to have river geometry data, including river width, river depth, river cross-section, location coordinates, and river bed slope [14].
Based on measurement field data, such as long-section and cross-section, the following data were obtained: In the upstream section, the width of the river is around 20 -25 m with a river depth of around 50 m, which is shaped like the letter 'V'. in the middle and downstream of the river, the average river width is 35 -50 m with a river depth of around 30 m, which resembles the letter "U".To analyze the morphology of the Kranji River, concepts from Dave Rosgen's research were used [16].River morphology, according to the definition of Dave Rosgen (1996) consists of 9 (nine) types, namely river type Aa+; Small river type A; Small river type B; Small river type C; Small river type D; Small river type DA; River type E; River type F and river type G. Figure 6 below shows the nine types mentioned above [16] The Kranji River is included in the category of periodic rivers, where the river has much water during the rainy season, while during the dry season, the water is small.Based on the origin of the incident (genetics), including the type of Subsequent River/strike valley, namely a river whose water flow follows a rock strike.Meanwhile, based on the geological structure of the river, the Kranji River is a type of Superposed River, namely a river in which the direction of the water flow, its structure, and processes are guided by the layers of rock that cover it.The Kranji River has an Entrenchment Ratio of around 1.0 to 1.4.The Entrenchment Ratio is the relationship ratio between the width of the flood flow (Wfpa) and the width of the river flow (Wbkf).The Kranji River is more appropriately included in the Small type A river group, namely the type of river with a channel slope reaching 4% to 10%, and the river flow is generally a basin with a similar water pocket.

3.5.Results of analysis of interviews with residents
The population survey was conducted on a portion of the population who live in the border area in 8 villages, including Rempoah and Kutasari villages in the Baturraden sub-district, as well as in the villages of Sumampir, Bancarkembar, Sokanegara, Kranji, Purwanegara and Kedungwuluh in East Purwokerto District.The respondents were 68 village residents, 38 men and 30 women.The tabulation results from the interviews indicated that seven respondents had elementary school education, 26 had junior high school education, and 35 had senior high school education.Forty-eight respondents were native residents of the local village, while 20 were immigrants.The homeownership status of the respondents is their own home; the remaining three respondents have rental status.Most The proposal for differentiating the width of the Kranji River border, as delineated between areas characterized as urban and those classified as outside urban zones, is a culmination of comprehensive assessments.These assessments encompass the results derived from meticulous hydrological and hydraulic analyses, elucidating the intended flood discharge characteristics of the river.Additionally, they carefully consider the intrinsic morphological attributes of the Kranji River and insights gathered from extensive interviews conducted with residents close to the Kranji River.As illustrated in Table 7, these collective considerations have formulated a framework for demarcating the river's border width.

Conclusion
Based on the results of discussions related to determining river border lines in Purwokerto City, especially on the Kranji River, as well as considering river morphology, 10-year planned flood discharge and interviews with residents, it can be concluded from this research that PUPR Ministerial Decree Number 28/PRT/M/2015 concerning river border width It is still relevant to apply to the Kranji River, where the boundary line for urban areas is 10 m from the outermost riverbed.In contrast, it is 50m from the outermost border of the riverbed for outer urban areas.The inventory results found that the amount of land and buildings estimated to fall within the Kranji River border width criteria was around 202 buildings on the left side of the river and 198 buildings on the right side of the Kranji river.Some buildings already have legal ownership status in SHM, and some do not yet have definite status or are in Petok D. Hence, categorize these buildings under the Status Quo category.Nevertheless, for field implementation, coordinate with other ranks and services, including the City Planning Service due to its relevance to urban spatial planning patterns and the Land Service concerning the legal ownership status of land and housing for residents along riverbanks.

Figure 1 .
Figure 1.Study location in the Kranji River watershed, Purwokerto Regency

Figure 2 .
Figure 2. Flood Hydrograph with a 10-year return period in the Kranji River

3. 3 .Figure 3 .
Results of Land Inventory on the Border of the Kranji RiverInventory activities on river border conditions are carried out by observing and documenting several things appropriate to the study area's conditions.Field inventory was carried out 20 km along the Kranji River on the left and right sides of the field.The current condition of the Kranji River border is mainly in settlements, gardens, fields, and rice fields.Many people's houses are included in the river borderland in several sections, as shown in Figure3.Photo documentation of the results of the inventory of the left and right lands of the Kranji River As depicted in Figure3, the identified phenomenon exhibits remarkable consistency across numerous rivers in diverse regions of Indonesia, with a particular emphasis on those traversing urban centers such as Yogyakarta, Malang, Probolinggo, and Banjarmasin[3][7][9].It is observed that, in urban areas, most residential structures situated adjacent to these rivers are typically characterized by varying land rights, some holding secure ownership through Certificates of Ownership (SHM) while others lack formalized land rights for the structures.This intricate property landscape adds a layer of IOP Publishing doi:10.1088/1755-1315/1311/1/0120308 complexity to governmental regulation efforts, owing to the intricate interplay of socio-cultural factors and the substantial compensation considerations that arise as a result.0.0 Km to 2.5 km 2.5 km to 5.0 km 5. km to 7.5 km 7.5 km to 11.0 km

Figure 4 .
Figure 4. Trase field inventory of the Kranji River from 0.0 Km to 11.0 Km

Table 2 .
Criteria for determining Riparian buffer zone width according to the Minister of Public Works and Public Housing Regulation Number 28/PRT/M/2015

Table 3 .
Regional Average Maximum Rainfall in the Kranji River

Table 4 .
Flood Hydrograph with a 10-year return period in the Kranji River

Table 5 .
Results of hydraulic analysis with the HEC-RAS Program with a 10-year flood return period

Table 7 .
Results of Analysis of the Width of the Kranji River Border namely 40, work in the private sector, 13 are traders, and the rest are sharecroppers.Respondents' knowledge of the boundaries of the Kranji River 76% of respondents said they did not understand, 14% of respondents had a little understanding of having heard of village officials, and the rest understood the boundaries.3.6 Results of the Analysis of Determining the Width of Riparian Zone Kranji River 11respondents,