13.1 Introduction

This book is about groundwater, and to this point the material has dealt with the physics, mathematics, and chemistry of groundwater flow systems. However, groundwater is directly linked to the surface water component of the hydrologic cycle. The freshwater cycle—including precipitation, evaporation, infiltration, runoff, and accumulation in surface reservoirs—is the primary source of recharge to, and discharge from, the groundwater. In addition to sustaining groundwater, the water cycle (Figure 98) is the source of water for people, agriculture, and industry, thus it is important to have a basic understanding of the system. This section discusses surface water and the interactions between surface water and groundwater.

Figure 98 ‑ The hydrologic cycle (reproduced from US Geological Survey website at https://www.usgs.gov/media/images/natural-water-cycle-jpg↗).