The rainfall-runoff model is commonly used in flood discharge computation. One of the most frequently employed methods to estimate the flood discharge in the ungauged basin is NRCS-CN. This study is aimed to determine the CN value with/without soil drainage capacity from the soil information in SPT Indonesia. The location used is Pataruman watershed by calibrating the simulation discharge results with the observed discharge. Soil conditions in the Pataruman watershed show that the soil texture has a fine texture (HSG D), a slightly fine texture (HSG C), and a slightly coarse texture (HSG A). The average composite CN in the Pataruman watershed without soil drainage capacity was 85.58 while soil drainage capacity was 81.01. The results of the analysis show that with/without taking into account the soil drainage capacity in the Pataruman watershed there is no significant difference in discharge with a relation coefficient of 0.734 (without soil drainage capacity) and 0.732 (with soil drainage capacity). CN calculations with/without soil drainage capacity are recommended for small watersheds.

Hydrologic Soil Group (HSG) for each region is different depending on soil conditions. It is one of the key elements in the NRCS-CN determination to account for the rain-runoff relationship. But unfortunately in Indonesia there is no map of HSG. Adidarma (2013) has conducted the research about HSG determination by using hydrogeology map. However, the map has a long process of pedotransfer and HSG parameter approach is still generally and qualitative. Furthermore, Ramadan (2017) has done research of HSG determination with HWSD map; the map is a global map which depth of information type of soil is less profound. Related to those problems, the researcher will conduct the determination of HSG in accordance with the condition of land in Indonesia by using Land Map Unit (SPT) Indonesia. HSG will be overlay with the transparent of land in Pataruman Water Catchment Area (WCA) until obtained the value of NRCS-CN and then the discharge plan will be calculated and will be calibrated with debit recording in Bendung Pataruman.