Application of satellite altimetry in understanding river–wetland flow interactions of Kosi river

Abstract

Flood-plain wetlands are the seasonal water bodies formed along a river. These wetlands become active during the monsoon season, which frequently grow in size with seasonal floods and eventually dry up during the non-monsoon season. The flow interaction between flood-plain wetlands and the river sometimes vary over a very short period in response to rapid rise in the river water level due to high precipitation in its upstream catchment. Understanding the complex flow interactions between the river and its associated flood-plain wetlands with field-based measurements of wetland hydrologic characteristics is always a challenging task. To overcome these challenges, an attempt has been made to utilise Topex/Poseidon satellite altimetry-derived water levels into a hydrodynamic model (HEC-RAS) to study river and wetland flow interactions in the lower reach of the Kosi river in India. The satellite altimetry-derived water levels and Landsat satellite images on the Kosi wetlands are used to develop volume-elevation relation. HEC-RAS is setup over the study area and calibrated for different values of manning's roughness coefficient (n) for the river bank and the main channel of the river for the period of 1993-1996. Unsteady flow simulations are carried out for different monsoon seasons to simulate daily river flow interaction (inflow/outflow) between river and wetlands. Statistical analysis is performed between the altimetry-derived and the model-simulated water levels. It is found that simulated water levels are in good agreement (R 2 = 0.87, root mean square error of 0.84 m and Nash-Sutcliffe efficiency coefficient of 0.85) with altimetry-derived water levels. The analysis of simulations indicates that interactions between the wetland and the river are bidirectional with most of the flow coming out from the river during the month of August and leaving out from the wetlands during the month of September. The wetlands respond in three different ways, i.e., (i) gaining stage, (ii) wetland and river in equilibrium and (iii) loosing stage, which is reflected on water levels of the river and wetland. This study demonstrates complex interaction processes happening between the Kosi river and its surrounding wetlands.

Modelling of hydrological and environmental flow dynamics over a central Himalayan river basin through satellite altimetry and recent climate projections

“…It is used by many researchers in river water level, discharge, and estimation of river hydraulic properties (de Oliveira Campos et al ., 2001; Birkett et al ., 2002; Papa et al ., 2012; Jarihani et al ., 2013; Duan and Bastiaanssen, 2013; Dubey et al ., 2015a; 2020). The satellite altimetry has also shown great potential in calibration and validation of hydrology and hydrodynamic models in many research studies (Chander et al ., 2014; Dubey et al ., 2014; 2015b; 2021; Gupta et al ., 2015c; Chembolu et al ., 2019). The water level data were used to generate a pseudo‐rating curve for the Ayodhya and Turtipar gauge stations and this relationship was used to convert water level into discharge.…”

“…The satellite altimetry has also shown great potential in calibration and validation of hydrology and hydrodynamic models in many research studies (Chander et al, 2014;Dubey et al, 2014;2015b;Gupta et al, 2015c;Chembolu et al, 2019). The water level data were used to generate a pseudo-rating curve for the Ayodhya and Turtipar gauge stations and this relationship was used to convert water level into discharge.…”

“…However, not all watersheds are gauged specially in the South Asia; hence, increasing availability and coverage of satellite altimetry data provide a unique opportunity to study climate change impact on watersheds of different scale. Satellite altimetry presents an alternative approach for hydrological model calibration and validation in the absence of any valid ground observations (Leon et al, 2006;Calmant et al, 2008;Papa et al, 2010;Chander et al, 2014;Gupta et al, 2015b;2015c;Chembolu et al, 2019). Most of the well-maintained and updated gauge stations in South Asia are present over the main reaches of river basins.…”

Wetland Changes and Their Relation to Climate Change in the Pumqu Basin, Tibetan Plateau

“…Floodplain wetlands exist in gentle terrain areas to be able to intercept precipitation and accept floods that overflow the riverbed during the flood season. In the dry season, the recharge water in floodplain wetlands is released to shorten the dry time and maintain the base flow of riverine wetlands, thus regulating the river runoff [ 45 , 46 ].…”

“…Floodplain wetlands exist in areas with gentle terrain and intercept floods in the flood seasons. Through hydrological connections, water resources can be released slowly during dry seasons, and the dry-up time of downstream rivers can be shortened to maintain the basic flow of rivers, and achieve the regulation of river runoff [ 45 , 46 ]. From 1988 to 2015, 17.10% of the riverine wetlands in the source region of the Yangtze River have been transformed into floodplain wetlands [ 22 ].…”