Approaches toContinental Scale River Flow Routing byKwabena Oduro Asante

Dr David MaidmentDr James FamigliettiDr Francisco OliveraDr Randall CharbeneauDr Daene McKinney

AcknowledgementsDissertation Committee

National Science Foundation

EROS Data Center of the USGS GIS Hydro Research Group

Global Hydrology Group

Dissertation OutlineChapter 1: General Introduction

Chapter 2: Literature Review

Chapter 3: Data Development

Chapter 4: STS and HMS Methodology

Chapter 5: Model Applications

Chapter 6: Conclusions and Recommendations

MotivationThe changing scope of hydrologic problems Local scale to global scale Single phase to full hydrologic cycleSpatially lumped to spatially distributed

The limitations of current routing modelsLocal scale models untested at global scaleLack of integration of hydrologic cycle phasesScale dependence of existing large scale models

ObjectivesTo develop a database of hydrologic parameters to support continental scale runoff routing

To implement a continental scale runoff routing system for transferring water balance model outputs to ocean models

To examine the robustness of the modeling approach implemented as compared to a watershed based approach

Chapter 2:

Literature Review

Cell-to-CellWatershed BasedConceptual Models of a River BasinCTCHMSSource-to-SinkSTS

Translation with Incidental DispersionTranslation with Surrogate DispersionMethods of Characterizing FlowExample: Linear Reservoir RoutingExample: Cascade of Linear ReservoirsTranslation with Physically Based DispersionExample: Diffusion Wave RoutingSIQIQ

Chapter 3:

Data Development

to develop a GIS database to support large-scale surface water routing globally Study Objective 1

Terrain AnalysisIdentify Inland Catchments and insert in projected DEMLower Datum andProject DEMFill DEM and Compute Flow DirectionComputeFlow LengthCompute Flow AccumulationDelineate DrainageBasins

27 Major Inland Catchments

1500 Major Drainage Basins

GIS Hydro 99: Digital AtlasDigital Atlas of the World Water Balance www.crwr.utexas.edu

Preprocessing for theSource to sink (STS) modelDefine Sinksalong continentalmargin and withinInland CatchmentsDelineate DrainageBasins from Sink LocationsDefine Sources while preservingbasin boundariesas well as Ocean and Atmospheric modeling units1234Determinerouting parametersfor each Source fromFlow length and other Spatially distributed data

Linking to Ocean and WaterBalance ModelsSTS Modeling Units

Preprocessing for the Hydrologic Modeling System (HMS)Delineate StreamNetwork from Flow Accumulation Gridand define outletsat stream intersectionsDelineate Watershedsfrom outlet grid and Flow direction grid and convert to a vector coverageCompute stream and watershed parameters and connectivityCreate HMS basinfile detailing element properties and connectivity1234

Chapter 4:

Methodologyto implement a modeling framework which incorporates basin boundaries in a grid based model while maintaining computational efficiency by only performing routing at desired locations Study Objective 2

STS Modeling Assumptions The control volume is the flow path from a given source to its sink

The transfer of flow along the flow path is a linear process

The parameters of the transfer function are time invariant

STS Model Components

Impulse Distribution about Pure Translation Lag Time

Input Runoff from GCM (generated by Branstetter,M.)

Discharge at Continental Margin

HMS Modeling Assumptions Each hydrologic element has a unique control volume linked to the next downstream element

The transfer of flow along the flow path may be linear or non-linear

The parameters of the transfer function are time invariant

HMS Model Components

HMS Flow RoutingSubbasin Response by SCS Unit HydrographRiver Reach Response by Muskingum Routing with lag_time = max { (0.6 maxlagtime in minutes), 3.5 interval}with n = int (2 x K / 60) + 1Numerical stabilityPureTranslation

Chapter 5:

Model Applicationsto examine of the robustness of the source to sink approach as compared to the watershed based approach in continental scale applications Study Objective 3

The Application BasinsThe Nile BasinArea =3.25 million km2 Mean flow = 2,500 m3/sThe Congo BasinArea = 3.78 million km2Mean flow = 45 000 m3/s

STS Model RunsSTS Model of the Congo BasinSTS Model of the Nile Basin

Longitudinal Decomposability in STS2000 km1000 km1200 km800 km

Longitudinal Decomposability in STS !Cell 4Cell 3Cell 2Cell 1

Effect of STS Modeling Unit SizeSource size = 30(60 x 60 km)Source size = 10 (20 x 20 km)Source size = 5(10 x 10 km)

Effect of Spatial Resolution STS basin response for the Congo !

