ZONATION AND ANALYSIS OF DRAINAGE NETWORK CAPACITY FOR BETTER FLOOD CONTROL IN THE UNUS DRAINAGE SYSTEM, MATARAM CITY Agustono Setiawan1*, Lalu Wirahman W.1, Bambang Harianto1, IDG. Jaya Negara1, Zaedar Gazalba1 1University of Mataram, Jln. Majapahit No. 62 Mataram 83125, Indonesia *Corresponding Author: agustonos@unram.ac.id Abstract. The Unus Drainage System (UDS) is one of the drainage systems in the city of Mataram. Nowdays, this catchment area in the UDS has a fairly large and rapid change in land use, from agricultural land to housing, building shops, offices and other buildings, so causing floods in several area. New construction and maintenance of drainage channels have been carried out by several agencies, both the City, Provincial, and Central Government, but the development are still partial or not comprehensive, so that many inundation problems become moved to other place and not resolved properly. For this reason, it is necessary to do zonation of the drainage network and its catchment area in order to facilitate the arrangement of drainage network. The objectives of this study are to find out the drainage network and catchment area of each drainage channel, so that the mapping can be made, and to evaluate the drainage channels capacity or the ability of the drainage channels to accommodate runoff. The conclusions of research are the results of mapping or zonation of the UDS are divided into 20 Primary Drainage Blocks in the Right UDS and 10 Primary Drainage Blocks in the Left UDS, the capacity evaluation of the existing drainage channel in this system is that most primary channels are still able to accommodate flood discharge, except the Sekarbela, Asrama Gebang, and Abian Tubuh Mayura primary channel. With zonation and evaluation the capacity of this drainage channel, planning for the development and maintenance of drainage system can be integrated and comprehensive, so that flood control can be better in accordance with its priorities. Keywords: zonation, drainage, flood 1. Introduction Mataram City as the capital of the Province of West Nusa Tenggara (NTB), is the center of government activities in the NTB Province. With the function of Mataram City, it encouraged migration from the towns and villages around it to move to the Mataram City, so that there was an quite high increase in urban population and resulted in rapid development of the city. The development and construction of the city led to change of land use, from agricultural land or green land to residential land, roads, economic facilities and other buildings. One of the consequences is to increasing surface runoff and cause inundation in several places of the Mataram City, because land use changing is not balanced with the arrangement and construction of city drainage system which is an integrated or comprehensive. Inundation or flood problems have result the discomfort area, dirty environment, the emergence of various diseases and other adverse effects. There are five rivers flow in the Mataram city, namely the Meninting River, the Jangkok River, the Ancar River, the Mapak River and the Unus River, so that the rainfall in Mataram becomes surface runoff that has flows to the five rivers, therefore the drainage system in Mataram is divided into five drainage systems. namely Meninting, Jangkok, Ancar, Mapak and Unus drainage systems. The catchment area of Unus Drainage System (UDS) has a quite large and rapid changing of land use, from agricultural land to housing, shop buildings, offices and other buildings. The UDS is located in the southern part of the Mataram City, on the right and left of the Unus River, stretching from east to west following the Unus River basin. Inundation or flood problems that often occured in the UDS are around the Mandalika bus station (Kel. Bertais), Brawijaya Street (Kel. Cakranegara Selatan), MGM Supermarket Complex (Kel. Cakranegara Timur), Sweta Complex (Kel. Turida), Kel. Babakan, Kel. Abian Tubuh, Kel. Dasan Cermen, Kel. Pagutan, Kel. Pagesangan, Kel. Jempong Baru, Kel. Karang Pule, and Tanjungkarang Complex (Kel. Tanjungkarang). The condition of the some drainage channels in the UDS is still in good condition, but many channels are not functioning properly. New construction, repair and maintenance of