The World of GIS Hydro ‘98

1. The World of GIS Hydro ‘98 Presented by: David R. Maidment University of Texas at Austin

2. Synthesis of GIS and Modeling GIS Hydrologic Modeling Environmental description Process representation Input Data Model Results

3. Linking Data and Models Integrated Spatial Database GIS Hydro ‘98 Models Watershed Characterization Atmosphere & Soil Water Runoff & Routing Hydraulics Water Quality

4. Hydrologic Modeling Traditional approach Spatial Hydrology Process Representation Environmental Description Process-based Modeling Map-based Modeling

5. Spatial Hydrologic Modeling Concept Hydrologic simulation Time series data Users Real World Spatial hydrologic model Spatial data

6. Dealing with Time Variation Continuous time hourly, daily t Steady state mean annual t Seasonal monthly t Q I Single event t

7. Modeling Procedure I. Environmental description using a map Two tasks: II. Process representation using equations

8. Ten Step Procedure for Modeling 1. Study design  2. Terrain analysis  3. Land surface description  4. Subsurface description  5. Hydrologic data representation 6. Soil water balance 7. Water flow 8. Constituent transport 9. Impact of water utilization 10. Presentation of results Environmental description Process representation

9. Step 1. Study Design Objectivesof the study?  Range and subdivision of thespatial domain?  Duration and subdivision of thetime horizon? Variablesto be computed?

10. Space, Time, and Process Variables Number of: Spatial units = L Variables computed = M Time intervals = N Time Variables N Computational effort ~ LMN M Space LMN < 10,000,000 for execution within ArcView L

11. Time-Averaged Modeling Mean annual flow and transport on a raster grid Time Variables M L N=1 Space

12. Land and Water Interaction • Water Characterization • (water yield, flooding, groundwater, pollution, sediment) Land Characterization (Land use, Soils, Climate, Terrain) Relationships between land type and water characteristics

13. Adapt Water to the Land System • Water Characterization • (water yield,flooding, pollution, sediment) Land Characterization (Land use, Soils, Climate, Terrain) Non Point Source Pollution (mean annual flows and pollutant loads)

14. Adapt Land to the Water System • Water Characterization • (water yield,flooding, pollution, sediment) Land Characterization (Land use, Soils, Climate, Terrain) CRWR-PrePro (GIS Preprocessor for HEC-HMS flood hydrograph simulation)

15. CRWR-PrePro: HMS Preprocessor Geographic Data Schematic Diagram Increasing Scale  Increasing Complexity

16. Digital Elevation Model (DEM)

17. Raster-Vector Equivalence Vector representation as points, lines and areas Raster representation on a grid of DEM cells Vector Outlet Stream Watershed Raster

18. “Burning In” the Streams  Take a mapped stream network and a DEM Make a grid of the streams Raise the off-stream DEM cells by an arbitrary elevation increment  Produces "burned in" DEM streams = mapped streams = +

19. Eight-Direction Pour Point Model  Begin with an elevation grid  Flow in direction of steepest descent

20. 78 72 69 71 58 49 74 67 56 49 46 50 69 53 44 37 38 48 64 58 55 22 31 24 68 61 47 21 16 19 74 53 34 12 11 12 Flow Direction Grid Elevation Flow direction grid

21. Flow Direction • Water flows to one of its neighbor cells according to the direction of the steepest descent. • Flow direction takes one out of eight possible values.

22. Grid Network Implied network between cell centers Flow direction grid

23. 0 0 0 0 0 0 0 1 1 2 2 0 1 1 2 2 0 3 7 5 4 0 3 7 5 4 0 0 20 0 1 0 20 1 0 0 0 1 24 0 24 1 0 2 4 7 35 1 2 4 35 1 7 Flow Accumulation Grid Number of upstream cells Classification of flow accumulation Number of cells > 6 = stream 0 cells = watershed boundary

24. Flow Accumulation • Flow accumulation is an indirect way of measuring drainage areas (in units of grid cells).

25. Types of Outlets and Nodes Stream junction node Stream headwater node System outlet node User-defined node Sub-basin Stream

26. Stream Segmentation • Stream segments (links) are the sections of a stream channel connecting two successive junctions, a junction and an outlet, or a junction and the drainage divide.

27. Watershed Delineation • The drainage area of each stream segment is delineated.

28. Thousand-Million Rule What DEM cell size to use?  Cell size = Region area /1,000,000 What size watershed to delineate?  Watershed >1000cells

29. Application of Digital Elevation Models Watershed Area (km2) Typical Application Cell Size 1” (~ 30 m) 3” (~ 100 m) 15” (~ 500 m) 30” (~ 1 km) 3’ (~ 5 km) 5’ (~ 10km) 5 40 1000 4000 150,000 400,000 Urban watersheds Rural watersheds River basins, States Nations Continental Global

30. Raster to Vector Conversion • Streams and watersheds are converted from raster to vector format.

31. Dissolving Spurious Polygons • Cells connected to the main watershed polygon through a corner are defined as a separate polygon (spurious polygon). • These polygons are dissolved into the main polygon.

32. Identification of the longest flow-path Slope and length of the longest flow-path Lag-timeSCS Unit Hydrograph Watershed Parameters Flow length upstream and downstream AverageCurve Number

33. Flow-Length Function in ArcView  distance downstream to outlet  distance to upstream divide

34. Flow Length Downstream to the Watershed Outlet

35. Flow Length Upstream to the Watershed Divide

36. Longest Flow-Path Total flow length = upstream length + downstream length

37. V11 V12 V13 V14 V15 V16 V21 V22 V23 V24 V25 V26 V31 V32 V33 V34 V35 V36 V41 V42 V43 V44 V45 V46 V51 V52 V53 V54 V55 V56 V61 V62 V63 V64 V65 V66 Velocity Field Velocity magnitude Velocity direction V = aSb S = slope a,b = land cover coefficients

38. 1 Time = Distance x Velocity Flow Time Computation  time to outlet (weighted flow length)

39. Isolation of a Sub-System

40. HMS Basin File Connection to HEC-HMS HMS Schematic Parameter Transfer Ferdi’s code

41. Upper Mississippi Flood Study

42. Streams and Subwatersheds 162 subwatersheds each with a USGS gage at the outlet defined using 15” (500m) DEM Rivers defined by EPA River Reach File 1 (RF1)

43. Inlets CRWR-Prepro Schematic Network Mississippi River Missouri River Outlet (Mississippi R. at Thebes, Ill)

44. HEC-Hydrologic Modeling System HEC-HMS Model Schematic CRWR-PrePro HMS Basin file

45. Adapt Water to the Land System • Water Characterization • (water yield,flooding, pollution, sediment) Land Characterization (Land use, Soils, Climate, Terrain) Non Point Source Pollution (mean annual flows and pollutant loads)

46. Water Land Possible Land-Water Transform Coefficients

47. Map-Based Surface Water Runoff Estimating the surface water yield by using a rainfall-runoff function Runoff, Q (mm/yr) Q P Runoff Coefficient C = Q/P Accumulated Runoff (cfs) Precipitation, P (mm/yr)

48. Water Quality: Pollution Loading Module Load [Mass/Time]=Runoff [Vol/Time]x Concentration [Mass/Vol] Precip. Runoff DEM LandUse Accumulated Load EMC Table Load Concentration

49. Expected Mean Concentration Land Use EMC Table derived from USGS water quality monitoring sites

50. Water Quality: Land Surface -Water Body Connection Bay Water Quality Total Constituent Loads Input for Water Quality Model