**1. Introduction**

In a shallow water body, beach changes may take place owing to wind waves. In a narrow water body with a large aspect ratio, the angle of wind waves relative to the direction normal to the shoreline may exceed 45°, and the shoreline may become unstable because the fetch distance in the direction of the principal axis of the water body is sufficiently large for waves with significant energy to be generated [1, 2]. Therefore, cuspate forelands that develop from both shores of a narrow water body connect with each other, resulting in the segmentation of the water body into smaller rounded lakes [3, 4]. For example, **Figure 1** shows the segmentation of a lagoon facing the Chukchi Sea in Russia [3, 4]. In this example, five elliptic lakes can be observed as a result of segmentation, and their axes are parallel to each other. **Figure 2** shows an enlarged satellite image of the rectangular area in **Figure 1**, and in this image, lake segmentation at a primitive

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

Japan. Then, the BG model was used to investigate the segmentation of a shallow water body with a triangular or crescent shape, and 3-D beach changes during the segmentation of a shal-

Segmentation of Water Body and Lakeshore Changes behind an Island Owing to Wind Waves

http://dx.doi.org/10.5772/intechopen.72550

51

When wind waves are incident to the lakeshore in a closed water body with a rocky or sandy island, topographic changes may occur on the lee of the island because of the wave-sheltering effect. Since a rocky island is fixed at a location in a closed water body, the wave-sheltering effect of the island is constant with time, and the lakeshore converges to a certain stable form after the wave action for a sufficiently long time. When a sandy island is located in a closed water body, however, the island itself can deform owing to the action of wind waves, resulting in the successive change in wave field. Thus, more complicated lakeshore changes will occur. Here, Lake Balkhash located in Kazakhstan [9] was selected as an example, and the BG model was used for

**Figure 3** shows an example of segmentation and the development of sand spits along the lakeshore of Lagoa de Mangueira (location: 33°09′59"S, 52°49′32"W) in Brazil [7]. The crescent lake is 100 km long and 10 km wide at the center of the lake. Many cuspate forelands have developed along the lakeshore and, in particular, the intervals of the cuspate forelands formed on the west shore become short near the south end of the lake. On the other hand, sand spits with similar shapes and cuspate forelands have developed along the east and west shores, respectively, in the north part of the lake. This is a typical example of segmentation

**Figure 4** shows a satellite image of an abandoned inlet located at the east end of Lake Saroma in Hokkaido, Japan (Location: 44°08′03"N, 143°59′04″E) [10]. This water body has a triangular shape, and segmentation of a water body can be seen near the east end. When enlarging the rectangular area in the satellite image of **Figures 4** and **5** is obtained. For the wind rose in Lake Saroma, the predominant wind direction is WNW, resulting in the eastward development of sand spits. On the south shore is Tofutsu fishing port, as shown in **Figure 5**. East of

**Figure 3.** Segmentation and development of sand spits along lakeshore of Lagoa de Mangueira in Brazil [7].

predicting lakeshore changes when a rocky or sandy island exists in a circular lake.

low water body into small lakes were predicted.

**2. Examples of cuspate forelands in lake**

and the development of sand spits in a crescent lake.

**2.1. Lakeshore in Lagoa de Mangueira**

**2.2. Lakeshore in Lake Saroma**

**Figure 1.** Example of segmentation of slender water body: Lagoons facing Chukchi Sea [3, 4].

stage can be seen with the alternate development of cuspate forelands. Regarding these phenomena, the division and reduction of the fetch distance owing to the formation of a large shoreline protrusion associated with shoreline instability under high-wave-angle conditions and the resulting change in the wave field are key factors. Ashton et al. [4] predicted that the forelands formed along the shoreline connect with each other, resulting in the segmentation of the water body into smaller rounded lakes. Uda et al. [5] predicted the three-dimensional (3-D) segmentation of a shallow rectangular water body using the BG model (a model for predicting 3-D beach changes based on Bagnold's concept) [6]. Uda et al. studied the emergence and mergence of small lakes and their segmentation using the same model [7], assuming that the wind blew from all directions between 0 and 360° with the same probability of occurrence and intensity, that is, a circular distribution of the probability. The segmentation into elliptic shapes, as shown in **Figure 1**, was not predicted in their study. It may be accomplished, assuming that the probability of occurrence of the wind direction is given by an elliptic distribution, similarly to the case of oriented lakes [8]. In this study, the segmentation of a rectangular water body was predicted, given a circular or elliptic distribution of the probability of occurrence of the wind direction.

In the coastal area, the segmentation of a shallow water body with a triangular or crescent shape can also be observed. To study the mechanism of segmentation of such a water body, several examples of segmentation together with the development of sand spits along the lakeshore were examined in Lagoa de Mangueira in Brazil, Lake Saroma and Lake Kitaura in

**Figure 2.** Enlarged satellite image of rectangular area in **Figure 1**.

Japan. Then, the BG model was used to investigate the segmentation of a shallow water body with a triangular or crescent shape, and 3-D beach changes during the segmentation of a shallow water body into small lakes were predicted.

When wind waves are incident to the lakeshore in a closed water body with a rocky or sandy island, topographic changes may occur on the lee of the island because of the wave-sheltering effect. Since a rocky island is fixed at a location in a closed water body, the wave-sheltering effect of the island is constant with time, and the lakeshore converges to a certain stable form after the wave action for a sufficiently long time. When a sandy island is located in a closed water body, however, the island itself can deform owing to the action of wind waves, resulting in the successive change in wave field. Thus, more complicated lakeshore changes will occur. Here, Lake Balkhash located in Kazakhstan [9] was selected as an example, and the BG model was used for predicting lakeshore changes when a rocky or sandy island exists in a circular lake.
