In this paper, we proposed a method for mapping the suitability of land for intensive anthropogenic use in the Maranhao River Basin, in the state of Goiás, Brazil. We analyzed existing 1:250,000 maps of the local geology, drainage system topography and geomorphological features. We generated new information based on our analysis, including a compilation of basic morphometric data and a map of the slopes in the basin, which we used to construct the geomorphological suitability map of the watershed. Our results indicate that 40% of the study area can support intensive anthropogenic use; the remaining 60% of the basin area is categorized as “fragile” regarding the expansion of intensive land use.
Geomorphological studies have helped researchers understand topographical relief. According to [
It is important to analyze and understand a watershed’s morphology not only because of its role in the area’s geomorphology but also because watersheds are treated as major geographical units for planning and geo-envir- onmental analysis in Brazil. Morphometric analysis can help determine the capabilities and constraints of a watershed and its suitability for various anthropogenic uses.
In this study, fitness is defined as the capacity of relief to support human activities while minimizing the impact on the watershed. Thus, studying the geomorphological characteristics of a watershed has implications for its occupation and the use and management of its natural resources. The geomorphological characteristics of watersheds are instrumental for academic research and land use planning.
The hydrological behavior of a watershed [
[
In this sense, morphometric analysis can be considered an essential tool for the qualification of a watershed. The proper interpretation of a drainage network, including the local geology and morphology, can reveal numerous issues related to erosion, which is the principal element of physiographic and geomorphological processes [
Morphometric analysis assumes that quantitative data can serve as parameters for the physical qualification of the basin and its hydrosedimentological processes, characterizing them precisely and revealing their homogeneity, according to [
Given the current demand for water resources and growing concern about environmental problems at the local, regional and global scales, morphometric studies can play an important role in consistently characterizing watersheds. Thus, they can support integrated management by quantitatively describing the complex landscapes contained in a drainage basin.
Relief features have cartographic elements that are present in various sizes and shapes. Characterizing the sizes and shapes of these features is important in understanding their genesis and current dynamics, and their cartographic representation allows synthesizing their roles in a landscape. Therefore, geomorphological mapping and classification has been the subject of research and experimentation since the 1960s in various countries, particularly in Europe [
Different land uses (rural, agricultural, industrial and urban) in plains or on hillslopes are elements in a basin’s landscape and scenery. They can have various negative environmental impacts, including vegetation removal, pollution, and silting. Human activities occur at a higher intensity in urban areas because of the concentration and variety of economic activities in such locations that result in the degradation of natural resources [
Geomorphological mapping should consider both taxonomy and scale and aim to characterize various types of relief, grouping them into different classes. In general, maps can be presented as morphostructural domains, geomorphologic regions, geomorphologic units and model types [
When studying relief based on geomorphological units, model types and forms, it should be noted that other elements of the geomorphological system might require special attention. In particular, hydrographic information on land slope and morphometric drainage is important, including relief dissection parameters, such as drainage density, split ratios and the average length of channels. This set of morphometric parameters can be grouped into classes based on the different patterns of the existing relief in a certain geomorphological region.
A morphometric analysis of relief can also help subdivide it into different geomorphological units [
Therefore, geomorphological characterization is a fundamental basis for environmental studies. This study aimed to analyze morphometric variables in the Maranhão River Basin (DF-GO), Brazil and indicate its geomorphological suitability for various anthropogenic uses.
The mapping studies have used mapping studies of individualized form without the adequate incorporation of morphometric elements with the proposals of public policies for zoning of the territory. So in this text there is the proposal to analyze the potential of morphometric information for methodological advances in land planning policies.
The Maranhão River Basin is an important unit of study because it covers two states (Goiás and Tocantins) and the Distrito Federal in mid western Brazil. In addition, it is an important catchment area of the Araguaia- Tocantins water system (
This study used drainage and topography data from 1:250,000 maps to conduct a basic morphometric analysis of the basin. All calculations to identify the morphometric indicators followed the recommendations and equations proposed by [
The split ratio (LR) is the ratio of the total number of channels in a certain order and the total number of channels in the order immediately above. This ratio must be constant and can never be less than 2 [
expressed by the following equation:
where: N is the total number of channels in a particular order; and Nu+1 is the total number of immediately higher order channels.
