Characterization of Hydrological Networks and Surfaces Theory and Tools

Characterization of Hydrological Networks and Surfaces Objectives 1. Explore basic tools (Spatial Analyst) Explore a DEM Prepare/ correct for new analysis Flow Direction and Accumulation 2. Convert data type (Spatial Analyst and Conversion) Identify and assign river orders 3. Conclude and discuss hydrological characterization Delineate watersheds Discuss the quality of analysis 4. Apply concepts of hydrological analysis to surface analysis Slope and Hillshade

Terms sinks flow river, stream order basin, watershed slope hillshade

Tools Sink Fill Flow direction Flow accumulation Set Null Stream Link Stream Order Stream to feature Select by Location Basin Slope Hillshade Objectives …

Start with the DEM DEM resolution of approximately 1 km O 1

Flow direction To show the DEM where water flows, define flow direction for each cell. –8 possibilities: N, S, E, O, NE, NO, SE, SO O 1

Fill in the false sinks O 1

Sinks These cells must be filled O 1

Flow Accumulation Gives us an idea of the geometry of rivers and streams ArcGIS Desktop Help Calculating flow accumulation. Hydrology (Spatial Analysis). webhelp.esri.com O 1

Rivers and Pour Points What is and is not a river? –Process of trial and error / guess and check River connections and orders Specialized raster to vector conversion –Assign IDs to each river O 2

Set Null Tool that converts values defined as “null” or “NoData” if the condition is true, e.g., if (VALUE_Facc < 500) then VALUE_salida = NoData else VALUE_salida = 1 Yes, there is a difference between “0” and “NoData” O 2

The Difference Between “0” and “NoData” O 2

0101 NoData 1 2 O 2

Set Null Use this tool to eliminate all the cells that are not rivers and save only the cells that do represent rivers Process of trial and error –the magic value differs in each situation depending on many variables O 2

River connectivity Connect the rivers in order to obtain an actual drainage network, not only a visual representation of the rivers O 2

River Order Assign an order to each segment of each river Why? –Once the order is identified, some characteristics can be inferred E.g., First order rivers are more susceptible to nonpoint source pollution and benefit greatly from riparian forests O 2

River Order Two Methodologies: Strahler and Shreve from ArcGIS Desktop Help O 2

Rivers: From Raster to Vector Various methods exist to convert between raster and vector in GIS Use a tool designed specifically for river conversion O 2

What is a basin or watershed?

Watersheds / Basins System composed by the interrelations of social, economic, demographic, and biophysical subsystems. Planning and evaluation unit Management includes anthropogenic focus as well as disaster prevention ¹ Trejos, Noel Presentación, “Retos y perspectivas del manejo integrado de cuencas hidrográficas para la mitigación de impactos del cambio climático”

Watersheds / Basins “Political divide” –Basin limits –Rivers

Post Flood Changes: Río Sixaola ASTER SPOT Analysis in the context of The Visualization and Monitoring System (SERVIR))

Delineating Watersheds / Basins Delineation quality –Scale and resolution –Basin, watershed, catchment Compare the results of flow accumulation using inputs with different spatial resolution O 3

Surface Characterization Slope Hillshade

Slope y trigonometry

Hillshade Provides a 3D effect Almost never used alone–use semi-transparently superimposed on another layer