drainage channels have been carried out by several agencies, both the City Government, the Provincial Government and the Central Government, but the development and repairs are still partial or not comprehensive, so many inundation problems have moved to other locations and not resolved properly. Due this reason, it is necessary to study about "Zonation and Analysis of Drainage Networks Capacity for the Better Floods Control in the Unus Drainage System, Mataram City". The objectives of this study are to know the drainage network (location and dimensions), flow pattern and catchment area of each drainage channels, so that a mapping or zonation can be made in the UDS. In addition, the study will to evaluate the capacity drainage channels that the channels are able to accommodate surface runoff discharge with the current land use in the UDS. With the two objectives above, the construction and maintenance planning of UDS can be more integrated and comprehensive, so that floods or inundations control can be better with directed thoroughly according to its priorities. George Xian et al. [1] results are urbanization has transformed natural landscapes into anthropogenic impervious surfaces. Urban land use has become a major driving force for land cover and land use change in the Tampa Bay watershed of west-central Florida. This study investigates urban land use change and its impact on the watershed. Land use classifications and urban drainage network are impact to urban floods [2], urban flood studies have linked the severity of flooding to the percent imperviousness or land use classifications of a watershed, but relatively little attention has been given to the impact of urban drainage networks on hydrologic response. The drainage network, which can include storm pipes, surface channels, street gutters, and stormwater management ponds, is examined in the Dead Run watershed. And Ningrui Du et al. [3] results that urban expansion has had a significant impact on Wuhan's surface water bodies and their riparian zones. The reduction, disappearance and pollution of surface water may contribute to the undervaluation of water bodies, thereby increasing the likelihood of further impacts taking place. An integrative and proactive land use planning and management system at regional strategic level and local action level is considered to be essential if surface water systems are to be conserved and improved. Increased recognition of their societal and ecological value should be reflected in more detailed attention to the spatial requirements of water bodies and riparian areas in urban planning policies. AbbasBenzerra et al. [4] develop a methodology for assessing the urban drainage system sustainability. The method mainly consists of two approaches. The first approach facilitates the identification of criteria and indicators. The second approach assesses the performance of the Urban Drainage System. This methodology provides a set of indicators for operational applications in Urban Drainage System. 2. Drainage System Drainage is one of the basic facilities designed as a system to meet community needs and is an important component in urban planning (especially infrastructure planning). Drainage means to drain, dispose of, or divert water. In general, drainage can be defined as a technical action to reduce excess water, both from rainwater, seepage, or excess irrigation from an area or land, so that the function of the area or land is not disturbed [5]. According to RJ Kodoatie [6], the drainage system generally consists of receiver channels (interceptor drain), collecting channels (collector drain), conveyor channels (conveyor drain), primary channels (main drain), and a receiving water body (receiving waters). The drainage network system in the city area is divided into two parts RJ Kodoatie [6], namely: Major Drainage System The major drainage system is a channel system that conveys water from a catchment area to a river. In general, the major drainage system is also referred to as the main sewer system (main drainage) or primary drainage. This network system accommodates large and wide-scale flows such as primary drainage channels. This macro drainage plan is used with 5 and 10 years return period and detailed topographic