Dvances Geographic Information Systems - Assignment Example

dvаnсеd Gеоgrарhiс Infоrmаtiоn Systems Your name Name of Assignment 16th December , 2016 Table of Contents Auxilliary Data Generation 2 River extraction 3 Basins generation 6 Specific Watershed Delineation 7 Auxilliary Data Generation Using DEM one can extract contours and in this case will be extract the 50 meter contours. This will be done through the following procedure; A raster file is created to cover the data for mapping. A copy of the data file/raster file is made without changing the current file. This copy will have all files used appended The second step involves creation of contours using contour tool. This done by opening Contour tool and chooses interval which is in this case 50m. The scale is selected in this step. Then data is exported to mapping vicinity The third step is where the contours are checked against topographic maps available to ensure for consistency. To obtain these contours a correct Z factor will be applied. This step involves the labeling and displaying of the contours. This done by adding INTERVAL and “CONT_TXT” as well as calculating Contour fields. This step involves selecting and eliminating tiny contours This step involves smoothening of contour lines and this is done using Smooth Line tool. Errors in the measurement of topographic data can be minimized by quality control of the survey and are generally within acceptable tolerances. However, gross errors do sometimes occur and these need to be eliminated either by quality control procedures at the data input stage. The last step is differentiating sinks and hills within the contours. This follows smoothing of contours. River extraction The creation of DEM creates from the current by elimination sinks. DEM with no sinks ensures that accuracy is improved. There was no procedure for elimination sinks identified for the for emanation. There were no topographical maps useful for the area under consideration without sinks there we have to make them. Therefore we consider small scale, the largest being the 1:600,000. After creating a flow direction raster from DEM with the filled sinks, appears to be southeast direction. The chosen pixels need to be representative of the river reach. Thus between cross-sections there should not be any large changes in cross-section. Also, the cross-sections should be drawn normal to the general flow direction. From this raster calculate the flow accumulation and use a conditional statement in order to extract the hydrographic network. After making adjustments in the data for the variation effects, it is relatively easy to sort out changes caused by other factors in the data. If these adjustments are not made, then identifying the differences caused by non-seasonal factors becomes nearly impossible. The extracted hydrographic network Errors in the measurement of data can be minimized by quality control of the survey and are generally within acceptable tolerances. However, gross errors do sometimes occur and these need to be eliminated either by quality control procedures at the data input stage (for example by plotting all the cross-sections on the computer screen) or during the model calibration procedure. Errors in the hydrological data are not so easy to eliminate and may, therefore, need to be catered for by a sensitivity analysis. In the entire observed hydrographic network, it flow direction is east direction. This point, when joined to the point of rise of the hydrograph, marked the base flow separation. The success of the model in the catchment showed that the model can be easily extrapolated into neighboring catchments for estimating runoff volumes. However, the model requires some rainfall-runoff data for parameter estimation. The use of the method of moments in the Nash model for parameter estimation was found satisfactory in the area while in the Lagan catchment geomorphic relationships were found superior. Although the former required some data, the latter enabled the model to be applied in ungauged catchments. The kinematic wave model performed well in the area but less satisfactorily in the area. From the raster of the rivers and the flow direction raster create a shapefile of these rivers. One begins with opening Arc Hydro toolbar where attribute tool of accumulated is selected The Layer with NextDownID is selected. Select feature called Catchment and then NextDownID Catchment will also be selected as Source Feature Layer Then volRainfall is selected as Source Field. The sum is done using accumulation Type The accuracy of the individual parameter values may not be a requirement to reasonable performance of the model in simulating floods, reflecting the equifinality phenomenon. The inexactness of parameter values will have negative implication of the results and its interpretation especially when it comes to catchment behavior such as predicting the effects of changes in climate. Logically, the objective function adopted to calibrate a model should be directly reflected in the primary model efficiency index and clearly that index should directly reflect the primary requirement(s) of the modeling task. The flow model which usually relies on time function is used to calculate flow conditions and is useful when the river has many tributaries and subsidiaries flowing either across countries or across areas where many parameters are affected by these changes. These models are used to determine the amount of water that is expected in a river at a specific time. This means forecasting river flows during flooding will be affected by other conditions which are difficult to forecast thus making simulations and calculations have less accuracy. They also rely on historical data which does not take into consideration the changes in weather conditions. The models usually use calibration in modeling process because of the difficulty of measuring the parameter that is used with the intention of ensuring that the process maintains some accuracy. In predicting future flood river flows, is challenging when it comes to environmental changes since it is not easy to predict the course the climate takes. The models can estimate or quantify the impact of climate or land use in predicting flood river flows but it is inaccurate or uncertain. Another problem with models, they use poorly measured catchments which ends up giving wrong or inaccurate results. Barriers affecting the ability of gauging catchment areas should be understood and eliminated to improve the data results. There should be also proper strategies that will help reduce errors during analysis or help in diagnosing the error as well as show the uncertainty in the data used. There is also erroneous representation of relationship between the runoff and the controlling input variables such as assuming linearity when it is not linear system. One may also assume that snow melt has no effect while it has. Basins generation The first step is to use DEM to create Direction flow and Accumulated flow which has already done in form of FlowDir1 and FlowAcc1 The next stage involves creating shapefile by using file menu to choose PourPoint1. This will set an empty shapefile. Then points of the are adjusted in the map. Specific Watershed Delineation This is done using the following procedure to change to into shapefile for using The area of this watershed in square kilometers IS 2750km2. The following is the map of the watershed with the outlet point, the rivers and the contours in scale 1:100,000. Read More