Simulation of Run-Off Induced Soil Erosion and Its Impact On Water Quality from A Watershed in Shivalik Foot-Hills

Abstract

Runoff-induced soil erosion is a non-linear phenomenon in the real-world hydrology. Soil loss due to surface runoff decrease land productivity and affect stream water quality. In this study the non-point water quality problems caused by soil erosion is estimated to design and evaluates alternative techniques for soil and water conservation planning. This is planned on the basis of priority in the selected upper Patiala-Ki-Rao watershed located in the Shivalik hills of SAS Nagar district of Punjab and Panchkula district of Haryana state, Northern India. High intensity and short period rains in the area are common and a large amount (35-45%) of monsoon rainfall runs downstream in the torrents causing flooding and severe soil erosion. The land in the area is undulated and the surface soils are easily dispersible and erodible. Agriculture is rain-fed in the area and the groundwater is too deep to further exploitation. The whole area is ecologically degraded. Thus, a strong need for a study that will help to quantify runoff, runoff induced soil erosion and its impact on water quality is required. It is envisaged, that it will help in the implementation of conservation measures at the watershed scale for natural resource management and planning in the region. To understand the watershed characteristics morphometric and hypsometric analysis was done out by using Remote Sensing and Geographic Information System (GIS). Soil, slope, and land use thematic layers were prepared and with the help of the GIS overlay technique, erosion vulnerable areas were identified based on priority by using the Analytical Hierarchical Process (AHP) proposed by (Saaty, 1980). Based on the Prioritization, the selected watershed was classified into three priority areas on the basis of susceptibility to erosion. Hydrologic models have been proved to be useful analytical tools for the simulation of runoff, soil loss, nutrients, etc., and finding solutions through changing land use and applying Best Management Practices (BMPs). In the present research, the SWAT model was used to check its applicability for simulating runoff, runoff-induced soil loss and nutrients for management and conservation of natural resources to rejuvenate the fragile ecosystem of Shivaliks. Spatial data and the limited observed data available for runoff and soil loss for four adjoining gauged micro micro-watersheds nested within the selected ungauged watershed were used to quantify stream flow, sediment yield and nutrients of the ungauged basin using regionalization approach. In the present study, monthly simulation of stream flow and sediment yield for the period 2004 to 2015 was done in which three year warm up period was taken to saturate the soil for initial runoff. Out of remaining nine years period first five years (2007-2011) was used for calibration and that of next four years (2012-2015) for validation of the model. The results of statistical analysis after thorough calibration and validation predict that the SWAT model can satisfactorily simulate stream flow and sediment yield for the upper Patiala-Ki-Rao watershed. The correlation coefficient (R2), model efficiency (NSE) and percentage bias (PBIAS) values during calibration period of five years were 0.99, 0.98, 13.9 and during validation period of four years 0.98, 0.96, 14.6 respectively for stream flow. For sediment yield, the R2, NSE and PBIAS values were 0.91, 0.98, 12.2 for calibration period and 0.89, 0.98, 14.1 for validation period respectively. Whereas simulated nutrients were used for general policy analysis rather than predictive purposes due to the lack of historic data of nutrients. The study also predicts a high amount of runoff and soil loss in the upper Patiala-Ki-Rao watershed. To check the impact of higher levels of runoff-induced soil loss, water quality parameters were assessed by collecting some water samples during monsoon season. On the basis of the average values of the parameters accessed for qualitative analysis, the stream water is considered suitable for irrigation except for the high levels of Total Suspended Sediments (TSS) and turbidity. Hence it is required to take some preventive measures to save runoff and control soil erosion and nutrients. However, before implementing management practices, the effectiveness of various BMPs in controlling runoff-induced soil loss and pollutants were assessed using the SWAT model. Results of the study predict the effectiveness of BMPs i.e. check dam, plantation, fencing, grass waterways, contouring and terracing for managing water, sediments and nutrients in the selected watershed. Whereas the cost-benefit analysis was done on the basis of nutrients that are preserved by the implementation of BMPs. Farm ponds are recommended for harvesting runoff water to fulfil several farm needs, such as the supply of the water to crops for protective irrigation, livestock, etc. and preventing lower-lying areas from flooding during heavy rains.