measurements are absolutely necessary in planning this drainage system. Micro Drainage System Micro drainage system is a drainage system that complementary system in the micro drainage system, such as channel along the side of the road, channel around the building, culverts, city drainage channels etc. In general, micro drainage is planned with 2.5 or 10 years return period. According to R. J. Kodoatie [6], the problem of urban drainage is not a simple matter. Many influencing factors and careful consideration in planning include: Increased Debit Increased water discharge occurs because it increases the intensity of rain that occurs in the catchment area. So that the drainage can not be able to accommodate the discharge that occurs, water overflows and there is inundation or even flooding can occur. Environmental Arrangement The development of new housing, especially by developers, was not followed by adequate drainage arrangements. Residential buildings that narrow the dimensions of the channel. Contour shape changes for settlement development have partly changed the direction of flow which has an impact on the gap between the drainage arrangement plan and reality. Changes in Land Use In former rice fields, the existing drainage channels are irrigation channels. This change in function is not followed by channel design changes. Changes in land use that are not in accordance with planning, especially in riverbank areas and channeling bodies for settlements. Almost all areas are small building areas and recharge areas. Some existing channels are still natural channels even though the previously empty land has become a dense settlement. Channel Capacity The existing channels are less able to accommodate rainwater discharge even though the land for channel development is non-technical (normalization). Function Misuse of the channel function itself, some channels are still mixed used for drainage and sewerage. 2.1 Drainage Capacity Analysis Hydrological analysis is the initial stage of planning to estimate the amount of peak discharge in the area. Rainfall data is very important data in hydrological analysis, because rainfall data is needed in the design of the discharge and to determine the dimensions of the drainage channel. Calculation of peak discharge is obtained from processing daily rainfall data. To get peak discharge, the Rational Method is used, watershed with a small size, which is less than 300 ha. Mathematical equations is expressed in Equation 1 [5]. Q = 0.002778 CIA (1) Where: Q = Peak discharge (m³ / second) C = Runoff coefficient I = Rainfall intensity (mm / hour). A = Area of ​​catchment area (ha). The drainage channel capacity is the ability of the existing drainage channel to accommodate or drain the amount of runoff discharge. The capacity of the existing drainage channel is calculated to find out whether the drainage channel is still able to accommodate the flood discharge or not (at the channel evaluation stage). To find out the drainage channel capacity, a field survey is needed. Field survey to obtain channel dimension data which includes channel length, channel depth, sedimentation depth in the channel, width of the upper and lower channels and the shape and material of the channel, and the slope of the channel. So according to Suripin [5] the equations of drainage channel capacity used are as follows: Q = A.v (2) A = b.h .(3) b = 2.h or h = b / 2 (4) P = b + 2h (5) R = A / P (6) (7) (Suripin, 2007: 147) [5] Where : Q : Debit (m³ / s) A : Wet channel area (m²) v : velocity (m / s) b : Channel base width (m) h : Normal water height on channel (m) S : Channel slope n : Manning coefficient The purpose of drainage channel evaluating is to find out whether the drainage channel is still able to accommodate the peak discharge with a 2 years and 5 years return period, by comparing the channel capacity discharge that calculated based on existing conditions with peak discharge which is calculated based on the amount of rainfall land use and topography of the catchment area. If the discharge of channel capacity is greater than the peak discharge, it is concluded that the drainage channel is still able to accommodate flood discharge, whereas if the discharge Q channel capacity is smaller than the peak discharge, it is concluded that the water in the channel will overflow. 