Scenarios of land use and dynamic hydrosedimentological Poxim

Ref: C0338
Scenarios of land use and dynamic hydrosedimentological
Poxim-açu river model using swat
Alda Lisboa de Matos¹; Antenor de Oliveira Aguiar Netto 1; Marinoé Gonzaga da Silva1*;
Anderson Vasco do Nascimento*1; Fábio Brandão Britto1; Gregório Guirado Faccioli1
1
Department of Development and environment, Federal University of Sergipe, São Cristovão
- Sergipe, Postal code: 49100-000, Brazil.
*Corresponding author. E-mail: [email protected]
Abstract
The using and the inadequate management of the soil can cause gradually the losing of its
productive capacity, thus entails the degradation of water resources. Knowing the water production and the sedimentation in a watershed is essential to assist in decision making about
how to best use and management of soil and water. The aim of this paper is to simulate alternatives scenarios of using and soil occupation and measure the production of water and
sediment to different land uses in the watershed in the Poxim-Açu River with a SWAT model.
The methods applied were hydrological monitoring, generation of matrix data and tabular,
definition of the sub-basin, the calibration and validation of the method, statistical analysis,
spatial assessment of the production of water and sediments. Three scenarios were simulated; the first was the replacement of the current land use for forest, the second was pasture
and the third was sugar cane. Among these scenarios, the one corresponding to sugarcane
showed the highest production of water and sediments, 479.36 mm and 1.19 kg ha-1 respectively. The largest reduction of water production and sediments were verified with the replacement of the current land scenario for the forest scenario, 477.37 mm and 0.15 kg ha-1
respectively.
Keywords: Modeling, production and water, sediments production.
Introduction
The inappropriate use of the soil contributes for the gradual loss of its productive capacity, causing contamination of water bodies for sediment and pollutants washed down by
rain. The intensification of human activity destroys the equilibrium and modifies the natural
ecosystems in many situations causing loss of biodiversity.
These facts demonstrate the need of careful and active environmental assessment in
areas susceptible to sediment production, implementing use planning and land occupation
that prizes conservation practices. The removal of vegetation associated with the type of culture used and rainfall erosivity are factors that contribute in a significant way to soil erosion.
In this context, mathematical models have been applied successfully for both conservation planning and for erosion control in basins (MACHADO et al., 2003). A major feature of
the models is to serve as a tool for planning, which can provide an estimative by performing
simulations of possible scenarios. The simulations can be made by projection or by complex
spatial distribution systems. The modeling allows identifying the gaps and clarifying the unProceedings International Conference of Agricultural Engineering, Zurich, 06-10.07.2014 – www.eurageng.eu
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known relationships seeking to clarify them through several attempts. That can lead to better
knowledge of such relationships and assist in the design of future research (CHRISTOFOLETTI, 2007).
Among the models that have been used for hydrological modeling and hydrosedimentological basin, the Soil and Water Assessment Tool (SWAT) is the one that stands out most.
The SWAT is able to describe a variety of events, such as the movement and the amount of
pesticides, sediments, nutrients and numerous factors that are part or interfere in the hydrological cycle (ARNOLD and FOHRER, 2005).
In this context the present work intended to study the production of water and sediments in an experimental basin with the assistance of SWAT model in order to know the relationship between use and land cover, geomorphological features and processes hydrosedimentological.
1 Materials and methods
1.1 Studied area
The experimental basin selected for this study has 3.03 km ² and is mostly occupied by
pastures and agricultural crops. The chosen region is located close to the main source of the
River Poxim-Acu in Serra dos Cajueiros, a village in Itaporanga d' Ajuda, in the state of Sergipe, which has as coordinates: 67 º 51 'South Latitude and 88 ° 01' West Longitude (Fig. 1).
This part of the river basin Poxim-Açu is inserted into the project called Preservando
Nascentes e Municípios (PPNM), which aims the reforestation in order to recover springs
and watercourses in this basin and in the river Siriri Vivo, this project is sponsored by Department of the environment and Water Resources of the State of Sergipe (SEMARH) in
partnership with the Society of Multiple Ecological Studies and Arts (SEMEAR).
The uses of the soil in the studied area are: pastures (55 %), agricultural /sugarcane
crops (29 %), forest (10 %), riparian forest (5 %), villages and districts (1%) The areas with
higher slopes are used for pasture (<50%). Pastures occupy both steeper slopes as the land
of lower slope, while other land uses are located in areas with smaller slope. The predominant soil types in the basin of Acu-Poxim are Litholic Neosols (59%), Litholic Neosols Eutrophic (1%) and Quartz-sand Neosol (41%).
Figure 1 - Representation of the basins in the state of Sergipe- Brazil, the studied area the basin of the
river Poxim is hightlighted.
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1.2
The model
The SWATT model was developed by the department of agriculture (Departament of
Agriculture, Agricultural Research Laboratory, and Temple Texas - EUA), in order to simulate
hydrological processes in basins. This model has as characteristic of being physics based,
incorporating regression equations which describe the relationship between the input and
output variables, requiring specific information about weather, soil properties, topography,
vegetation and soil management practices occurring in the basin.
