hydrologic topology

Hydrologic Topology Francisco Olivera, Ph.D., P.E. – Assistant Professor (folivera@civilmail.tamu.edu)

Srikanth Koka – Graduate Research Assistant (srikanth@tamu.edu) Texas A&M University – Department of Civil Engineering - College Station, Texas

Mississippi River System

Mean Annual Precipitation

Downstream Flow Length

Weighted Drainage Area

Upstream Trace

Longest Flow Path

Overview

Due to the inherent spatial complexity of large hydrologic systems, for modeling purposes, rather than applying lumped models to represent entire basins, it is better to subdivide them into elementary flow elements organized as networks by virtue of their topologic relations. Likewise, each element should have different hydrologic properties to account for the terrain spatial variability and different hydrologic behavior to account for the different flow processes.

Hydrologic topology is the relation of the flow elements of a system to one another, so that each of them "knows" which other elements are upstream and which are downstream. Establishing the hydrologic topology is fundamental for flow routing as well as for tracking constituent particles transported by water.

Use of vector data, as opposed to raster data, has the advantage that each element represents a real-world flow element and, consequently, sets a better ground for physically-based modeling, not to mention that overall it is more accurate and better suited for modeling large study areas.

252-526 mm/year

527-801 mm/year

802 – 1076 mm/year

1077-1351 mm/year

1352-1626 mm/year

0-1000 Km

1000-2000 Km 2000-3000 Km 3000-4000 Km 4000-5242 Km

CityName

UpstreamFlow

Length(Km)

DownstreamFlow

Length(Km)

Drainage Area

(Km2)

AnnualMeanFlow

(m3/sec)

2013

2662

1819

3627

5337

410,932Little Rock

Omaha

Paducah

St.Louis

New Orleans

974

2675

1496

1710

2013

824,543

513,680

1,790,860

3,196,680

9,881

12,433

20,090

37,469

85,914

1,885(2)

1,274(2)

3715(3)

6,601(2)

16,772(4)

0 – 10 106 mm Km2/year10 – 100 106 mm Km2/year

100 – 500 106 mm Km2/year

500 – 1000 106 mm Km2/year

1000 – 2711 106 mm Km2/year

Network Topologic and Geometric Parameters

PotentialMeanFlow

(m3/sec)(1)

(1) Potential Mean Flow (m3/sec) = Weighted Drainage Area (mm Km2/year) , (2) Value for 1999, (3) Value for 2000, (4) Value for 1995

Mississippi River Climate & Hydrology ConferenceMay 13 – 17, 2002New Orleans, LA

31,555

Hydrologic Topology GIS Tools

For every point of the network, the tools:

•Identify upstream and downstream streams and watersheds.

•Determine upstream flow length and weighted upstream flow length to the farthest headwater.

•Determine downstream flow length and weighted downstream flow length to the outlet.

•Determine drainage area and weighted drainage area.

•Trace upstream and downstream for user-defined points of the network.

•Identify the longest flow path of the system.