3. Methodology The research has carried out in the Unus Drainage System (UDS) in the Mataram City. UDS located on the right and left of the Unus River which flows towards the Unus River. This research is planned with several stages so that the expected goals can be achieved, while the research stages are as follows: To collect secondary data, which consists of topographic maps and study area land use maps, as well as maximum daily rainfall data To survey and observation in UDS location, to find out the existing drainage network, flow pattern and catchment area, and the dimensions of the existing drainage channel. To make zonation drainage networks To determine the capacity of each existing drainage channel To determine surface runoff discharge in each catchment area To evaluate the drainage channel, whether its capacity can still accommodate surface runoff water discharge To analyze the improvement of integrated and comprehensive drainage networks Figure 1. Research Flow Chart 4. Results and Discussion 4.1 Data Collection Data collected in this study consisted of rainfall data, topographic maps and land use maps. Rainfall data is very important data in hydrological analysis, because rainfall data is needed in the design of the discharge and to determine the dimensions of the drainage channel. Calculation of flood discharge is obtained from processing daily rainfall data. To get flood discharge, the Rational Method is used. In this study, daily rainfall data from 2 (two) rainfall stations were used, namely Bertais and Monjok rainfall stations. The rainfall data obtained is 10 years of daily rainfall data, from 2008 to 2017. The rainfall data is used the maximum daily rainfall. The calculation results of the maximum daily rainfall average for two rainfall stations can be seen in Table 1. Table 1. Maximum Daily Rainfall (mm)  Year Maximum Daily Rainfall (mm) 2008 43.00 2009 186.00 2010 104.50 2011 48.00 2012 64.50 2013 48.00 2014 57.00 2015 63.50 2016 115.00 2017 76.50 Source: Calculation Result Topographic map is used to determine the flow pattern, catchment area and determine the elevation and slope of the channel. Topographic maps used in the research were obtained from the Mataram City Government. Land use map is needed to determine the runoff coefficient and flood discharge. The land use map is obtained from satellite image data (Google Earth). 4.2 Flow Pattern and Catchment Area The flow pattern is a series of rainfall flows direction that fall on the land and flow naturally (gravitation) to a river, sea or lake within the catchment area. Flow patterns are determined based on topographic maps and surveys to locations. This flow pattern is used to determine the zonation (mapping) of drainage networks. The catchment area is a part of the land which rainfall fall on the land and flow to a drainage channel. The catchment area is determined based on topographic maps and surveys to the location. This catchment area used to determine flood discharge and also to determine the zonation (mapping) of drainage networks. 4.3 Zonation of Unus Drainage System The UDS is a collection of drainage networks that flows into the Unus River. The UDS consists of two systems, namely the Right Unus Drainage System (northern of the Unus River) and the Left Unus Drainage System (southern of the Unus River). The Right Unus Drainage System is a collection of drainage networks that flow into the right bank of Unus River, while the Left Unus Drainage System is a collection of drainage networks that flow into the left bank of Unus River. The Right and Left Unus Drainage System consists of several Primary Drainage Network Blocks (Primary Blocks), which each primary channel flow into the Unus River. 4.3.1 Unus Right Drainage System The Right Unus Drainage System is located in the right bank (northern) of Unus River, and extends or runs from east to west, starting from the Bertais Village (Sandubaya Sub District) to Tanjung Karang Village (Sekarbela Sub District). The drainage network in the Right Unus System is spread over 4 (four) sub-districts, namely Sandubaya, central part of Cakranegara, Northern of Mataram and Northern of Sekarbela. Based on the survey, determining of the flow pattern and catchment area for existing conditions of the drainage network, the Right Unus Drainage System is divided into 20 (twenty) Primary Drainage Network Blocks, each Primary Block has a Primary Channel. Primary Blocks of drainage networks in the Right Unus Drainage System can be seen in Table 2. 