The SWATT models the physics processes related with the water and the sediments
movement, the vegetation growth and the nutrients cycling. The model also has features like
the use of input data easily available, being computationally efficient, since with different river
basins management strategies, can be performed without excessive investment of time or
money, and allows users to study long-term impacts (NEITSCH et al, 2005).
2.3
The parameters of the model
The spatial information that should be provided to the SWAT model for modeling are;
Digital Elevation Model (DEM), climate, soil type, and land use. The soil maps and land use
were obtained from the Digital Atlas of Water Resources of Sergipe have vector format on a
scale of 1:400,000 (SERGIPE 2012).
The MDE used was the result of a project called Brasil em Relevo, from data generated
by the project Shuttle Radar Topography Mission (SRTM). Based on the digital processing of
these images, EMBRAPA - Satellite Monitoring - clipped state mosaics, and recorded with
the LANDSAT series products of Brazil. The data have Raster format, where the study area
is divided into regular grid cells in a specific sequence obtained from (MIRANDA, 2005).
For simulating the physical processes of the studied area, were used the following soil
parameters: its name, its number of layers, its hydrological group and its depth. Concerning
the number of layers, were considered the depth, the soil density available, the water capacity, the percentage of organic carbon, hydraulic conductivity, albedo, erodibility factor of the
layer, electrical conductivity, and percentage of clay, silt, sand and rock. The soil data were
obtained through collection and analysis of soil held in the catchment area of the river PoximAcu.
The climates series were obtained from pluviometric stations in Laranjeiras and Itabaiana and one weather station in Aracaju, located near the catchment area of Poxim-Acu, in
the towns of Laranjeiras with Latitude and Longitude -10.80 -37.15, -10.70 and Itabaiana with
Latitude Longitude -37.42, -10.95 and Aracaju with Latitude and Longitude -37.04. The daily
values of precipitation, maximum and minimum air temperature, solar radiation, wind velocity
and relative humidity, for a period of 22 years, beginning in January 1991 to June 2012 were
obtained from Aracaju’s weather station. Laranjeiras’s and Itabaiana’s stations provided only
precipitation data.
Calibration was applied to enable simulating scenarios of water and sediments production in different scenarios of soil use scenarios by replacing the current use of the land for
forest, pasture and sugarcane. The performance of the model was analyzed by visual comparison (hydrograph) and statistical measures. The statistical measures used were the coefficient of Nash-Sutcliffe efficiency (NSE) (Nash and Sutcliffe 1970), percentage of tendency
PBIAS, relation between the standard error and standard deviation of the observations, RSR,
root mean square error RMSE. The NSE represents the approximation of the values of the
simulation with the observed, and then the closer to one (1) for the value found results seem
to being more satisfactory. For values closer to 0.0 for PBIAS, RMSE, RSR indicate the accuracy of the simulation model. According Moriasi et al, (2007), satisfactory values to the
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NSE, PBIAS, RMSE and SNR measurements are respectively: > 0:50, PBIAS ≤ ± 15 <± 25,
below half the standard deviation and ≤ 0.70.
2
Results and Discussion
2.1 Calibration of hydrological model SWAT
The delineated area consists of 4 sub-basins and 29 units of hydrological response
(HRUs). For calibration of the SWAT model, the data flow for the period from October 15 th
to December 20 th in 2012 of Poxim Acu station and precipitation data for the same period
were selected. For lack of data calibration was not performed for sediment, which does not
preclude the study of their production due to changes in land use.
After the sensitivity analysis, to verify which parameters are most sensitive to changes
in the input parameters of the model. Thus the parameters changed to fit the model were the
CN2 - reduced by 20%; SOL_AWC and SOL_K - reduced by 50%; SOL_Z and SLOPE - reduced by 25%; ESCO - changed to 1; ALPHA_BF - changed to 12:55; GW_DELAY changed to 60 and CANMX - changed to 7.5. The initial calibrated values for the altered parameters can be verified in Table 1. After the calibration, the statistical measures obtained
were: NSE= 0.93, PBIAS = 14.20, RMSE = 0.06, RSR = 0,07.
Table 1- modified values in the calibration of SWAT model in the river basin Poxim- Açu/SE.
Parameters
CN2
SOL_AWC
ESCO
ALPHA_BF
SOL_Z
GW_DELAY
SLOPE
SOL_K
CANMX
Interval
Inicial value
±25
Pasture= 69
Sugar cane=77
Forest= 55
±50
0–1
0–1
±25
0 – 100
±25
±50
0 – 10
0.95
0.048
31
0
Final calibrated value
-20%
Pasture= 55.2
Sugar cane = 61.6
Forest= 44
-50%
1
0.55
-25%
60
-25%
-50%
7.5
CN2: Curve Number; SOL_AWC: Quantity of water available in the soil layer (mmH2O.mm-1solo); ESCO: compensation factor of soil evaporation; ALPHA_BF: Factor response to variations in aquifer recharge (days); SOL_Z:
depth of the soil layer (mm); GW_DELAY: Time groundwater (days) delay; SLOPE: average slope (mm-1)
SOL_K: saturated hydraulic conductivity; CANMX: maximum water storage in the treetops (mm H2O).