The drainage density (Dd) describes the total length of channels within a catchment area (in square kilometers). According [
where: Lt is the total length of the channels (km), and A is the total basin area (sq/km).
The river density (Dr) reflects the relationship between the number of streams and the area of a basin. This parameter is related to a basin’s ability to generate new fluids. This quantity is expressed by the following equation:
where:
N represents the total number of rivers or channels, and A is the area of the basin (km2).
The extension of the surface route (Eps) parameter is the average distance traveled by a flood between the interfluve and the permanent river. This variable is important because it represents the link between the hydrological and physiographic development of a drainage network. This quantity is expressed by the following equation:
where:
Eps is the extent of the surface route, and Dd is the drainage density.
The basin area (A) represents the entire area drained by a river system and is generally expressed in square kilometers. This ratio can be measured using conventional methods or more sophisticated methods using specific software.
The length of the entire channel (L) is distinguished from the length of each order of channels by the letter u. The sum of the lengths of each order of channels is Lu, and Lt represents the total length of all water bodies in a river basin.
The sinuosity index of channels (Is) relates the true length of the channels with the straight length between their extreme points. This parameter includes the influence of sediment load and the lithological and structural subdivisions [
where:
L is the channel length (km);
Dv is the vector distance (km) between the extreme points of the same channel.
Values close to 1 indicate high structural control (high energy), and values above 2 indicate low power; intermediate values generally characterize transitional forms between straight and meandering channels.
In this study, we selected slope classes based on the work of [
We added a classification of six levels of use to the class table [
Our methodology was based on a spatial analysis of the information layers (PIs) in a geographic information
Class | Slope Angle | Landform | Process Erosion | Activities | Suitability* |
---|---|---|---|---|---|
1 | 0˚ - 2˚ | Floodplains, terraces, and surface erosion. | Minimal soil loss and no landslides | Mechanized agriculture, urbanization, and roads. | High |
2 | 2.1˚ - 5˚ | Soft ripples, valley bottoms, and tabular surfaces. | Start of solifluction, diffuse and laminar flow; furrows. | Some conservation farming. Acceptable for urbanization. | High with limitations |
3 | 5.1˚ - 15˚ | On hillsides, monoclines, and structural reliefs. | Mass movements, creeping laminar flow, landslides, furrows, and ravines. | Moderate to intense conservation farming. Mechanization impossible >7º. Poorly suited for urbanization and infrastructure routes. | Moderate |
4 | 15.1˚ - 25˚ | Mountainous slopes, escarpment failures and terraces. | Strong linear erosion, soil destruction, landslides and falling blocks. | Farming and forestry. Unfit for urbanization and infrastructure. | Moderate with restrictions |
5 | 25.1˚ - 35˚ | Hogback-type structural relief, coastal cliffs, and ridges. | Strong linear erosion, destruction of soil, landslides, falling blocks, and avalanches. | Forest use. | Partly restricted |
6 | >35˚ | Walls and cliffs in canyons or very enclosed valleys, and cornices. | Mass falls, landslides, and collapses. | Limited forest use. | Restricted |
Text adapted from [
system: a) topography, b) geomorphology, c) drainage channels, d) slope, and e) ecological economic zoning. The data contained in these layers provided in information to support the final analysis.
The basin includes significant numbers of first- and second-order channels, indicating that the drainage headwaters have caused intense dissection of relief. The channel bifurcation ratio is slightly greater than 2, suggesting a relief configuration with a general hilly trend.
Graphing the relationship between the number of channels and the hierarchical order of the streams that constitute the basin (
Understanding the implications of this bifurcation ratio (Rb) for relief and, thus, anthropogenic use is of paramount importance when characterizing the environmental fragility of lower-order waterways. For hydrogeomorphological management, awareness of the intense processes of natural and anthropogenic erosion in the basin’s headwaters is required. This is especially important in the Maranhão River Basin, which includes more than 690 first-order channels, representing 49.3% of the basin’s channels.
Board 1 shows the other major indices that were important inputs for creating the suitability classes: the drainage density (Dd), river density (Dr), and extension of the surface route (Eps). For the Maranhão River Basin, the drainage density and river density are relatively low, indicating lower relief. Thus, other elements must be observed outside the area for a hydrographic basin of this size.
