The Runoff Compensatory Effects Of The Vegetation Restoration In The Beiluo River Catchment

To control the severe soil erosion, a great number of soil and water conservationmeasures and Grain for Green project have been implemented in the studied region especiallyfrom the1970s. This paper analyzed the temporal and spatial variation of vegetation coverageon the Beiluo River by using the data from different sources. The trend and periodic of thetotal runoff and base flow of the different geographical types was analyzed by conducting therunoff separation for measured daily hydrological data. The response of total runoff to theregions with vegetation restoration and compensatory effects of the base flow were alsoanalyzed which had the significance of practical guidance and reference for ecologicalconstruction and rational using and planning of water resources. The results showed that:(1) During1987-2010, the vegetation cover of Beiluo River catchment generally showedincreasing trends ranging from41.12%to50.13%, it was obvious in Hilly and Gully Regionand Hilly-gully Region of Tableland and increased from18.40%and33.18%in1987to36%and54%in2010respectively. In the Forest Region and Terrace Plain Region, it was notobvious.(2) Over the five decades, the annual runoff in Hilly and Gully Regions, Hilly-gullyRegions of Tableland and Terrace Plain Region obviously decreased, however the runoff ofthe Forest Region was more stable. By comparing the variation of hydrological trends of high,media and low flow in different landforms types, the result implied that it was the forest coverand vegetation restoration, rather than the landform, that controlled the runoff trend on theregional scale.(3) The annual base flow had a significantly negative trend in Hilly and Gully Regionand it manifested inconsiderable decreasing tendency in other landforms types. The Pettitt’stest indicated that it had no obvious change points. The annual distribution of base flowshowed the double peak type, but the peak value of the non-forest areas occurred in Marchand August, the forest area’s value lately occurred in April and September. The unevencoefficient of annual distribution in the Hilly and Gully Region was the biggest while theTerrace Plain Region’s was the smallest and the annual distributions of each landform type were gradually homogenized by times.(4)The compensatory effects of vegetation restoration played a significant role in theHilly and Gully Region. The tendency of variation of the total runoff and base flow hadquadratic non-linear decreasing; the decrease extent of total runoff was bigger than base flow,the base flow index increased following years. The base flow index increased about0.066ifthe vegetation coverage has increased about10%. The ground water regression coefficientwas increased following the increase of vegetation coverage. The results indicated that theimpacts of vegetation restoration on the proportions of the runoff components can beconducted by enhancing the extent of ground water regression and increasing the basic flowindex.