• No results found

Effects of spatial vegetation roughness parameterization on 2D flow characteristics

N/A
N/A
Protected

Academic year: 2022

Share "Effects of spatial vegetation roughness parameterization on 2D flow characteristics"

Copied!
1
0
0

Bezig met laden.... (Bekijk nu de volledige tekst)

Hele tekst

(1)

Data processing

The study area is located in the Gamerensche Waard (GW) floodplain section in the Netherlands. Both methods enable driving the rough model of Baptist (2005):

where Cris the composite Chézy coefficient representing roughness of a vegetated bed (m1/2s-1), Cbis the Chézy roughness of the bed (m1/2s-1), g is the gravitational acceleration (ms-2), Cdis the drag coefficient for vegetation (-), Dvis the vertical vegetation density (the projected plant area in the direction of the flow per unit volume, m-1) and h is the water depth (m), Hvis the vegetation height (m) and is the Von Kármàn constant (0.4)

Model 1: The ecotope map converted to model input, albeit at the expense of spatial detail.

Effects of spatial vegetation roughness parameterization on 2D flow characteristics

Effects of spatial vegetation roughness parameterization on 2D flow characteristics

M.W. Straatsma, M.J. Baptist

a Utrecht University, Faculty of Geosciences, Department of Physical Geography, PO Box 80115, 3508 TC, Utrecht, The Netherlands, m.straatsma@geo.uu.nl. bDelft University of Technology, Faculty of Civil Engineering and Geosciences, Water Resources Section, PO Box 5048, 2600 GA, Delft, The Netherlands, now at IMARES Texel

M.W. Straatsma, M.J. Baptist

a Utrecht University, Faculty of Geosciences, Department of Physical Geography, PO Box 80115, 3508 TC, Utrecht, The Netherlands, m.straatsma@geo.uu.nl. bDelft University of Technology, Faculty of Civil Engineering and Geosciences, Water Resources Section, PO Box 5048, 2600 GA, Delft, The Netherlands, now at IMARES Texel

Introduction

Operational river management requires regular updates of roughness maps to drive the hydrodynamic models that predict peak water levels. Our aim is to compare two methods to map floodplain surface characteristics that are relevant for hydrodynamic modeling: (1) the Dutch ecotope approach based on the manual classification of aerial photographs, which lacks detail and repeatability and (2) a new semi-automatic high-resolution method based on the data fusion of airborne multispectral and lidar (Light Detection and Ranging) data. The effects on 2D flow patterns and water levels within a river and floodplain segment are assessed using the Delft3D

hydrodynamic model.

Introduction

Operational river management requires regular updates of roughness maps to drive the hydrodynamic models that predict peak water levels. Our aim is to compare two methods to map floodplain surface characteristics that are relevant for hydrodynamic modeling: (1) the Dutch ecotope approach based on the manual classification of aerial photographs, which lacks detail and repeatability and (2) a new semi-automatic high-resolution method based on the data fusion of airborne multispectral and lidar (Light Detection and Ranging) data. The effects on 2D flow patterns and water levels within a river and floodplain segment are assessed using the Delft3D

hydrodynamic model.

Model results for the GW floodplain section a) Chézy C roughness values (m1/2/s) based on model 1, b) difference in Chézy C roughness values (m1/2/s) between model 2 and model 1, c) magnitude of flow velocity (m/s), d) difference in flow velocity (m/s) between model 2 and model 1, and e) difference in water level (m) between model 2 and model 1.

Modelling results

Model 2 generates overall a lower roughness, and hence higher flow velocities. Nonetheless, locally the reverse is found. Differences in water level are limited to 1.5 cm. Calibration showed that the new method gave better estimates of the side channel discharge in two out of three cases.

Conclusions

This study shows that:

• The new method provides much more detail in model input in a repeatable way.

• The disaggregation of floodplain roughness leads to significantly different flow patterns, which is of value for morphodynamic models of side channels.

• High quality hydrodynamic field measurements are required to quantitatively assess the different error contributions.

a) Lidar raw data represents

• ground surface

• vegetation

• man made structures like power poles

b) CASI multispectral data.

Model 2

Classified land cover Individual trees

High res. vegetation structure

Standard Herbaceous Model 1 Ecotope roughness map

Positive values: Model 2 has lower roughness

High flow velocities through the side channels

Positive values: Model 2 has higher flow velocities, significant differences

Small differences in water level

Model 2:

• Segmetation into image objects and classification.

• Extraction of vegetation height and density for forest and herbaceous vegetation from lidar data

• Individual trees were delineated.

Referenties

GERELATEERDE DOCUMENTEN

Geen van de auteurs van twaalf meet- kunde-boeken, bestemd voor de le klasse v.h.m.o., die in mijn bezit zijn en uitgegeven rond 1960 (ongeveer 25 verschillende methoden waren er

In Westmaas werd alleen Boxer gespoten op 11 oktober en kon de bespuiting met middel G niet worden uitgevoerd, omdat het gewas na de winter niet meer terugkwam.. In Oostwold

The tautomerism could be responsible for the peak asymmetry, using the columns described for mass spectrometry, or peak broadening, as observed when SCOT OV-275 columns were

Hypothesis 3 stated that the relationship between social category-based faultlines in terms of strength and distance and team performance is moderated by a climate for inclusion

It combines existing ideas in literature with some new contributions: (1) a refined pixel-based distortion measure for each individual blocking artifact in relation to its

Due to the positive relationship between a two-tier board model and disclosure score plus the positive, significant, relationship between the presence of a supervisory board and

The analysis of existing literature on knowledge management in both the public and private sector has developed the argument that public institution characteristics

Het opspuiten van het zand gaat gepaard met grote krachten en soms transport door metalen buizen over aanzienlijke afstand, en dat laat helaas zijn sporen na op de meeste fossielen: