Water and Drainage

Water is the most widespread feature on the surface of the Earth, and water bodies exist in many forms—seas, lakes, rivers, ponds, estuaries, bayous, lagoons, etc. In aerial

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FIGURE 10-2 Vertical SFAP of a pond with emergent leaves of the American lotus (Nelumbo lutea). Individual leaves are clearly visible around the margin of the pond; these leaves are typically about one foot (30 cm) in diameter. The dock is ~ 15.5 m long. GSD for the original image is ~5cm, and the NIIRS rating is 8. Kite aerial photo by JSA, October 2006.

FIGURE 10-2 Vertical SFAP of a pond with emergent leaves of the American lotus (Nelumbo lutea). Individual leaves are clearly visible around the margin of the pond; these leaves are typically about one foot (30 cm) in diameter. The dock is ~ 15.5 m long. GSD for the original image is ~5cm, and the NIIRS rating is 8. Kite aerial photo by JSA, October 2006.

FIGURE 10-3 The man-made pond in the foreground trapped recent runoff and has a high content of yellowish-brown suspended sediment. The next pond downstream did not receive this sediment and has a clean, dark blue appearance. Central Kansas, United States. Kite aerial photo by SWA and JSA, May 2007.

photography water color is most obvious, and the color of water bodies is a good indication of suspended sediment. Clean water reflects blue light weakly, but reflectance drops off sharply for green and red light and is essentially zero for near-infrared radiation (see Fig. 4-17). Thus, clean water typically looks dark blue or sky colored in visible imagery.

FIGURE 10-4 Low-oblique view over a small, meandering stream channel (left) flowing into Tar Creek (right). Sun glint highlights water in the smaller channel; however, muddy water in the larger stream is barely visible through deciduous trees with sparse leaves in early spring, Miami, Oklahoma, United States. Helium-blimp aerial photo by JSA and SWA, April 2008.

FIGURE 10-4 Low-oblique view over a small, meandering stream channel (left) flowing into Tar Creek (right). Sun glint highlights water in the smaller channel; however, muddy water in the larger stream is barely visible through deciduous trees with sparse leaves in early spring, Miami, Oklahoma, United States. Helium-blimp aerial photo by JSA and SWA, April 2008.

FIGURE 10-5 Sun glint highlights tiny islands in the shallow Vainameri Sea south of Vormsi, Estonia. Kite aerial photo by JSA and SWA, August 2000.

Suspended sediment impacts the color of water, which depends on the sediment composition and turbidity (Fig. 10-3; see also Fig. 14-20).

Aerial photography of water bodies often displays sun glint and glitter (see Fig. 4-5). Although usually considered undesirable, under some conditions sun glint is advantageous for identifying small water bodies that would otherwise be difficult to distinguish (Fig. 10-4). Conversely, sun glint may aid recognition of small, emergent islands within larger water bodies (Fig. 10-5), and sun glitter may highlight the pattern of wind-driven waves on water surfaces (see Fig. 5-18). Water flooding also may assist in interpreting subtle relief variations in an area, revealing shallow depressions and drainage structures that otherwise would not be identifiable. Figure 10-6, for example, contributed to recognizing the importance of

FIGURE 10-6 Flooding caused by a beaver dam in the Jossa Valley near Mernes (Spessart), Germany. On the inundated floodplain between the Jossa River (J) and the main irrigation ditch crossing the upper part of the image (D), a multi-channel drainage network and small lake have developed. The water table also traces a series of parallel ditches running at right angles to the main ditch; they are the remains of "Riickenwiesen", a nineteenth century irrigation system. More recent drainage ditches are revealed by water and yellow-flowering buttercups in the lower image half. Field of view ~150m across. Hot-air blimp photograph by JBR, IM and A. Fengler, June 2001.

FIGURE 10-6 Flooding caused by a beaver dam in the Jossa Valley near Mernes (Spessart), Germany. On the inundated floodplain between the Jossa River (J) and the main irrigation ditch crossing the upper part of the image (D), a multi-channel drainage network and small lake have developed. The water table also traces a series of parallel ditches running at right angles to the main ditch; they are the remains of "Riickenwiesen", a nineteenth century irrigation system. More recent drainage ditches are revealed by water and yellow-flowering buttercups in the lower image half. Field of view ~150m across. Hot-air blimp photograph by JBR, IM and A. Fengler, June 2001.

beaver activity in floodplain evolution in a study by John and Klein (2004). Beavers in large numbers have inhabited the river systems of central Europe and North America until the middle ages and nineteenth century, and beaver-induced biogeomorphological processes can be expected to have influenced the floodplain sediments and alluvial soils significantly. This raises many exciting questions in fluvial geomorphology.

In color-infrared imagery, for which blue light is excluded, water bodies are usually dark blue to black regardless of suspended sediment or water depth (Fig. 10-7). This fact can be used to advantage for distinguishing muddy water from wet, bare soil of similar visible color (Aber et al., 2009). However, color-infrared images over water are subject to strong sun glint and opposition effects that degrade image interpretation (Fig. 10-8).

FIGURE 10-7 Color-visible (A) and color-infrared (B) views over Man-nikjarv Bog, eastern Estonia. The water pools are quite shallow (<1m) and clear. Submerged aquatic vegetation is visible in (A), but water pools are completely black in (B). Kite aerial photos by JSA and SWA, September 2001.

Stream, delta, and tidal channels of various sizes and types are the products of erosion and deposition by concentrated water flow. Such channels are integrated into patterns found in nearly all land and coastal regions of the world. Individual channels are recognized in airphotos by the presence of water, vegetation, shadows, and other characteristic features (see Fig. 5-8). Networks of channels define drainage patterns that are useful clues for interpreting the geology and geomorphology of the landscape (Fig. 10-9). Such patterns are developed at all scales and spatial resolutions from huge river systems covering subcontinental areas to tiny gully networks (Fig. 10-10).

10.3.2. Geomorphology

Geomorphological forms and processes are often highly influenced by water and drainage, especially on the spatial scales captured by SFAP. The high resolutions of SFAP here

FIGURE 10-8 Sun glint (A) and opposition effect (B) in oblique color-infrared images. Brightness contrast is so high that few features can be discerned in detail. (A) Nigula Bog and (B) Teosaare Bog, Estonia. Taken from Aber et al. (2002, figs. 11 and 12).

offer interpretation possibilities not given with conventional airphotos. While geomorphological processes forming the landscape cannot be seen directly in an aerial image, and rarely may be observed in the field, the correlative forms and deposits may become apparent to the skilled observer by characteristic shapes, patterns, and textures (Marzolff, 1999; Fig. 10-11). Smooth, homogeneous surfaces tell of soil sealed by splash erosion and crusting; dense networks of parallel rills and residual enrichment of stones on the surface may be the result of strong sheet-wash processes. Sediment fans of accumulated material patterned with desiccation cracks at the outlet of larger rills testify to their geomorphodynamic activity.

Beneath the edges of a wide gully cutting into a nearly flat glacis d'accumulation in Burkina Faso's Sahel (Fig. 10-12A), soil debris broken off the walls creates a distinctive pattern on the ground where it has not yet been washed away by runoff water. Clearly visible drainage lines have been carved within the gully by the first storms at the beginning of the rainy season. Some islands and peninsulas are left of the former surface, mostly where tree roots

Drainage Patterns
FIGURE 10-9 Schematic illustrations of drainage patterns that reflect underlying bedrock structure or sediment accumulation. Adapted from Drury (1987, fig. 4.4).

strengthen the ground. In spite of the obviously heavy sheet-wash processes, the gully rim itself is sharply edged above the washed-out hollows in the more erodible subhorizon (Fig. 10-12B). An explanation is offered by the polygonal pattern of the emerging grass cover on the surrounding glacis: the vertic character of the soil leads to the development of fine-webbed desiccation cracks. It is along these tension cracks that clumps of soil break off along the gully edge when the soil dries up again. Also, when water infiltrates through the cracks, not only vegetation development

Effect Rill Erosion

FIGURE 10-11 Rill erosion on fallow land in the Spanish Ebro Basin near Maria de Huerva, Province of Zaragoza. Hot-air blimp photography by IM (lower right corner, with remote control) and JBR, October 1995. White measuring stick in lower right corner is 2 m long. S, strong sheet wash with small rills; H, headcut of large rill; K, knickpoint where small rills merge and incise to form larger rill; F, sediment fan of accumulated material eroded from the rill; C, soil crusted by splash erosion and week sheet wash.

