Sediment budget analysis

Method indicator
Bottom-Up	Hybrid	Top-Down
		YES

Summary of key issues:

Issue	Description
Description	Concept of overall sediment mass continuity within estuary system.
Temporal applicability	Any.
Spatial applicability	Any.
Links with other tools	Always useful as an aid to conceptual understanding.
Data sources	Bathymetric datasets (see HTA); Suspended sediment concentration measurements; Sea bed density; Fluvial discharge; Discharge measurements at the mouth of the estuary; Estimates of littoral drift made on the basis of standard equations or numerical models and wave data; Estimates of sediment transport made by numerical models.
Necessary software tools / skills	Understanding of sediment transport in estuaries; Geomorphological interpretation of output.
Typical analyses	As a conceptual aid to understanding how an estuarine system functions; As a method of quantifying a bulk flux or mass of sediment which cannot be identified by modelling or field measurement, e.g. residual net transport over long periods.
Limitations	It can be necessary to consider the mathematics of the method in detail to understand whether a particular analytical method can reliably be applied to a given estuary system.
Example applications	Humber Estuary; Mersey Estuary; Stour/Orwell System.

Introduction

A sediment budget is a balance of the sediment volume entering and exiting a particular section of the coast or an estuary. Sediment budget analysis consists of the evaluation of sediment fluxes, sources and sinks from different processes that give rise to additions and subtractions within a control volume (e.g. a section of coast or an estuary) in order to gain a better understanding of the estuary system. Control volumes on open coasts pertain to sections of a coast which form sediment cells and are controlled by cell boundaries which either inhibit or limit the amount of transport across the cell boundary. A source increases the quantity of material within the control volume and a sink reduces it and within the cell there may be point sources and sinks, such as tidal inlets, and line sources and sinks, such as movements on and off the beach.

An estuary provides a readily defined control volume, where point sources and sinks exist in the form of rivers, other terrestrial outfalls and the open sea. Line sources and sinks may be defined in terms of erosion from cliffs and transfers to or from saltmarshes, wetlands or other intertidal areas. The subtidal beds also needs consideration as an important source/sink as does material stored in suspension within the volume of water that moves back and forth under tidal action within the estuary.

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The Estuary Guide

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