4.3.2. Left Unus Drainage System Left Unus Drainage System is a drainage network located in the river basin of Unus on the left or southern, located lengthwise from east to west, starting from Babakan Village (Cakranegara) to Tanjung Karang Village (Sekarbela). The main drainage / main channel on the Unus Kiri network system flows into the left bank of Unus River. The Left Unus Drainage System is spread over 3 (three) sub-districts, namely the southern part of Sekarbela Sub District, the southern part of Mataram Sub District and the western part of Sandubaya Sub District. The drainage network in this system also consists of irrigation networks which also function as drainage channels, namely the Left Pesongoran Irrigation Network which already existed before the area developed into a residential area. The Left Pesongoran Irrigation Network is sourced in Pesongoran Weir (East Pagutan). Based on the survey of existing conditions, the Left Unus Drainage System is divided into 10 (ten) Primary Drainage Network Blocks. The Primary Block in the Unus Kiri drainage system can be seen in Table 3. Table 2. The Primary Block of Right Unus Drainage System Primary Block Name of Primary Block Name of Main Drainage Channel Village Region of Catchment Area UKa 1 Muara Unus Kanan Muara Unus Kanan Channel Kel. Tanjung Karang UKa 2 Tanjung Karang Tanjung Karang Channel Kel. Tanjung Karang, Tanjung Karang Permai, Kekalik Jaya, Kr. Pule, Punia UKa 3 S Salahuddin Batu Dawe S Salahuddin Batu Dawe Channel Kel. Tanjung Karang UKa 4 Panjitilar Selatan Panjitilar Selatan Channel Kel. Tanjung Karang, Kr. Pule UKa 5 Swasembada Swasembada-Karang Pule Channel Kel. Karang Pule UKa 6 Sekarbela Sekarbela Channel Kel. Karang Pule, Pagesangan Barat, Pagesangan, Pagesangan Timur, Punia UKa 7 Pagesangan Pagesangan Channel Pagesangan UKa 8 AR. Hakim Selatan AR. Hakim Selatan Channel Kel. Pagesangan Timur, Mataram Timur UKa 9 Taman Baru Taman Baru Channel Kel. Pagesangan Timur UKa 10 Perumahan Cristal Sayung Perumahan Cristal Sayung Channel Channel Kel. Pagesangan Timur, Mataram Timur UKa 11 Bung Karno Sayung Bung Karno Sayung Channel Kel. Pagesangan Timur, Cilinaya UKa 12 Sriwijaya Utara Sriwijaya Utara Channel Kel. Cilinaya, Pagesangan Timur, Sapta Marga UKa 13 Karang Pule Pagesangan Irigasi Pesongoran Kanan Channel Kel. Karang Pule, Pagesangan Barat, Pagesangan, Pagesangan Timur UKa 14 Asrama Gebang Asrama Gebang Selatan Channel Asrama Gebang Utara Channel Kel. Pagesangan Timur Kel. Pagesangan Timur UKa 15 Irigasi Cakra Gebang Irigasi Cakra Gebang Channel Kel. Cakranegra Barat, Cilinya, Sapta Marga, Pagesangan Timur UKa 16 Abian Tubuh Sapta Marga Abian Tubuh Sapta Marga Channel Kel. Sapta Marga, Abian Tubuh Baru UKa 17 Abian Tubuh-Mayura Abian Tubuh-Mayura Channel Kel. Mayura, Cakranegara Timur, Cakranegara Selatan, Cakranegara Selatan Baru, Abian Tubuh Baru, Babakan UKa 18 Babakan Babakan Timur Channel Kel. Babakan UKa 19 BTN Sweta BTN Sweta Channel Kel. Babakan, Turida, Bertais UKa 20 Turida Babakan Turida Timur Channel Kel. Babakan, Turida, Mandalika, Bertais Kel. Babakan, Turida Timur Source: Survey results Figure 2. The Primary Block of Right Unus Drainage System  (Source: Survey results) Table 3. Primary Blocks in Left Unus Drainage System Primary Block Name of Primary Block Name of Main Drainage Channel Village Region of Catchment Area UKi 1 Muara Unus Kiri Loang Baloq Channel Tanjung Karang UKi 2 Batu Ringgit Batu Ringgit Channel Tanjung Karang, Karangpule UKi 3 Pagesangan Pepabri Pagesangan Pepabri Channel Pagesangan, Karangpule UKi 4 Pagesangan Unmuh Pagesangan Unmuh Channel Pagesangan UKi 5 Pesongoran Kiri Irigasi Pesongoran Kiri Channel Tanjung Karang, Pagesangan, Karangpule, Pagutan Barat, Pagutan Timur UKi 6 Batu Bolong (Pagutan Permai) Batu Bolong Channel Pagutan Barat UKi 7 Bung Karno Bung Karno Barat Channel Pagutan Barat UKi 8 Pagutan Timur Pagutan Timur Channel Pagutan Timur UKi 9 AA Gde Ngurah AA Gde Ngurah Channel Dasan