There was a better correlation between observed and simulated data in periods of low
precipitation (Fig. 2), it is observed that the model simulates the hydrograph peaks that do
not appear in the observed data. This fact can be explained by a failure of the observer at the
time of reading or the distribution of rainfall in the study area was unrepresentative in that
period. This situation was also evident in research (Malutta, 2009). The simulation of water
and sediments production for scenario1, i.e.: scenario for the current soil use. In all subbasins delineated, pasture and crops / sugar cane, are the predominant soil uses. In this
scenario the highest production values of water are in the sub-basins (3:04) with smaller
slope and greater vegetation cover and riparian forest. The sub-basins 1 and 2, have more
than 30% of the area with slopes between 20 - 40%, characterized as tightly curled (EMBRAPA, 2006), were higher in the values of sediment production (Fig. 3).
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Precipitation (mm)
Water Production (mm)
15 Oct 22 Oct 29 Oct 05 Nov 12 Nov 19 Nov 26 Nov 03 Dec 10 Dec 17 Dec
Precipitation
Observed
Simulated
Figure 2- Hydrograph of daily flow for the period calibration
Lopes et al. (2008), confirm that areas with higher slopes have higher sediment yield. It
is noteworthy that these areas have soils Litholic Neosols, are characterized by a few developed and susceptible to erosion especially in hilly areas. The lower production of water and
sediment was observed for scenario 2 land uses by forest (Fig. 3).
According to Lopes and Kobiyama (2008) sediment production is linked to the uses and
cover and relief. The lowest sediment production in this scenario is due to the protection of
the soil and the action of raindrops and increase in surface roughness (MACHADO et al.,
2003), reducing erosion and therefore sediment yield. The reduction in water production is
due to the increase of the infiltration process and reduction of surface runoff, causing thereby
reducing the production of water. Lelis and Calijuri (2010) affirm that this type of coverage
promotes greater interception of raindrops in the forest the treetops promoting greater interception of raindrops, providing greater protection of the soil and improving soil characteristics, giving a higher permeability. The forests act as a filter for sediment production and other
suspended solids runoff (USDA).
Blainski et al. (2010) observed that agricultural activities cause significant changes in the
volume of river flow due to different water demands of crops and management systems, and
in reforestation scenario compared to other scenarios, the river flow was maintained for
longer above the ecological flow.
Forest
Pasture
Sugar cane
Actual
Forest
Pasture
Sugar cane
Sediments Production (ton.ha. year-1)
Water Production (mm. year-1)
Actual
Figure 3 - Water Production (A) Sediments (B) in the sub basins of river Poxim-Açu.
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In scenario 3, when the entire area was considered as pasture, water and sediment
production remained without much change to the current soil use. This observation is due to
the fact that this watershed is predominantly occupied by pastures (59.5%), thus showing no
major changes. Already change the current land use for scenario 4, occupied by sugarcane
area, and represented the highest yields of water and sediments in relation to other scenarios.
Just like Lino et al. (2009), among the analyzed scenarios, scenario 4 (sugarcane)
showed higher surface runoff, increasing water production, unlike scenario 2 (forest) with the
lowest water production. Thus areas with agricultural crops that have higher production areas
occupied by pastures sediments. U.S studies have shown that erosion in acreage accounts
for 38% of the sediment yield, while the pastures are responsible for 26% (USDA, 1991).The
sediment production in scenario 4 (cane sugar) increased by 93% compared to the current
scenario, while in scenario 2 (forest), sediment production was also reduced by 75% compared to the current scenario.
One of the characteristics of agricultural crops is the seasonality, and sugarcane is an
example, as will planting season or cutting coincides with the rainy season, so the soil is unprotected of vegetation favoring runoff and processes erosion. According to Machado et al.
(2003) in sugar cane grown to the flow of rain water on the surface area tends to be larger in
area than native vegetation.
3
Conclusions
In all scenarios of soil use to higher sediment production was observed in the subbasins of the areas with higher slopes, while larger water production were higher in subbasins located in the lower basin.
The production of sediment and water is directly related to changes in land use, showing the necessity of the use of good management practices and land use in order to ensure
the quantity and quality of water resources in the river basin Poxim-Acu, so the SWAT model
can be used as a tool in planning and management of a basin.
4
Acknowledgements
The project "Preservando Nascentes e Municípios", funded by the Department of Environment and Water Resources of the State of Sergipe - SEMARH, in partnership with the
Federal University of Sergipe. To CAPES (Coordenação de Aperfeiçoamento de Pessoal de
Nível Superior) for supporting and funding this research project.
5
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