{"id":1111,"date":"2026-05-12T21:46:13","date_gmt":"2026-05-12T21:46:13","guid":{"rendered":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/introduction\/"},"modified":"2026-05-13T15:59:24","modified_gmt":"2026-05-13T15:59:24","slug":"introduction","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/introduction\/","title":{"raw":"2.1 Introduction","rendered":"2.1 Introduction"},"content":{"raw":"
\r\n
\r\n\r\nOne of the fundamental equations that govern groundwater flow is called Darcy\u2019s law as shown by Equation\u00a0(2)<\/span><\/a>.1<\/a><\/sup>\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n
<\/th>\r\n[latex]Q = - K\\ A\\ \\frac{dh}{dl}[\/latex]<\/th>\r\n(2)<\/span><\/th>\r\n<\/tr>\r\n<\/thead>\r\n<\/table>\r\n
\r\n\r\nwhere (parameter dimensions are dark green font with mass as M, length as L, time as T):\r\n\r\n<\/div>\r\n<\/colgroup>\r\n\r\n\r\n\r\n\r\n\r\n\r\n
[latex]Q[\/latex]<\/th>\r\n=<\/th>\r\ndischarge (L3<\/sup>T-1<\/sup>)<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
[latex]K[\/latex]<\/td>\r\n=<\/td>\r\nhydraulic conductivity (LT-1<\/sup>)<\/td>\r\n<\/tr>\r\n
[latex]A[\/latex]<\/td>\r\n=<\/td>\r\ncross sectional area perpendicular to flow (L2<\/sup>)<\/td>\r\n<\/tr>\r\n
[latex]\\frac{dh}{dl}[\/latex]<\/td>\r\n=<\/td>\r\nhydraulic gradient, change in hydraulic head h<\/em> over a distance [latex]l[\/latex] (:)<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n
\r\n\r\nIn plain words, this equation states that discharge<\/em> (i.e., volumetric flow) through a cross\u2011sectional area<\/em> of a porous medium is directly and linearly proportional to the hydraulic gradient,<\/em> and the constant of proportionality that relates discharge to the hydraulic gradient is a quantity called the hydraulic conductivity<\/em>. The negative sign indicates that flow is in the opposite direction of the gradient.\r\n\r\n<\/div>\r\n
\r\n\r\nWe get into the details of the equation in other sections of this book, but for now, let us focus on the lowercase h<\/em> in the hydraulic gradient term\u2014that is, hydraulic head<\/em>.\r\n\r\n<\/div>\r\n<\/div>\r\n
\r\n\r\n
\r\n\r\n
\r\n
\r\n\r\n1 <\/sup>Units for all equation variables in this book are expressed in general terms of length (L), mass (M), and time (T); for example, units of volumes are expressed as L3<\/sup>, velocity as LT-1<\/sup>, and so on.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>","rendered":"
\n
\n

One of the fundamental equations that govern groundwater flow is called Darcy\u2019s law as shown by Equation\u00a0(2)<\/span><\/a>.1<\/a><\/sup><\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n
<\/th>\n[latex]Q = - K\\ A\\ \\frac{dh}{dl}[\/latex]<\/th>\n(2)<\/span><\/th>\n<\/tr>\n<\/thead>\n<\/table>\n
\n

where (parameter dimensions are dark green font with mass as M, length as L, time as T):<\/p>\n<\/div>\n\n\n\n\n<\/colgroup>\n\n\n\n\n\n\n
[latex]Q[\/latex]<\/th>\n=<\/th>\ndischarge (L3<\/sup>T-1<\/sup>)<\/th>\n<\/tr>\n<\/thead>\n
[latex]K[\/latex]<\/td>\n=<\/td>\nhydraulic conductivity (LT-1<\/sup>)<\/td>\n<\/tr>\n
[latex]A[\/latex]<\/td>\n=<\/td>\ncross sectional area perpendicular to flow (L2<\/sup>)<\/td>\n<\/tr>\n
[latex]\\frac{dh}{dl}[\/latex]<\/td>\n=<\/td>\nhydraulic gradient, change in hydraulic head h<\/em> over a distance [latex]l[\/latex] (:)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
\n

In plain words, this equation states that discharge<\/em> (i.e., volumetric flow) through a cross\u2011sectional area<\/em> of a porous medium is directly and linearly proportional to the hydraulic gradient,<\/em> and the constant of proportionality that relates discharge to the hydraulic gradient is a quantity called the hydraulic conductivity<\/em>. The negative sign indicates that flow is in the opposite direction of the gradient.<\/p>\n<\/div>\n

\n

We get into the details of the equation in other sections of this book, but for now, let us focus on the lowercase h<\/em> in the hydraulic gradient term\u2014that is, hydraulic head<\/em>.<\/p>\n<\/div>\n<\/div>\n

\n
\n
\n
\n

1 <\/sup>Units for all equation variables in this book are expressed in general terms of length (L), mass (M), and time (T); for example, units of volumes are expressed as L3<\/sup>, velocity as LT-1<\/sup>, and so on.<\/span><\/p>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"author":8,"menu_order":5,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1111","chapter","type-chapter","status-publish","hentry"],"part":1470,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1111","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/users\/8"}],"version-history":[{"count":4,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1111\/revisions"}],"predecessor-version":[{"id":1850,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1111\/revisions\/1850"}],"part":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/parts\/1470"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapters\/1111\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/media?parent=1111"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/pressbooks\/v2\/chapter-type?post=1111"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/contributor?post=1111"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/wp-json\/wp\/v2\/license?post=1111"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}