Cermen,Babakan UKi 10 Babakan Babakan Kebon Channel Babakan Source: Survey results Figure 3. The Primary Block of Left Unus Drainage System Source: Survey results 4.4 Capacity of Existing Drainage Channels The drainage channel capacity is the ability of the existing drainage channel to accommodate or drain the amount of runoff discharge. The capacity of the existing drainage channel is calculated to find out whether the drainage channel is still able to accommodate the flood discharge or not (at the channel evaluation stage). To find out the drainage channel capacity, a field survey is needed. Field survey to obtain channel dimension data which includes channel length, channel depth, sedimentation depth in the channel, width of the upper and lower channels and the shape and material of the channel, and the slope of the channel. Calculation of drainage channel capacity of Unus Drainage System is presented in the analysis/evaluation of each Primary Block. 4.5 Surface Runoff Discharge Surface runoff discharge is calculated based on the amount of rainfall, topography and land use. Calculation of surface runoff starts with calculation of design rainfall, then the statistical parameters are calculated to select the suitable. The result of frequency distribution analysis is selected the Log Pearson Type III distribution. The amount of rainfall design with Log Pearson Type III distribution can be seen in Table 4. Table 4. The design rainfall with Log Pearson Type III distribution  No Return Periode (Year) G Coeffisient Design Rainfall (mm) 1 2 0.202 77.23 2 5 0.727 91.32 3 10 1.342 111.16 Source: Calculation results The surface runoff discharge is calculated using the Rational Method, calculation of surface runoff discharge is shown on the evaluation table of the drainage channel. 4.5 Evaluation of Drainage Channel Evaluation of drainage channels in the UDS is carried out on each Primary Block which has been arranged at the zonation or mapping stage. The purpose of drainage channel evaluating is to find out whether the drainage channel is still able to accommodate the flood discharge with a 2 years and 5 years return period, by comparing the channel capacity discharge that calculated based on existing conditions with flood discharge which is calculated based on the amount of rainfall land use and topography of the catchment area. If the discharge of channel capacity is greater than the flood discharge, it is concluded that the drainage channel is still able to accommodate flood discharge, whereas if the discharge Q channel capacity is smaller than the flood discharge, it is concluded that the water in the channel will overflow. The results of the calculation of the drainage channel evaluation can be seen in Table 5 and Table 6. The evaluation of the capacity or capability of the existing drainage channel in the Unus Drainage System is that most primary channels are still able to accommodate flood discharge with a 5 year return period, except the Sekarbela primary channel (UKa 6), Asrama Gebang (UKa 14), and Abian Tubuh Mayura (UKa 17). While secondary channels that are unable to accommodate 5-year return flood discharge are secondary channels in Primary Blocks of Tanjung Karang (UKa 2), Abian Tubuh Mayura (UKa 17), Babida Turida (UKa 20) and Batu Bolong (UKi 6). Table 5. The Evaluation of Primary Channel in Right Unus Drainage System Primary Block Name of Channel  Dimension of Channel Channel Slope Q 2yr (m3/s) Q 5yr (m3/s) Q Cap. (m3/s) Evaluation ba (m) bb (m) ha (m) hs (m) Q 2yr Q 5yr U Ka 1 Sal. Muara Unus Kanan 0.00 0.70 0.60 0.15 0.011 0.06 0.07 0.63 accommodate accommodate U Ka 2 Sal. Tanjung Karang 5.90 5.30 1.00 0.20 0.002 3.82 5.83 8.98 accommodate accommodate U Ka 3 Sal. S. Salahudin Utara 0.90 0.70 0.65 0.05 0.003 0.31 0.37 0.43 accommodate accommodate U Ka 4 Sal. Panji Tilar 3.10 2.70 1.60 0.10 0.005 0.23 0.28 11.47 accommodate accommodate U Ka 5 Sal. Swasembada Kr. Pule 0.00 1.45 0.85 0.20 0.021 0.38 0.45 3.80 accommodate accommodate U Ka 6 Sal. Sekarbela 0.00 3.20 1.00 0.30 0.002 3.65 4.32 3.88 accommodate overflow U Ka 7 Sal. Pagesangan Barat 0.00 1.00 0.20 0.30 0.002 0.07 0.08 0.10 accommodate accommodate U Ka 8 Sal. Ar. Hakim Selatan   1.90 1.10 0.25 0.012 0.96 1.14 5.75 accommodate accommodate U Ka 