No abstract

The flood phenomenon in the Krueng Jreue Sub-Watershed, Aceh Besar, Indonesia, in recent years indicates biophysical damage to the land. Floods are influenced by factors from biophysical conditions of the land and high rainfall with small river cross-sectional capacity causing water to overflow the embankment and flood low areas. This research aims to analyse the flood vulnerability level in the Krueng Jreue Sub-Watershed, Aceh Besar, Indonesia. The results showed that flood vulnerability in the research area consisted of four classes: very vulnerable, vulnerable, moderately vulnerable and somewhat vulnerable, with each area averaging a score of 43.0, 38.8, 30.0 and 21.7. Types of land use that are particularly vulnerable to flooding are rice fields with a mean total score of 43.0. The vulnerable classes are found in settlements and moorings, with a total score of 42.0 and 36.5, respectively. While open land, shrubs, grasslands, primary forests and secondary forests are quite vulnerable to flooding, with a mean total score of 32.5 each: 30.0, 30.0, 28.0 and 27.0. The main components affecting flood vulnerability are rainfall, temperature and land use, while additional components are soil infiltration and slope. Mechanised hydrological disaster mitigation can be performed through optimisation of weir, embung, rorak and check-dam. Vegetative hydrological mitigation efforts can be performed by reforestation and agroforestry systems, maps and flood prediction. Non-technically, hydrological disaster mitigation efforts can be undertaken with legal policies, law enforcement, map creation and prediction of droughts and socialisation of legislation.

The Lawe Manggamat sub-watershed has been degraded as indicated by the increasing frequency of flood events from year to year. This is related to the hampered infiltration process so that the volume of rainfall that enters the soil is getting smaller, on the other hand, the surface runoff tends to increase. This study aimed to determine the infiltration rate in the Lawe Menggamat sub -watershed, Aceh Province, Indonesia. This research uses a descriptive method (survey) which refers to the Land Map Unit (LMU) by considering the type of land use, soil type, and slope. Infiltration in the field was observed using a double-ring infiltrometer at 17 LMU. The results showed that the infiltration rate in the Lawe Menggamat sub-watershed consisted of 5 categories, namely: fast (LMU-1, LMU-8, and LMU-16), rather fast (LMU-2, LMU-3, and LMU-17), medium (LMU-6, LMU-7, and LMU-10), rather slow (LMU-4, LMU-5, LMU-9, LMU-11, and LMU-15), slow (LMU-12, LMU-13, and LMU-14)."The dominant factors affecting the infiltration rate are texture, C-organic, bulk density, soil type, and land use. Management of cover crops and organic matter, as well as forest and land rehabilitation, are expected to improve infiltration in these areas.

The phenomenon of flooding that occurs in almost all regions of the earth causes loss of property and damage to public facilities and causes the loss of many human lives. There are many reports related to the causes of flooding with various solutions offered to overcome the flood problem. However, it seems that these efforts have not been able to eliminate the flood problem. Hydrologists have widely reported various factors that are the cause of flooding with an extensive scope. Therefore, this paper is limited to discussing flooding and its problems, specifically the river flood, from the perspective of land use and soil types. Changes in land use in a watershed can cause an increase in the runoff coefficient. Likewise, different types of soil have different abilities in passing water into the ground. Open land (without land cover) tends to be prone to erosion, reducing the soil’s infiltration capacity and increased surface runoff. Increasing the runoff coefficient will increase the peak discharge in a watershed. The decrease in the river capacity due to sediment can cause a river flood. To support this argument, a rainfall-runoff model, particularly the tank model, is also discussed, taking into account the various uses and types of soil in a watershed. Efforts to anticipate the river flood are also considered for formulating flood disaster control policies in a watershed.

Climate changes are one crucial factor that influenced water availability at one location since they affected the environmental, social, and agricultural systems. The study observed the agent factors that influenced the rainfall changes at Krueng Pasee Aceh watershed, Indonesia. The method used in this research is a linear regression with a log transformation approach on predictor variables. The data used in this study consisted of rainfall, a total of rainy days, temperature, humidity, duration of irradiation, and wind speed in the period ranging from 1992 to 2020. Results showed that the agent factors had not distributed normally. The regression model produced after log transformation had met the classical assumptions and can be used to predict the rainfall at R-quare 24.61% with an RMSE value of 57.676. From all factors studied, the wind speed should be excluded. Further study is recommended to use the nonlinear method to improve the model for rainfall prediction.