Environmental Engineering Reference
In-Depth Information
5
Accounting for Sediment
in Flood Risk Management
COLIN THORNE, NICK WALLERSTEIN, PHILIP SOAR,
ANDREWBROOKES,DUNCANWISHART,DAVIDBIEDENHARN,
STANFORD GIBSON, CHARLES LITTLE JR, DAVID MOONEY,
CHESTER C. WATSON, TONY GREEN, TOM COULTHARD
AND MARCO VAN DE WIEL
Abstract
reaches as sediment sources (eroding reaches),
pathways (dynamic equilibrium reaches) and sinks
(depositional reaches) and construct reach- and
catchment-scale budgets for stream power or sed-
iment movement. The more advanced models can
generate indicative data on rates of net erosion and
deposition in unstable reaches. All of the methods
and models have a role in the assessment, model-
ling and management of sediment-related flood
risk. The tools are also useful in developing an
understanding of long-stream connectivity in the
fluvial system, which is important to the function-
ing and management of the river as an ecosystem.
River sediment dynamics at the catchment scale
must be taken into account when managing flood
risk sustainably because the presence and move-
ment of sediment has important impacts both on
the capacity of the channel to convey floods and
the range and quality of habitats that it provides.
However, conventional sediment transport calcu-
lations performed at the cross-sectional or reach
scales cannot provide the information needed to
manage sediment at the system or catchment
scales. Recognizing this, a work package in Phase
1 of the Flood Risk Management Research Con-
sortium (FRMRC) assembled a toolbox of methods
and models capable of investigating broad-scale
sediment transfer through the river system. The
six approaches in the FRMRC Sediment Toolbox
are: (i) Stream Power Screening Tool; (ii) River
Energy Audit Scheme (REAS); (iii) Sediment Im-
pact Analysis Method, embedded in HEC-RAS
(HEC-RAS/SIAM); (iv) Hydrologic Engineering
Center, River Analysis System (HEC-RAS version
4.0); (v) iSIS Sediment; and (vi) Cellular Automa-
ton Evolutionary Slope and River Model (CAE-
SAR). The simpler tools may be used to classify
Background
Context
Historically, flood riskmanagement in theUKhas
seldom taken into account the erosion, transfer
and deposition of sediment, or the effects of flood
management on sediment dynamics in the fluvial
system (Environment Agency 1998). However,
schemes that disrupt sediment continuity or con-
nectivity tend to requireheavier andmore frequent
maintenance, either to prevent sedimentation
from compromising the design capacity of the
channel for flood conveyance, or to prevent dete-
rioration or failure of flood defence assets due to
fluvial erosion (HR Wallingford 2008). Also, the