9 Saluran Taman Baru 0.00 1.70 0.85 0.00 0.004 1.21 1.44 1.94 accommodate accommodate U Ka 10 Sal. Perumahan Cristal Sayung 0.00 1.00 0.75 0.05 0.011 0.18 0.22 1.39 accommodate accommodate U Ka 11 Sal. Sayung 0.00 5.50 3.50 0.50 0.001 1.21 1.43 38.59 accommodate accommodate U Ka 12 Sal. Sriwijaya Kura 0.00 0.65 0.50 0.20 0.026 0.18 0.21 0.71 accommodate accommodate U Ka 13 Sal. Irigasi Pesongoran Kanan 3.00 2.40 0.90 0.60 0.004 0.78 0.92 4.24 accommodate accommodate U Ka 14 Sal. Asrama Gebang Selatan 1.05 0.85 0.80 0.20 0.014 1.36 1.60 1.60 accommodate overflow U Ka 15 Sal. Irigasi Gebang Cakra 2.50 2.30 0.90 0.10 0.003 2.25 2.67 3.28 accommodate accommodate U Ka 16 Sal. Abian Tubuh Barat 2 0.00 0.50 0.45 0.05 0.005 0.14 0.17 0.19 accommodate accommodate U Ka 17 Sal. Abian Tubuh-Mayura 3.30 3.20 1.50 0.20 0.003 7.87 9.30 8.82 accommodate overflow U Ka 18 Sal. Babakan Timur 1.80 1.40 1.40 0.05 0.005 0.73 0.87 4.54 accommodate accommodate U Ka 19 Sal. BTN Sweta 2 0.00 1.90 1.00 0.20 0.008 0.56 0.67 4.28 accommodate accommodate U Ka 20 Sal. Turida Timur 0.00 1.80 0.80 0.25 0.022 0.28 0.38 4.79 accommodate accommodate Source: calculation results Table 6. The Evaluation of Primary Channel in Left Unus Drainage System Primary Block Name of Channel  Dimension of Channel Channel Slope Q 2yr (m3/s) Q 5yr (m3/s) Q Cap. (m3/s) Evaluation ba (m) bb (m) ha (m) hs (m) Q 2yr Q 5yr U Ki 1 Loang Baloq 1.70 1.70 1.20 0.20 0.003 0.15 0.17 2.73 accommodate accommodate U Ki 3 Pagesangan Pepabri 0.70 0.70 0.50 0.20 0.013 0.43 0.49 0.56 accommodate accommodate U Ki 4 Pagesangan Unmuh 0.60 0.60 0.65 0.10 0.005 0.25 0.28 0.39 accommodate accommodate U Ki 5 Irigasi Pesongoran Kiri 4.20 4.20 0.90 0.25 0.003 4.89 5.47 6.05 accommodate accommodate U Ki 6 Batu Bolong 1.90 1.90 1.20 0.20 0.004 1.22 1.37 3.92 accommodate accommodate U Ki 8 Bung Karno Barat 0.70 0.70 0.90 0.10 0.009 0.19 0.21 0.75 accommodate accommodate U Ki 9 AA Gde Ngurah Timur 2.00 1.50 0.90 0.10 0.006 1.97 0.85 2.90 accommodate accommodate U Ki 10 Babakan Kebon 1 0.50 0.50 0.45 0.05 0.022 0.11 0.13 0.39 accommodate accommodate Source: calculation results 4.6 The Improvement of Drainage To improve the drainage channel that cannot accommodate the flood discharge, a number of things can be done, such as dredging / lifting sediments in the channel, or enlarging the dimensions of the channel, or diverting the flow to other systems that have a small load or nearby river, or by reducing the flood discharge to the channel by making infiltration wells, or making forests or parks in the city, or making ponds / polders. Alternative methods of drainage improvement for each location should require more in-depth study based on the location conditions. 5. Conclusion Based on the results obtained from several stages in this study, conclusions can be taken as follows: The zonation results of the UDS are divided into 20 (twenty) Primary Blocks in the Right Unus Drainage System and 10 (ten) Primary Blocks in the Left Unus Drainage System, the block distribution is based on topography, patterns flow, rain catchment area, and existing drainage channels. The capacity of the existing drainage channels in the UDS are that most primary channels are still able to accommodate flood discharge with a 5 year return period, except the primary channel of Sekarbela (UKa 6), Asrama Gebang (UKa 14), and Abian Tubuh Mayura (UKa 17). While secondary channels that are unable to accommodate the 5-year return flood discharge are secondary channels in Primary Blocks of Tanjung Karang (UKa 2), Abian Tubuh Mayura (UKa 17), Babida Turida (UKa 20) and Batu Bolong (UKi 6). By zonation and the capacity evaluation of this drainage channel, planning for the construction and maintenance of drainage networks in the UDS in the Mataram city can be integrated and comprehensive, so that flood or inundation control of can be directed thoroughly according to its priorities. According on the results of study, it can be suggested that planning for the construction and maintenance of an integrated and comprehensive drainage network is needed in the UDS, so that the constructions and improvements of drainage networks in this area are not partial, but it can be resolved properly. 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