Topographic Structure

[Yaima President]

Topographicmaps refer to a graphical representation of the three-dimensional configuration of the surface of the Earth. Moreover, such maps show the size, shape, and distribution of landscape features.

Also, such maps present the vertical and horizontal positions of those features whose representations take place. Most noteworthy makes use of contour lines so as to show different elevations on a map.

Relief: The depiction of the relief aspect is with brown contour lines that represent the mountains, hills, valleys, plains, etc. The elevations are available in meters (or feet) above the mean sea level.

Furthermore, there are also spot elevations are shown in the black colour. Moreover, in these spot elevations, the marking of the lake level, the summit of a hill, or the road intersections takes place for the purpose of elevation.

Germany- Each federal state of Germany is in charge of producing official topographic maps. Moreover, the production and publishing of the maps which are between 1:5000 and 1:100000 take place by the land surveying offices of each federal state.

Israel- The Survey of Israel has the responsibility for carrying out the topographic and civilian mapping of Israel. Moreover, the standard map scales in Israel are 1:50000 and 1:100000. Also, one can access the 1:50000 map online. Above all, Israel is a country that contains many high elevation places.

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Structural hydrological connectivity has been proposed to describe the geological structure of the landscape as well as to explain hydrological behaviors. Indices based on the topological or soil condition were developed to interpret their relationships. While previous studies mainly focused on well-instrumented catchments which are narrow in humidity or temperate zone, the hydrological responses to structural connectivity at the plot and hill slope scale as well as in arid or semi-arid climate conditions remain unclear. This study was conducted in the semi-arid mountainous region of northern China in Haihe Basin which is the source of water of about 350 million people. Experiments were conducted during the rainy season in 2012 and 2013 using four runoff plots. Two indices, flow path length (FL) based on topography and integral connectivity scale length (ICSL) based on soil moisture conditions, developed to represent hydrological connectivity structure and the runoff response to rainfall were analyzed. The results showed that the surface runoff coefficient was strongly and positively linearly correlated to FL, and the correlation between subsurface flow and ICSLs was quadratic. Plots with shorter FL required more rainfall to generate surface runoff. In the shallow soil layer, when the ICSLs are relatively low, the soil can store more water and less rainfall feeds subsurface runoff. Further analysis indicated that improved shallow soil connectivity conditions might enhance the water-holding capacity and lead to lower water yields for each event. This study demonstrated that hydrological structure connectivity could explain the mechanism of runoff generation in semi-arid areas while further experiments should be undertaken to find the threshold-like relationship between FL and surface runoff as well as the influence of plant cover on hydrological behaviors.

In recent years, the concept of hydrological connectivity has been proposed and studied to describe the geological/ecological structure of the landscape as well as to explain both hydrological behavior and the relationship between hydrological and ecological processes1,2,3,4,5,6,7,8. Despite different concepts of this new term emanating as a function of the different types of environments studied and research scales used9, the common view is that the configuration of geological units (including vegetation, soil moisture, and topographical characteristics), along with climatic conditions, influence the processes of water-mediated transport of matter, energy, and organisms10,11. This configuration is considered static or structural hydrological connectivity, while the processes denote the dynamic or functional components9.

Static or structural hydrological connectivity refers to the spatial pattern of hydrological response units12 and has been studied for decades13,14,15,16. Some indices have been well developed for this purpose9 and the most commonly used methods include semivariograms17,18, entropy13,17, binarization by threshold9,17, flow path length (FL)16, and integral connectivity scale length (ICSL)13,17,18. Ali et al. (2010) tested almost all of these structure metrics in a small catchment and found that only a few metrics were significantly correlated with both meteorological conditions and hydrological responses at the outlet. Mayor et al. (2008) proposed the use of the FL method for capturing the connectivity structure at both the plot and watershed scales and demonstrated that the surface runoff response could be well explained by this index. ICSL based on soil moisture data has been reported in an extremely limited number of references13,17,19,20 because of the complexity in its measurement and calculation. It has, however, been recommended as an efficient method for capturing hydrological structure patterns9,13,20, especially soil moisture conditions17, which play an important role in runoff generation21,22,23.

The aims of this work were three-fold: (1) collecting hydrological data at the study site, (2) measuring the hydrological connectivity structure based on soil moisture conditions and topographic metrics, and (3) linking the relationship between runoff generation and structural hydrological connectivity to obtain a better understanding of hydrological processes in the semi-arid mountainous areas in north China.

Relationship between ICSL and SSFC for all events in the four runoff plots. S, M, and L refer to the ICSLs in the small, medium and large rainfall events, respectively. ICSL3, ICSL5, and ICSL7 refer to threshold values of 0.3, 0.5, and 0.7, respectively.

Uncertainty exists in the current and previous studies. The number of plots was too small to check if there is a threshold-like relationship between FL and surface runoff which was assumed by some studies (Bracken et al., 2013; Bachmair and Weiler, 2014a).

Moreover, structural hydrological connectivity provides us with a new perspective to understand geological/ecological structures33,54. Studies should pay more attention to the relationship between hydrological connectivity and other ecological functions55 such as nutrient transmission56, sediment yield57,58, and the distribution of species5. For example, sedimentation generation was not discussed in this study; however, it would be meaningful in water and soil conservation efforts and even landslide prevention if a relationship between erosion and hydrological process could be established. Only in this way can we apply the concept of hydrological connectivity to the restoration of ecosystems, the management of water resources, or the preservation of habitat of endangered species. This is far more important and meaningful than studying the hydrological connectivity itself.

This work measured two structural hydrological connectivity indices based on the soil moisture conditions and topography in the mountainous area of northern China. Surface runoff generation showed a significant positive linger relationship with precipitation in plots with longer FL, and surface runoff coefficient was positively correlated to FL. Meanwhile, the ICSL did not show a specific relationship to SSFC. Further analyses showed that better shallow soil connectivity conditions might enhance infiltration and water-holding capacity. The results of this study are potentially useful in water resource management as water generation can be adjusted by modifying the structural hydrological connectivity. There are many factors that could influence connectivity at the plot scale including micro-topography and forest structure. While the results of this work revealed the linkage between structural connectivity and water yield processes at the plot scale, some of the results could be used to inform water and soil retention projects in areas similar to the study area. However, further studies are required to understand its applicability at larger spatial scales.

Antecedent moisture condition (AMC) and plant distribution can influence hydrological processes8,59,60 as well as the hydrological connectivity structure5,57. Multiple methods to measure AMCs were introduced in the literature reflecting the different aims of the studies14,61. In the current study, the soil relative saturation index was used, which can be expressed as

As shown in Fig. 10, we considered the lowest point of each runoff plot as the zero elevation point and measured the relative elevation of each cell. FL is the Euclidean distance of the potential flow path based on the micro-topography of the experimental plots. Mayer et al. (2008) first proposed this method to measure the structural connectivity at both plot and catchment scales. A modified FL method was used to represent the surface structural connectivity and was based on the 8-connected pattern20. For example, the flow direction in runoff plot R4 was determined according to the elevation gradient (Fig. 3 R04a) calculated as

The three thresholds of 0.3, 0.5, and 0.7 were set, and the ICSLs of each precipitation event under the thresholds were calculated to analyze the relationship between structural connectivity and SSFC. The ICSL and area were calculated using the bwlabel function from the Image Processing Toolbox in MATLAB (The Mathworks, Inc.). More details can be found in Western et al. (2001) and Ali and Roy (2010).

3a8082e126