The morphometric parameters of the main drainage channel can helpcharacterize the river basin. Among these, the sinuosity index (Is) is the relationship between the channel length and the vector distance from the ends of the main channel. When Is ≅ 1.0, the channel tends to be straight, whereas when Is > 2.0, the channel tends to be tortuous.
Intermediate values of Is indicate transitional, regular and irregular shapes. Sediment load, lithology, geological structures and channel slope all influence the sinuosity of the channels.
Order | Number of segments | Rb | L(m) | Rlm |
---|---|---|---|---|
1 | 693 | 2.288 | ||
2.02 | 1.51 | |||
2 | 342 | 3.501 | ||
2.15 | 1.04 | |||
3 | 159 | 3.643 | ||
2.23 | 1.29 | |||
4 | 71 | 4.732 | ||
2.44 | 0.91 | |||
5 | 29 | 4.317 | ||
2.41 | 1.20 | |||
6 | 12 | 5.213 | ||
2.40 | 0.89 | |||
7 | 5 | 4.680 | ||
2.5 | 0.98 | |||
8 | 2 | 4.590 | ||
2 | 2.08 | |||
9 | 1 | 9.560 |
Board 1. General morphometric parameters of the Maranhão River Basin’s hydrography.
The longitudinal profile of the main channel shows its slope (
The geomorphological map of Maranhão River Basin was adapted from the work of [
After comparing the PIs, we created a suitability relief map showing the distribution of slope classes associated with the geomorphological map and other spatial information (
Anthropogenic use corresponds to 25.67% of the area of the basin and is distributed among the suitability classes, indicating a high degree of control over the relief (
Morphometric parameters | |||
---|---|---|---|
Dd = 0.444 | Dr = 0.084 | Eps = 1.126 meters | Ic = 0.330 |
The classes proposed in this study were compared with the suitability classes from the Economic Ecological Zoning (ZEE) of the State of Goiás and the Distrito Federal (
Class | Area (km²) | % in basin | Suitability | Anthropogenic use (km²) | % in class |
---|---|---|---|---|---|
1 | 2022.52 | 13.1 | High | 760.34 | 37.6 |
2 | 4181.42 | 26.9 | High with limitations | 1514.48 | 36.2 |
3 | 5827.92 | 37.4 | Moderate | 1344.65 | 23.1 |
4 | 2175.47 | 14.0 | Moderate with restrictions | 273.61 | 12.5 |
5 | 896.89 | 5.7 | Partly restricted | 81.08 | 9.0 |
6 | 449.97 | 2.9 | Limited | 21.45 | 4.7 |
15,554.19 | 3995.62 |
anthropogenic use. In contrast, based on morphometric parameters, this percentage is at most 40% (13.1% + 26.9%). Furthermore, the ZEE indicates that 21% of the area should be considered to be restricted, whereas the morphometric approach includes three levels of restricted activity affecting 22.6% of the area.
We conclude that applying morphometric analysis of the basin to determine the suitability of areas for anthropogenic use represents an improvement over previous methods because it results in a higher level of detail. In addition, it highlights some inconsistencies in the ZEE results.
This study sought to use spatial analysis to determine the suitability of land in a watershed for anthropogenic use. Spatial analysis of the morphometric parameters of a basin can support qualitative analysis, and this method could be incorporated into the zoning process. We suggest that this quantitative approach is necessary in the context of determining subsidies for territorial development and environmental management procedures.
It highlights the contribution of morphometric measures extracted in the scale of 1:250,000 in particular where articulated with the geomorphological features for a proposed new regional configuration of class stated for the land uses according to the degree of impact they can generate.
This text certainly is a landmark for future studies in the same watershed in more detailed scales, which may further contribute to the sustainable planning for the anthropic uses.
The authors thank their institutions Education and Research (UNB and UEPG) the opportunity to develop a collaborative work carried out under the technical cooperation agreement in the 2012 period to 2015.
Valdir A. Steinke,Ercilia Torres Steinke,Mario Diniz Araujo Neto,Maria Ligia Cassol Pinto, (2016) Proposed Relief Map of the Suitability of the Maranhão River Basin, Brazil, for Anthropogenic Use. Journal of Geographic Information System,08,351-360. doi: 10.4236/jgis.2016.83030