Rivers Flooding

GEOS 3310 Lecture Notes:Rivers and Flooding
Dr. T. Brikowski Fall 2011

file:riversFlooding.tex,v (1.24, October 14, 2011), printed October 13, 2011

Introduction

• USGS general introduction to rivers • USGS real-time streamflow data • online Physical Geography Textbook section on rivers and fluvial processes

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Overview
There are a few fundamental lessons to be learned about rivers: • Natural behavior: – two types: meandering and braided – meandering streams migrate laterally, threatening nearby structures (see animation ) – rivers generally steepest at their headwaters; therefore erosion concentrated there, floods come and go quickly – rivers generally shallowest at their mouths; therefore deposition concentrated there, floods come and go slowly • Human management 2

– floodplain regulation can minimize flood damage and impact at minimal cost – riverbed can be channelized when building the floodplain cannot be avoided

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The Nature of Rivers

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Drainage Basins

Figure 1: General features of drainage basins and streams. [Fig. 8.7, Keller, 2008]. 5

Important Definitions
• movement of water is measured in terms of discharge, i.e. volume time passing a given point • the Discharge Equation describes this, where discharge Q equals stream cross-sectional area width W times depth D times velocity V relationship Q = W ·D·V which is effectively equivalent to the saying “still waters run deep” • rivers generally end in alluvial fans when they emerge onto flat plains, or deltas where they emerge into water bodies (see Mississippi or Indus river deltas) 6

• stream sediment transport is made up of 3 main components (see animation ): – bed load moves along bottom by rolling, skipping. About 10% of total – suspended load silt and clay carried in the water. Usually 90% of total – dissolved load carried in chemical solution, e.g. salts

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Meandering Stream Pattern

Figure 2: Idealized diagram of a meandering stream, [Fig. 9.12, Keller, 2011]....