{"id":1284,"date":"2026-05-12T21:47:23","date_gmt":"2026-05-12T21:47:23","guid":{"rendered":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/distribution-of-water-in-the-shallow-subsurface\/"},"modified":"2026-05-13T03:21:45","modified_gmt":"2026-05-13T03:21:45","slug":"distribution-of-water-in-the-shallow-subsurface","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/distribution-of-water-in-the-shallow-subsurface\/","title":{"raw":"14.2 Distribution of Water in the Shallow Subsurface","rendered":"14.2 Distribution of Water in the Shallow Subsurface"},"content":{"raw":"
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Saturation<\/h3>\r\n
\r\n\r\nAt the surface of the Earth, the soil, sediment, or rock have some porosity, and some fraction of that porosity contains water. Thes fraction of porosity that contains water is called the degree of saturation<\/em> ([latex]S_{d}[\/latex]) and is defined in Equation\u00a0(106)<\/span><\/a>. This quantity can be expressed as a fraction or, if multiplied by 100, as a percentage.\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
<\/th>\r\n[latex]S_{d} = \\frac{{volume}_{water}}{{volume}_{voids}}[\/latex]<\/th>\r\n(106)<\/span><\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nThe degree of saturation tends to increase with depth, and the point at which the degree of saturation reaches 100\u00a0percent marks the boundary between the saturated zone<\/em> below and the unsaturated zone<\/em> above (Figure\u00a0110<\/span><\/a>).\r\n\r\n<\/div>\r\n
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\r\n\r\nFigure\u00a0110\u00a0\u2011\u00a0<\/strong>Cross\u2011section showing the distribution of water in the subsurface.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n\r\nThis boundary is often considered to be the same as the water table,<\/em> which we previously defined as:\r\n\r\n<\/div>\r\n