Effect of Temporal Resolution STS basin response for the Congo !

Effect of Spatial Distribution of V and D on STS basin response for the Nile

Effect of Spatial Distribution of Velocity STS basin response for the NileDistributed V is important !

Effect of Spatial Distribution of Dispersion STS basin response for the NileDistributed D is not critical !

Combined Effect of Velocity and Dispersion STS basin response for the NileDistributed V and D is best !

HMS Model RunsThe Nile BasinThe Congo Basin

Longitudinal Decomposability in HMSn = 4n = 5n = 6n = 7n = 8 reach length = 162,000 m flow velocity = 0.3 m/smuskingum K = 0.3

Longitudinal Decomposability in HMShigher n = less dispersion !

Effect of HMS Modeling Unit SizeStream Delineation Threshold of10,000 km2Stream Delineation Threshold of1,000 km2

Effect of Spatial Resolution HMS Basin Response for the CongoHMS is spatially scale dependent !

Effect of Temporal Resolution onHMS Congo Basin ResponseHigher routing interval = more dispersion

Comparing STS and HMSBasin ResponsesHMS Model of the Congo BasinSTS Model of the Congo Basin

Comparing STS and HMS Basin Responses Congo Basin, 1000 km2 thresholdresponses almost identical !

Comparing STS and HMS Basin Responses Congo Basin, 10000 km2 thresholdresponses at higher threshold not identical !

Comparing STS and HMS Basin Responses Nile Basin, Spatially Distributed V and D

Comparing STS and HMS Basin Responses for Non-uniform Velocity Case, Nile BasinSimilar responses result from a common grid of V and D !

Comparing Simulated Flows with Observed Data

Observed Flows after deducting Baseflow

Parameters Obtained by Method of Moments

Period1Period2Period3MeanVelocity, V in m0.1070.1100.1140.110Disp. Coef., D in m2/s3924730260105746

STSSimulatedandObserved flows

Routing Input with Mean Parameters(V = 0.110 m/s, D = 5746 m2/s)The Method of Momentsis suitable for estimatingV and D !

Comparing Observed flows with HMS Routed flows

HMSSimulatedandObserved flowsHMS can be used to describe the hydrology of a large basin !

Chapter 6:

Conclusions and Recommendations

ConclusionsGTOPO30 DEMs are sufficient for the delineation and parameterization continental scale hydrologic models but not for the determination of hydraulic parameters (V, D) STS models are suitable for continental scale routing and parameter determination because spatial and temporal scale have minimal effect on their response.

Watershed models are scale dependent with respect to both temporal and spatial scale and are therefore not suitable for global parameterization. However, they can sufficiently represent the hydrology of a large basin.

The method of moments is suitable for the determination of hydraulic routing parameters (V, D) from observed flow data.

RecommendationsImplement automated network calibration of Velocity and Dispersion coefficient for global parameter calibration

Undertake further testing of diffusion type cell to cell routing with a view to replacing the linear reservoir equation

Examine the effects of time varying velocities and dispersion coefficients

Implement nested source to sink models for reservoirs

Implement diffusion wave routing in watershed models

SummaryProcessed a Terrain Database to support Hydrologic Modeling globally Implemented a routing system for global runoff, allowing for interactions with land-atmospheric and ocean modelsDeveloped a continental scale HMS modelDeveloped a global STS model of the entire earthExamined the robustness of the STS and HMS models to changes in temporal and spatial modeling scale Compared both the STS and HMS models to observed flows