Study on the Applicability of the Exterior Condition Assessment to Evaluate The Physical Vulnerability of Check Dams

Check dams are a typical structural approach used in watershed disaster management systems. Currently, approximately 12,000 check dams have been estimated to be constructed on mountain streams in Korea. More than 90% of these have been constructed in the last 20 years. This rapid increase over a short period of time has attracted attention to the necessity of maintenance strategies for check dams. The purpose of this study is to examine the applicability of the exterior condition assessment to evaluate the degree of deterioration in check dams. We classify the typical damage types of check dams and describe its key characteristics. Moreover, we apply a modified version of the condition assessment for large dams to meet the characteristics of check dams.

Visual Harmony of Engineering Structures in a Mountain Stream

This study uses the cognitive factor of “visual harmony” to assess the visual quality of stream engineering in a mountainous region. Images of engineering structures such as revetments and submerged dams in the mountain streams of Taiwan were collected. Three image groups with different structures invaded by vegetation were used for a questionnaire survey, which yielded 154 valid samples. We used statistical analysis to develop a model of visual harmony H with respect to the percentage of visible greenery GR, that is, the perceived curve of vegetation change. A comparison of our data with the literature determined the upper and lower bound curves of the relationship between H and GR. We found that the physical elements of “softscape” and “hardscape”—namely, percentage of visible water WR, visible structure IR, and visible natural material on the structure NR—affected this relationship. Results show that H is equivalent to visual preference P, and both can be improved by better green visibility (increasing GR and GR < 50%), avoiding low water visibility (WR < 10%), or increasing the amount of visible natural material (NR > 0.9). High visibility of the structures (IR > 0.3) may decrease H and P. We ultimately propose a visual harmony or preference model concerning a combined physical indicator that comprises GR, WR, IR and NR. Results of this study could be helpful to improve or access the aesthetics of stream engineering design.

Extreme suction attachment performance from specialised insects living in mountain streams (Diptera: Blephariceridae)

Suction is widely used by animals for strong controllable underwater adhesion but is less well understood than adhesion of terrestrial climbing animals. Here we investigate the attachment of aquatic insect larvae (Blephariceridae), which cling to rocks in torrential streams using the only known muscle-actuated suction organs in insects. We measured their attachment forces on well-defined rough substrates and found that their adhesion was less reduced by micro-roughness than that of terrestrial climbing insects. In vivo visualisation of the suction organs in contact with microstructured substrates revealed that they can mould around large asperities to form a seal. We have shown that the ventral surface of the suction disc is covered by dense arrays of microtrichia, which are stiff spine-like cuticular structures that only make tip contact. Our results demonstrate the impressive performance and versatility of blepharicerid suction organs and highlight their potential as a study system to explore biological suction mechanisms.

Taxonomy, Distribution and Life Cycle of the Maghrebian Endemic Rhithrogena sartorii (Ephemeroptera: Heptageniidae) in Algeria

Despite being recorded in Algeria since the nineteenth century, the genus Rhithrogena has never been the object of a taxonomical study and no identified species is known from this country. Investigations of the relict mountain streams of El Kala, north-eastern Algeria, have led to the discovery of a Rhithrogena population. Morphological and molecular analyses identified the species as the Maghrebian endemic Rhithrogena sartorii, so far known only from neighboring Tunisia. We report on the species’ distribution, status, and life cycle and discuss its potential role as a bioindicator in environmental monitoring.

Phylogenetic biogeography of Leptohyphes (Ephemeroptera: Leptohyphidae)

Leptohyphes Eaton is one of the most species-rich American genera in Ephemeroptera, with 45 valid species distributed from south-central USA to Patagonia. Most species are distributed in central and northern Andes. Nymphs are frequent and abundant in mountain streams. We present a parsimony-based morphological phylogeny for the genus. Specific geographic records were studied using Hovenkamp’s protocol (barrier biogeography). Leptohyphes was recovered as a monophyletic group. The most ancient disjunction found in Leptohyphes separated Tepui-area from the rest of the Americas. Other interesting vicariant events were found, including the separation of eastern Atlantic mountains (Mata Atlantica) from the Andes; oriental and occidental slopes of the Andes; northern from central Andes; and northern Andes from Central and North America. An ancient tropical South American origin for the genus is supported, with a more recent diversification due to Andean orogeny. Clades and terminals reaching North America include few independent events of more recent range expansions.