{"id":1316,"date":"2026-05-12T21:47:34","date_gmt":"2026-05-12T21:47:34","guid":{"rendered":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/fracture-properties\/"},"modified":"2026-05-13T03:24:38","modified_gmt":"2026-05-13T03:24:38","slug":"fracture-properties","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/basic-hydrogeology-an-introduction-to-the-fundamentals-of-groundwater-science\/chapter\/fracture-properties\/","title":{"raw":"16.3 Fracture Properties","rendered":"16.3 Fracture Properties"},"content":{"raw":"
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Orientation<\/h3>\r\n
\r\n\r\nFractures are three\u2011dimensional structures that are generally assumed to be planar or close to planar. Therefore, just like any planar structure we can characterize the orientation with strike and dip, where the strike<\/em> is the line created by the intersection of the fracture with the horizontal plane, and the dip<\/em> is the angle of the fracture plane below the horizontal plane. We can measure these orientations in the field or on aerial photographs, and then use rose diagrams (Figure\u00a0126<\/span><\/a>), radial plots, or stereonets to present the distribution of these orientations.\r\n\r\n<\/div>\r\n
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\r\n\r\nFigure\u00a0126\u00a0\u2011\u00a0<\/strong>Sample bi\u2011directional rose diagram showing the strike direction of fracture sets in a rock formation with the length of the rose petal representing one of a variety of features such as the frequency of fractures in that set relative to all fractures in the rock, the length of the fractures in that set, the average magnitude of their dip. The numbered labels represent the 4 main fracture set directions.<\/span>\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n
\r\n\r\nRose diagrams can be plotted on maps to show fracture trends and changes in orientation throughout a region. These diagrams can identify sets of fractures, which can then be related to groundwater flow directions using several methods, such as geochemical tracers.\r\n\r\n<\/div>\r\n<\/div>\r\n
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Aperture<\/h3>\r\n
\r\n\r\nFracture aperture is the distance between the fracture walls (Figure\u00a0127<\/span><\/a>).\r\n\r\n<\/div>\r\n
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\r\n\r\nFigure\u00a0127\u00a0\u2011\u00a0<\/strong>Fracture aperture and asperities on fracture wall.<\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\r\n\r\nIn an idealized fracture with smooth walls and a constant aperture\u2014that is, the fracture walls are parallel to each other\u2014the hydraulic conductivity and the discharge are proportional to the aperture. However, rock fractures always have asperities<\/em> that stick out from the wall of the fracture. These affect the properties of the fracture in the following ways.\r\n\r\n<\/div>\r\n