**Prediction of Surface Runoff and Soil Erosion at Watershed Scale: Analysis of the AnnAGNPS Model in Different Environmental Conditions**

Demetrio Antonio Zema, Giuseppe Bombino, Pietro Denisi, Feliciana Licciardello and Santo Marcello Zimbone

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50427

**1. Introduction**

Negative effects of surface runoff and soil erosion in watersheds can be controlled and miti‐ gated through hydrological models. Moreover, they are suitable to simulate various combi‐ nations of different scenarios of land and water management in a watershed and therefore they are useful for comparative analysis of different options and as a guide to what Best Management Practices (BMPs) can be adopted to minimize pollution from point and non‐ point sources (Shrestha et al., 2006).

Continuous simulation models (e.g. AnnAGNPS, WEPP, SWAT, etc.) provide great advan‐ tages over event-based models as they allow watersheds and their response to be studied over a longer time period in an integrated way. Nowadays, several continuous watershedscale erosion models are available: however, relatively little validation of their performance under varying climatic and land use conditions has been carried out. The latter is an essen‐ tial step before a model can be reliably applied.

The AnnAGNPS (Annualized Agricultural Non-Point Source) model (Geter and Theurer, 1998; Bingner and Theurer, 2001) is among the distributed models developed to evaluate the continuous hydrologic and water quality responses of watersheds. Many major hydrologic concepts of the single-event AGNPS model (Young et al., 1987) have been updated through the continuous simulation modeling of watershed physical processes (Baginska et al., 2003).

© 2012 Zema et al.; licensee InTech. This is an open access article 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. © 2012 Zema et al.; licensee InTech. This is a paper 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.

AnnAGNPS has been implemented to assess runoff water amount and quality as well as sediment yield in small to large monitored watersheds (ranging from 0.32 to 2500 km2 ) under different environmental conditions. Such applications were frequently coupled with calibration/validation trials. Poor AnnAGNPS predictions of sediment and nutrient loads were achieved in a Georgia watershed, covered by both extensive forest and riparian con‐ ditions and attributed this to the defective data input used with the model (Suttles et al., 2003). Moderate accuracy in model simulation of phosphorous and nitrogen processes was also highlighted by model applications in two small watersheds located in the Missis‐ sippi Delta (Yuan et al., 2005) and in the Sydney region (Baginska et al., 2003). The capa‐ bility of the model (coupled to the BATHTUB eutrophication reservoirs model) in simulating nutrients load variations in response to land use changes in a Kansas large res‐ ervoir was pointed out by Wang et al. (2005).

validation processes in a 136-km2 agricultural watershed in south-central Kansas; total phos‐ phorus predictions were instead good only for the calibration period (Parajuli et al., 2009). Finally, a poor model performance in simulating agricultural pollution by nitrogen, phos‐

Prediction of Surface Runoff and Soil Erosion at Watershed Scale: Analysis of the AnnAGNPS Model

(USA), mainly due to the large size of the study area and the high variability in land use and

Thus, the results of AnnAGNPS evaluations that have hitherto been carried out are general‐ ly promising. At the same time it can be noticed that model performance is variable and the boundary conditions under which the model may be successfully used for runoff and sedi‐

In order to consolidate use of the AnnAGNPS model in different climatic and geomorpho‐ logic conditions, this investigation has verified model prediction capability of surface runoff, peak flow and sediment yield in two small European watersheds under climate conditions typical of the semi-arid (Cannata watershed, southern Italy) and humid-temperate (Gans‐ poel watershed, central Belgium) environments respectively. Through this work we have in‐ vestigated to what extent AnnAGNPS may be expected to provide usable results in environmental conditions outside of research watersheds, where sometimes the necessary

AnnAGNPS is a distributed parameter, physically based, continuous simulation, daily time step model, developed initially in 1998 through a partnering project between the USDA Ag‐ ricultural Research Service (ARS) and the Natural Resources Conservation Service (NRCS). The model simulates runoff, sediment, nutrients and pesticides leaving the land surface and shallow subsurface and transported through the channel system to the watershed outlet, with output available on an event, monthly and annual scale. Required inputs for model im‐ plementation include climate data, watershed physical information, as well as crop and oth‐

