Hydrological Modelling with HEC-HMS in Krueng Peudada Sub-Watershed Bireuen Regency

The flood that occurred in Krueng Peudada was influenced by several factors, such as watershed conditions. Heavy rains caused Krueng Peudada to overflow so that a number of villages adjacent to the river were submerged. Based on these problems, to minimize the occurrence of flooding in Krueng Peudada building, namely by carrying out occurrence of flooding in Krueng Peudada to be used to obtain peak discharge as a reference in building planning in Krueng Peudada using HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modelling System). The benefit of the research is that the resulting model can be useful as a guide in calculating flood discharge considerations. The scope of this research includes the research location at Krueng Peudada using annual maximum daily rainfall data, calculating the return period of rainfall using of Gumbel probability distribution, Normal Log, Normal, and Pearson III Log as the basis for calculating the discharge and continuing the calculation of the hours with Manonobe and ABM. The results of calculations of the Nakayasu Synthetic Unit Hydrograph Method and running from HEC-HMS found that the flow that occurred in the Krueng Peudada two sub-watershed was 2903m3/second and 2723,0 m3/second, it can be concluded that in determining watershed management the flood discharge obtainded has error as much as 6,2%. The difference in the results obtained is due to the number of sub-watersheds in the watershed based on different flows and the value of the curve number for each area of the sub-watershed.


Introduction
The Krueng Peudada River is located in Bireuen district, Aceh Province, with an area of 449,03 km 2 with a length of 37,5 km as the main river.High-intensity rains caused the Krueng Peudada River to overflow, causing a number of villages adjacent to the river to be flooded.Krueng Peudada has a slope steep at the upstream and low slope low downstream, resulting in The water flow flows at a gentle speed in the downstream area.This condition is exacerbated by the occurrence of narrowing (bottle neck) around bridge at Krueng Peudada (downstream) [1].The aim of this study is to determine the flood discharge for the 100 year return period using the HEC-HMS software and the Nakayasu Synthetic Unit Hydrograph methods.The HEC-HMS program is a computer program for calculating rain transformation and routing processes in a watershed system.The HEC-HMS model can provide a hydrological simulation of daily peak flow for calculation of the design flood discharge of a watershed [2].The Nakayasu methods was developed based on several rivers in Japan.Nakayasu method is a way to obtain a flood hydrograph design of a watershed [3].The benefit of this research is to know the magnitude of the flood discharge on the Krueng Peudada River so that it can be used for planning river control structures to prevent flooding.The calculation of the return period of rainfall uses the probability distribution test [4] and the calculation of hourly rainfall distribution uses the Mononobe method [5].The discharge calculation uses the Nakayasu methods and HEC-HMS program. .

Data Analysis
Stages and techniques of data analysis in research are as follows: 1. Secondary data collection in the form of daily rainfall data from BWS I Sumatera, and raster data in the form of location maps, 2. Determination of sub-watershed boundaries and making contour maps using raster data with ArcGIS 10.2.1 software [6].3. Determination of annual maximum daily rainfall from available rainfall data for 15 years (2001-2016).4. Calculation of statistical parameters from rainfall data samples from Pearson Log III 5. Calculation of rainfall return periods of 2, 5, 10, 25, 50, and 100 years and required frequency analysis in the form of statistical analysis of the distribution of extreme values using Pearson III logs.6. Compatibility test calculations using Chi Square and Smirnov Kolmogorov tests.7. The calculation of regional rainfall uses the results of the return period rainfall calculation.
Then proceed with the calculation of Intensity, Duration and Frequency (IDF) with Manonobe.8. Calculation of design rain intensity for hourly rain distribution using the Alternating Block Method (ABM).9. Calculation of peak rainfall discharge using the Nakayasu and HEC-HMS methods.

