Maximum Flow and Maximum Specific Flow in a Small Catchment Affected by an Extreme Rainfall Near Cherrapunjee in Northeast India

Abstract

Hourly rainfall data collected in the Maw-Ki-Syiem experimental catchment (area: 0.22 km2) during the period 1999–2009 and the application of hydrological models (SCS-CN and GIUH – previously calibrated and verified) allowed for the analysis of the hydrological response of the catchment, located in an extremely humid monsoonal climate. Due to a lack of detailed hydrological data, this area has rarely been investigated. Its hydrological response was investigated in relation to different types of rainfall, recorded in pre-monsoon, monsoon and post-monsoon seasons in 2002 and 2005. Hydrographs revealed rapid response of the catchment to rainfall. The rising limb and recession limb were very steep and coincided with hourly rainfall patterns. The observed hydrological response consisted of maximum flow of less than 2.5 m3 s−1 and a maximum specific flow of less than 11 m3 s−1 km−2 for rainfall of less than 20 mm h−1. Precipitation higher than 80 mm h−1 resulted with a maximum flow peak higher than 20 m3 s−1 and maximum specific flow exceeding 90 m3 s−1 km−2. These high flow peaks occurred in pre-monsoon and monsoon seasons but not in the post-monsoon season. Maximum specific flow in the Maw-Ki-Syiem experimental catchment is one of the highest recorded values in the world. Relationships such as rainfall intensity versus maximum flow and rainfall intensity versus maximum specific flow were evaluated in order to support the estimation of maximum flow and maximum specific flow on the basis of rainfall data (easily accessible for this region) for small catchments near the town of Cherrapunjee.