The Quantitative Planning Of Riparian Vegetation Buffer Strip In Plain River Network

Riparian vegetation buffer strip refers to the buffer area along the river. Its function is to prevent nutrients, sediments, organic matter, pesticide and other pollution from entering the river system brought by sloping surface run-off, waste water release, groundwater and deep groundwater flow. That is why it has always been an important instrument in river protection. It plays an important role in maintaining the health of water ecosystem, and has been paid attention by not only the academic circles, but also the construction and administration departments.How to plan an effective riparian vegetation buffer strip for water quality conservation? Before answering this question, we need to dress the following questions:(1) How are we to deal with the spatial distribution of the riparian vegetation buffer strip width? (2) How are we to determine the riparian vegetation buffer strip width? (3) On the basis of the width, how are we to regard the species and composition of the vegetation?This study, in the first place, reviewed and compared relative studies at home and abroad. Next, the plain river network area is characterized by its plain topography, and rapid urbanization. Based on GIS software, a set of suitable procedure and methodology for the planning of riparian vegetation buffer strip is established. Meanwhile, the reference conditions are set up, via extensive field investigation on the riparian vegetation species, and data analysis. Thirdly, take Shanghai Dishui Lake as an example, using "3S" technologies; the special database is built up. Fourthly, Quantitative model non-point source pollution loads and runoff routes, and define the width, pattern, vegetation species and quantity of the buffer. All these lead to the accomplishment of the quantitative planning of regional riparian vegetation buffer strip. The results and conclusions are as follows:Procedure and methodology:(1) The planning of riparian vegetation buffer strip shall be studied under the framework of "watershed division-measurement on non-point resource pollution load and rainfall path-establishment of community reference condition-riparian planning" The planning mainly includes two aspects. Firstly, locate and gain the breadth of the buffer based on non-point source pollution load and runoff pathway. Secondly, according to the established riparian vegetation reference condition, and with the modeling of special location and width, define the species and composition of the vegetation.(2) Establishment of the reference condition:The reference condition is set up, via extensive field investigation on the riparian vegetation species, and data analysis.(3) Watershed division:In plain river network, it is difficult to divide a watershed because of the disturbance of rainfall path caused by closed river network structure, plain topology, water conservancy facility regulation and intensive human activities. Aiming at such condition, this study, divides the watershed through two angles, that is, within the river network and between the two river networks. In polygonal river networks areas, watershed delineation is the first step in many hydrological projects. In rapidly urbanized plain river network areas, some landcover features can't be shown in DEM, which caused errors in drainage patterns due to low density of elevation value. Poor landcover features representation in DEM has frequently caused the error of drainage patterns due to the lower precision of the height source or elevation values. To avoid these problems, a new approach, using the digital landcover features (e.g. roads, buildings, ponds, and pipe drainage systems) as ancillary data are added into DEM, has been developed. To avoid detrimental changes in DEM, distance transformation concepts are used to determine the elevation offset distribution in the plain river network areas. The new approach supports the application in small-scaled plain river network areas by modifying two newly added scenes (landcover features are added in DEM and landcover features are burned in DEM). As for inter-sectional river network areas, considering the influence to water volume and direction led by the regulation of dams or other water conservancy facilities, make clear the outlet of the relative network and finish the division work.(4) Measurement on non-point resource pollution load and rainfall path:This study borrowed the modified SCS model for reference, to calculate the runoff yield based on the data of rainfall-runoff was also given. In the same way as the calculation of runoff yield, this study borrowed PLOAD and EMC (event mean concentration) for reference, to calculate the total non-point source pollution loads of the watershed at one single rainfall event. The pollution load of the buffer runoff is then derived. The modeling of the pollution flow path is further done in ArcGIS Hydrology tools.(5) Planning of riparian vegetation buffer strip:The study applied a width variable calculation method. Based on time models and hydrology models created by different researchers targeting protection of riparian, with comprehensive consideration of physical and chemical properties of soil, topology, landcover, and other special environmental factors, calculate the variable width of the riparian. On the basis of extensive investigation, the riparian vegetation species on different habitats are defined. The reference indicators and frames are separately created based on all kinds of vegetation types. These laid a solid foundation for the species selection and community construction of the riparian.A case study in Lingang:(1) Establishment of reference condition for riparian vegetation community:Based on extensive field investigation on the riparian vegetation community in Shanghai, eight habitats are gained using the cluster analysis of SPSS. The investigation data of riparian vegetation under eight habitat conditions are analyzed statistically. Reference values of vegetation species, richness indicator, diversity indicators, and ratio of local species, vegetation coverage and the number of community vertical structures are defined under different vegetation types.(2) Watershed delineation:The analysis of sluices at each outlet within the watershed show that, during the year, the on and off status of each sluice changes with the change of water level of inner lakes. The flow direction of the river network varies periodically. The Dishui Lake watershed is a dynamic area. It alters along with the outlet, is quite different from the traditional one. There are three scenarios about the watershed area. During the non-diversion period, it is the smallest, covering an area of 76.15 km2. Such watershed lasts the longest, up to 282d. When Dishui Lake is drawing water from other rivers, the area becomes the largest, of 233.5 km2, lasting for 80d. Between the two circumstances, is the middle one with an area of 92.29 km2, and will last for only 3d.(3) Measurement on non-point resource pollution load and rainfall path:In the aspect of the special distribution of non-point source pollution in the watershed, regions producing NH3-N, TN, TP and TSS mainly concentrate at the north-east and the west of Dishui Lake. The non-point source pollution in the north-east is mostly centralized in network No.2. However, the pollution in the west scatters, distributes in every block, and centralized in the sole of every block. The analysis shows that these regions are mainly paddy fields and dry lands in land use. The study proves that agriculture is the main cause of non-point source pollution through modeling.The analysis on the non-point source pollution release routes shows that NH3-N, TN, TP and TSS are mainly following the route of B1 "buffer runoff-ditch-1st class stream", and then goes to B2"buffer runoff-ditch-2nd class stream" and A 1 "buffer runoff-1st class stream". These three routes account for over 70% of the total non-point source pollution release volume.(4) Planning of riparian vegetation buffer strip:Two profiles are separately set, based on the current situation of the landuse of both sides of the lake, and the simulation situation as woodland. An analysis was carried out to compare the riparian buffer width and location under these two profiles. In planning profile No.1, integrating the simulating results from both time model and hydrology model, it shows that, riparian buffer width ranges from 9 m to 74.5 m. Among that, riparian buffer width mainly ranges from 17.1 m to 42.4 m, In planning profile No.2, integrating the simulating results from both time model and hydrology model, it shows that, riparian buffer width ranges from 9 m to 56.4 m. Among that, riparian buffer width mainly ranges from 13.3 m to 29.8 m. On the foundation of such, two sets of riparian vegetation species and specific community parameters are chosen based on the site condition around the river and the frame of reference condition.The innovations in the dissertation are as bellow:(1) Based on previous study results made by other researchers, a framework and a set of procedure of the planning of riparian vegetation buffer strip are addressed, and the techniques and the methodology are established.(2) Based on previous study results on establishment of reference condition, a procedure of the establishment of reference condition is discussed and a set of reference condition of riparian vegetation buffer strip for Shanghai is established.(3) Automated watershed delineation from DEM is the key step when conducting any spatially distributed hydrological modelling. For rapidly urbanized flat area, it fails to provide a realistic drainage structures and watershed boundary from conventional DEM processing methods. A new method was proposed for watershed delineation in urbanized plain river network.