HEC-HMS Delineation
The Delineation using HEC-HMS is as follows: 1. On the HEC-HMS toolbar menu select file then create name and description to create a new folder.2. On the component consisting of the basin model manager or the das component to be modeled.
Select new and fill in the name and description.3. Enter DEM data, select GIS on the toolbar then select a coordinate system and select browse, then press set.4. Data component select terrain data manager.Select new, name then save. 5. Next, in view, select the map layer, click add and select icons, reaches, and subbasin.6.In GIS, select the break point manager for the brown outlet point.7. Then select the delineation element consisting of sub basin prefix, reach prefix, junctions prefix, and convert break point.8. Select the map layer to see the flow and color of the layer.

HEC-HMS Models
Hydrological modeling using HEC-HMS as follows: 1. Select the existing basin model on the HEC-HMS screen, by selecting the subbasin consisting of downstream, area, loss method, transform method.2. Fill in the initial abstraction value, curve number and impervious value in the tools loss section 3. Continue with filling in the standard lag and peaking coefficient in the transformer section.
The filling of each of these data is carried out in accordance with the data that has been calculated previously.4. The reviewed return period consisting of 2,5,10,25,50, and 100 years is filled in the meteorological manager tool.The selection of the return period is carried out via the specified hyetograph with the next subbasin selecting gage and return period, while in the component manager section selecting basin and pressing yes. 5. Furthermore, in the control specifications section, a clock control is carried out which will be reviewed in hours to get a peak discharge at the same time as the time series data [5].

Design Flood Discharge of Nakayasu
After calculating and constructing the design rain histograph with ABM, calculations and bar chart formation of the effective rain histograph are carried out.The results of the analysis of the calculation of the planned rainfall using the Log Pearson III distribution produce total hydrograph data and flood discharge return periods of 2 years, 5 years, 10 years, 25 years, 50 years and 100 years with the Nakayasu methods on the Krueng Peudada River.The total hydrograph is a hydrograph of direct runoff caused by rain as high as 25 mm, 50 mm and 55 mm, where the effective rain is part of the rain that flows directly into the river.Calculation of the planned flood discharge using the Nakayasu methods aims to determine flood discharges of 10 years, 25 years, 50 years and 100 years so that a comparison can be seen between the data calculated manually using the Nakayasu methods and also the HEC-HMS application, after which testing is carried out on the data obtained are both useful to determine the accuracy of the data.The results of calculations using the Nakayasu methods can be seen in Table 1.Based on Table 1, it can be seen that in the 2 year return period there is a peak discharge of 1130.7 m 3 /sec., the 5 year return period there is a peak discharge of 1732.8 m 3 /sec., the 10 year return period there is a peak discharge of 1191.4 m 3 /sec., a return period of 25 years has a peak discharge of 2296.2 m 3 /sec., a return period of 50 years has a peak discharge of 2513.5 m 3 /sec.and a return period of 100 years has a peak discharge of 2723.0 m 3 /sec.

Design Flood Discharge of HEC-HMS
The results of running with the HEC-HMS show the simulated peak discharge shown in Figure 2. The blue bar-shaped graph shows the amount of rain that occurs in the 100-year return period in the form of peak rain, while the red graph represents loss or lost rain.caused by infiltration in the rain in the sub-watershed area caused by rain absorbing into the soil or absorption of rain by plants.

Figure 2. Results for Run with HEC-HMS
The simulation results of the peak discharge of the Krueng Peudada watershed at the 100 year return period with the Nakayasu methods yield 2723,0 m 3 /sec., then an error test is carried out to determine the magnitude of the error rate in the comparison of the simulation results with the data sought.To perform error testing, a peak discharge is required.The peak discharge value at the 100 year repeat period using the HEC-HMS is 2903,0 m 3 /sec.The results of calculations using the Nakayasu methods can be seen in Table 2.The results of testing the value of the peak discharge error in the 100 year return period between the Nakayasu methods and the HEC-HMS program are 6.2%.

Conclusion
The results of the comparison of the peak discharge for the 100 year return period between the HEC-HMS program and the Nakayasu methods are not more than 10%, the difference in the error value is 6.2%.The results of calculations using the Nakayasu methods can be used for planning flood control structures on the Krueng Peudada river.The difference in the results obtained is due to the number of sub-watersheds in the watershed based on different streams and the curve number value for each area of the sub-watershed.