Because of the continuous nature of AnnAGNPS, climate information, which includes daily precipitation, maximum and minimum temperatures, dew point temperatures, sky cover and wind speed, is necessary to take into account temporal weather variations. The spatial variability of soils, land use, topography and climatic conditions can be accounted for by di‐ viding the watershed into user-specified homogeneous drainage areas. The basic compo‐

nents of the model include hydrology, sedimentation and chemical transport.

watershed located in North Dakota

http://dx.doi.org/10.5772/50427

5

phorus and sediment was obtained in a 16.97-km2

management practices (Lyndon et al., 2010).

**2. Aim of the work**

**3. The AnnAGNPS model**

ment yield prediction have not been well defined.

data for model calibration and validation are not available.

er land uses as well as irrigation management data.

In applications to a small Mississippi watershed reported by Yuan et al. (2001, 2005), An‐ nAGNPS adequately predicted long-term monthly and annual runoff and sediment yield and predicted and observed runoff from individual events were reasonably close, achieving coefficients of determination r2 and efficiency E (Nash and Sutcliffe, 1970) equal to 0.94 and 0.91 respectively). In a small Australian watershed, mainly covered by farming and residen‐ tial land uses, acceptable model predictions (E = 0.82) were assessed for runoff at event scale after the calibration of hydrological parameters Baginska et al. (2003).

More recently AnnAGNPS was implemented at a small Nepalese watershed, mainly for‐ ested and cultivated, where the need of calibration for satisfactory runoff predictions was shown. Despite the calibration process, peak flow and sediment yield evaluation resulted in a much lower accuracy (Shrestha et al., 2006). The prediction performance of An‐ nAGNPS in a 48-km2 watershed located in Kauai Island (Hawaii, USA) was considered good for monthly runoff predictions and poor on a daily basis (Poliakov et al., 2007). Cal‐ ibration/validation tests in two small watersheds in S. Lucia Island (British West Indies) (agricultural and forested respectively) suggested that AnnAGNPS could be used under the conditions tested tested (Sarangi et al., 2007). In an agricultural river basin (374 km2 ) of Czech Republic suspended load following short duration intensive rainfall events was accurately predicted by the AnnAGNPS model; there the model was not suitable for con‐ tinuous simulation in large river basins with a high proportion of subsurface runoff (Kli‐ ment et al., 2008). In a 63-km2 watershed in Malaysia (tropical region which sometimes experiences heavy rainfall runoff) was well predicted while results with respect to sedi‐ ment load were moderate (Shamshad et al., 2008).

Some applications in Spanish catchments covered by olive orchards showed the sensitivity of AnnAGNPS to different temporal scales in modeling runoff and sediment yield under different management systems (Aguilar and Polo, 2005) and the model applicability to pre‐ dict runoff and sediment at event and monthly scales after calibration (Taguas et al., 2009). A calibration/validation exercise using a 10-year hydrological database in 53-km2 watershed in Ontario (Canada) highlighted that adjustments of the monthly curve number values and of the RUSLE parameters are relevant to improve the hydrology and sediment components of AnnAGNPS, especially during winter and early spring periods (Das et al., 2009). A good model performance was obtained in terms of runoff and erosion prediction after calibration/ validation processes in a 136-km2 agricultural watershed in south-central Kansas; total phos‐ phorus predictions were instead good only for the calibration period (Parajuli et al., 2009). Finally, a poor model performance in simulating agricultural pollution by nitrogen, phos‐ phorus and sediment was obtained in a 16.97-km2 watershed located in North Dakota (USA), mainly due to the large size of the study area and the high variability in land use and management practices (Lyndon et al., 2010).

Thus, the results of AnnAGNPS evaluations that have hitherto been carried out are general‐ ly promising. At the same time it can be noticed that model performance is variable and the boundary conditions under which the model may be successfully used for runoff and sedi‐ ment yield prediction have not been well defined.
