# Integrated Hydrological Analysis of Little Akaki Watershed Using SWAT-MODFLOW, Ethiopia
## 1 Introduction  
Groundwater is one of the main sources of fresh water to support human needs for domestic consumption and socio-economic development in Ethiopia. Sustainable use of the groundwater depends on understanding of the groundwater resources dynamics and its relationship with the other hydrological cycle components [1, 2]. Most of the groundwater comes from rainfall that infiltrates down from the land surface. Infiltration of rainfall through the soil unsaturated zone is the source of water to the water table, groundwater recharge. The distribution of precipitation, which is the source of almost all freshwater in the hydrologic cycle is highly variable. Likewise, evaporation and transpiration rates differ significantly according to climatic conditions. This determines the recharge distribution, and the groundwater recharge-discharge dynamics, in addition to the hydrogeological feature of the aquifer [3, 4].  
Today, to sustainably manage the water resources, the consideration of groundwater and surface water as an interconnected and single resource has been increasing all over the world due to the increasing sustainability and environmental concerns [5]. The scientific concepts and aspects about the interaction of groundwater and surface water and the necessity of dealing with it in a unified way are widely addressed by USGS [6].  
In such an interconnected water resources network, both surface water and groundwater resources need to be managed conjunctively to satisfy the current demand withoutcompromising its sustainability for the future. To do that, a physically-based distributed hydrological models handling both the surface and groundwater hydrological processes can be used to estimate water availability under present and forthcoming conditions and to manage suitable integrated water management policies [7; 8; 9].  
The central Ethiopia is the place where large number of populations lives (including the capital city of the country, Addis Ababa), and large number of industries are active. According to [PERSON] [9], the groundwater contribution to the surface water is high in the central Ethiopia, mostly in the Awash basin because of the high groundwater recharge contribution in the central highlands. The water use in the area are both from surface and groundwater sources. Groundwater contributes for more than 25% of the water supply for the capital city, Addis Ababa [10; 11]. Due to the alarmingly increasing population of the capital city and the nearby cities, the Addis Ababa Water Supply and Sewerage Authority (AAWSSA) is expanding additional groundwater sources as sources of water supply for the city. In addition, significant amounts of groundwater are pumped by private industries, institutions and individuals without necessary scientific support.  
To sustainably use and manage the groundwater resources in the area, spatial distribution, and amount of groundwater recharge, the mechanism of groundwater flow, occurrence, the interactions of groundwater with the river, and assessing the response of the system to different abstraction are the important issues to be addressed. These could be done with a reliable surface and groundwater hydrological model simulations, which also depend on thorough calibration and testing with the availability of quality hydro-climatic data [12].  
As groundwater is vital to meet the growing water demand of population, dependable estimation of groundwater recharge is fundamental for the evaluation of the groundwater resources potential [3; 13; 14]. Since directly measuring the groundwater recharge like that of precipitation or streamflow is not possible, it needs to be estimated by indirect methods. In this study, the water balance method of groundwater recharge estimation is followed to estimate the catchment scale groundwater recharge of the Little Akaki watershed using the Soil and Water Assessment Tool (SWAT) model.