Watershed average slope length (ASL) is defined as the average distance measured along the main channel from the watershed outlet to the basin divide. It is an important parameter in a hydrologic model. Theoretically ASL is related to the calculation of lateral flow and routing timing, which eventually impacts simulation of the total surface runoff. SWAT (Soil and Water Assessment Tools) is a river basin scale model developed to predict the effects of management decisions on water, sediment, nutrient and pesticide yields with reasonable accuracy on lager, and ungauged river basins. The AVSWAT model, an integration of SWAT2005 and ArcView GIS 3.2, was applied in this paper to simulate monthly stream flow (1990-2009) of the Yingluoxia outlet of the 10 000 km2 upstream basin of the Heihe River basin (HRB). The simulation showed that ASLs calculated by the AVSWAT model were not consistent with the actual cases in the upstream basin of HRB. As a result, it led to an inaccurate simulation. To address this problem, a new approach has been adopted to correct ASL of each sub-basin. A regression equation, which reflects the relationship between average slope and average length, was established by measuring average slope of each sub-basin. Using the corrected slope lengths and the default parameter set of SWAT together with meteorological and hydrologic data from 1990 to 2009, Nash-Sutcliffe coefficient (NSE) of monthly runoff simulation is obviously improved to 0.75 in contrast with 0.60 with uncorrected slope lengths and same parameter set. Sensitivity analysis and an examination of CN2 parameter were also conducted to prove the applicability of this correcting method. The results showed that corrected slope lengths were more suitable for the studied mountainous basin and also verified its applicability of the adopted correction approach. Using the corrected ASLs, an error-trial optimization was used to optimize other parameters. The validation with daily runoff from 2000-2009 showed an NSE of up to 0.81, which suggested an acceptable simulation for the study basin. We concluded on basis of corrected slope lengths quite good simulation can be achieved by parameter optimization. Therefore, the approach to correct ASL is feasible in mountainous basin, and the corrected slope lengths have made the stream flow simulation better.
YU Wenjun, NAN Zhuotong, LI Shuo, LI Chenggang
. Average Slope Length Calculation and Runoff Simulation[J]. Journal of Geo-information Science, 2012
, 14(1)
: 41
-48
.
DOI: 10.3724/SP.J.1047.2012.00041
[1] Jayakrishnan R,Srinivasan R,Santhi C,et al. Advances in the application of the SWAT model for water resources management[J].Hydrological Processes,2005,19:749-762.DOI:10.1002/hyp.5264.
[2] Van Liew M W,Garbrecht J.Hydrologic simulation of the Little Washita River experimental watershed using SWAT[J].JAWRA Journal of the American Water Resources Association,2003,39(2):413-426.
[3] 宋艳华,马金辉.SWAT模型辅助下的生态恢复水文响应研究——以陇西黄土高原华家岭南河流域为例[J].生态学报,2008,28(2):636-644.
[4] 康杰伟,李硕.SWAT模型运行结构与组织研究[J].地球信息科学,2007,9(5):76-82.
[5] 刘昌明,李道峰,田英,等.基于DEM的分布式水文模型在大尺度流域应用研究[J].地理科学进展,2003,22(5):437-445,541-542.
[6] Luo Y,Marios S.Two-way coupling of unsaturated-saturated flow by integrating the SWAT and MODFLOW models with application in an irrigation district in arid region of West China[J].Journal of Arid Land,2011,137-164.
[7] Eckhardt K,Haverkamp S,Fohrer N,et al. SWAT-G,a version of SWAT99.2 modified for application to low mmountain range catchments [J].Physics and Chemistry of the Earth,2002,641-644.
[8] Ahl R S,Woods S W,Zuuring H R.Hydrologic calibration and validation of SWAT in a snow-dominated Rocky Mountain watershed,Montana,USA[J].Journal of the American Water Resources Associatio,2008,1411-1430.
[9] 王中根,刘昌明,黄友波.SWAT模型的原理、结构及应用研究[J].地理科学进展,2003, 29(1):79-86.
[10] 秦耀民,胥彦玲,李怀恩.基于SWAT模型的黑河流域不同土地利用情景的非点源污染研究[J].环境科学学报,2009,29(2):440-448.
[11] 黄清华,张万昌.SWAT分布式水文模型在黑河干流山区流域的改进及应用[J].南京林业大学学报(自然科学版),2004,28(2):22-26.
[12] 魏国,姜海,何俊仕.流域平均山坡长度的提取及其在SWAT模型中的应用[J].中国农村水利水电,2007,6:24-26.
[13] 李硕.GIS和遥感辅助下流域模拟的空间离散化与参数化研究与应用 .南京师范大学博士论文,2002.
[14] 胡兴林,畅俊杰,姚志宗,等.干旱半干旱地区水文预报模型研究及应用——以洮河流域为例[J].冰川冻土,2003,25(4):409-413.
[15] 李硕,孙波,曾志远,等.遥感、GIS辅助下流域空间离散化方法研究[J].土壤学报,2004,41(2):183-189.
[16] Lim K J,Kim J G.Development of SWAT ArcView GIS Patch II to reflect steep topography in Korea .Master.Kangwon,Korea:Kangwon National University,2007,1-56.
[17] Neitsch S L,Arnold J G,Kiniry J R,et al. Soil and water assessment tool user's manual,version 2000[M].Temple,Texas:Grassland,Soil and Water Research Laboratory,2002,1-781.