Gimp Erosion Terrain

FIGURE 10-11 Rill erosion on fallow land in the Spanish Ebro Basin near Maria de Huerva, Province of Zaragoza. Hot-air blimp photography by IM (lower right corner, with remote control) and JBR, October 1995. White measuring stick in lower right corner is 2 m long. S, strong sheet wash with small rills; H, headcut of large rill; K, knickpoint where small rills merge and incise to form larger rill; F, sediment fan of accumulated material eroded from the rill; C, soil crusted by splash erosion and week sheet wash.

Rill With Gully Erosion Bird View

FIGURE 10-12 Gully erosion near Gorom-Gorom, Province of Oudalan, Burkina Faso. (A) Piping processes (arrow) and desiccation cracks, traced by vegetation in the vertic soil of the glacis d'accumulation, play an important role in developing and shaping the gully. Field of view ~30 m across. Kite aerial photograph taken by IM, JBR and K.-D. Albert, July 2000. (B) Seen from the ground, the undercuts carved by runoff water flowing over the gully's edge become apparent. Soil clumps below the wall have broken off the rim along the desiccation cracks. Photo by IM.

FIGURE 10-12 Gully erosion near Gorom-Gorom, Province of Oudalan, Burkina Faso. (A) Piping processes (arrow) and desiccation cracks, traced by vegetation in the vertic soil of the glacis d'accumulation, play an important role in developing and shaping the gully. Field of view ~30 m across. Kite aerial photograph taken by IM, JBR and K.-D. Albert, July 2000. (B) Seen from the ground, the undercuts carved by runoff water flowing over the gully's edge become apparent. Soil clumps below the wall have broken off the rim along the desiccation cracks. Photo by IM.

FIGURE 10-13 Rill and gully erosion on an abandoned agricultural field near Taroudant, South Morocco. The main drainage lines have a dendritic pattern, while the small rill tributaries follow the parallel patterns carved by a bulldozer during land levelling some years previously. Field of view ~75 m across. Kite aerial photograph by IM, JBR, and A. Kalisch, March " ^ 2006.

is encouraged but also subsurface erosion, leading to overhanging walls and piping processes (Albert, 2002).

On the abandoned agricultural field heavily affected by soil erosion in south Morocco (Fig. 10-13), a natural dendritic pattern is linked to an anthropogenic parallel pattern. In a vain endeavor to stop gully erosion, the field was levelled with a bulldozer some years before. The resulting grooves now channel the surface runoff into thousands of small parallel rills, encouraging incision and subsurface erosion. The rills continue to merge into larger rills and gullies that retrace the former, pre-levelling drainage network. The statistical analysis of the drainage network shows that more than one-third of the total rill length is directly predetermined by the mechanical intervention (Kalisch, 2009).

A further example for the influence of agricultural treatment patterns on rill erosion is shown in Figure 10-14. The field in the lower right, situated in the Mesa landscape of the Spanish Bardenas Reales, had been plowed one year before the picture was taken. Rills of ~ 10-30 cm depth have developed due to inflowing water from the adjoining cuesta slope. The tillage direction has a clear influence on the course, depth, and distribution pattern of the rills. Such features are clearly related to the few torrential rainstorm events and usually are destroyed with the next tillage operation. However, the barely visible and measurable depression that the material loss has created in the terrain surface makes it likely that a similar rill system would develop in the same places during the next heavy rainstorm event.

On a neighboring field that has lain fallow for three years, a gully up to 1 m deep has been cut by the concentrated overland flow from the old furrows (Fig. 10-15; see also Gimenez et al., 2009). The super position of several tillage operations leads to a complex course of this linear erosion form that cannot be understood from the ground perspective (Plegniere, 2009). This example demonstrates the difficulties that may arise for integrating the factor of tillage direction into GIS-based erosion models.

Some 1800 m higher in elevation, the vertical view onto a 40° high-mountain slope (Fig. 10-16) presents an altogether different aspect of geomorphology. Here, vegetation patterns can be seen reflecting periglacial geomorphic processes. The freeze-thaw cycles in this alpine area have created solifluction lobes in the form of minute terraces. While the step's surface, which is stretched by soil creep, is without cover, the front of the each lobe is bordered by thick turf that retards the gelisolifluction process.

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  • hagosa
    What color is water in aerial photo?
    1 year ago

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