Estuary model

Estuaries are a key part of the environment controlling the fate of nanomaterials. The mixing of freshwater and seawater - coupled with the tidal movements - creates a rapidly changing environment within the water column in terms of the water flow, salinity (salt concentration) and suspended sediment concentrations. Within the gridded NanoFASE water-soil-organism model, estuaries are split up into a number of linked "estuary  reaches", the conceptual model for which is shown below. Each reach has a bed sediment, which is documented separately.

Conceptual  model  of  estuary  reaches  and  their  bed  sediments  within  the  NanoFASE  water-soil-organism model

The  processes  transferring  water,  sediment  and/or  nanomaterial  between  the  reaches  that  make  up  an  estuary  are  the  same  as  those  listed  for  the  river  reach  model. The  main  modelling  difference  lies  in  the  treatment  of  advection  (the  bulk  flow  of  the  water  upstream  or  downstream),  because  there  is  a  need  to  simulate  tide-influenced  movement  of  water  upstream  and  downstream.

 Advection  is  modelled  by  computing  the  volume  of  water  within  each  reach  every  hour,  and  using  this  to  compute  the  movement  of  water  into  and  out  of  each  estuary  reach  on  each  time  step.  The  volume  of  water  in  each  reach  is  computed  using  the  theory  of  tidal  harmonics,  which  allows  the  change  in  water  depth  at  a  point  in  an  estuary  over  time  to  be  calculated  by  considering  the  separate  influences  of  the  sun,  moon  and  tidal  friction  on  the  depth  of  the  tide  over  time  (see  diagram). Nanomaterials within each reach can undergo identical transformations to those listed for the river reach model.

Example of computed water height (m) due to tidal forcing, for one spring-neap tide cycle


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Read also


NanoFASE Report D2.1 Specification for the NanoFASE model
NanoFASE Report D2.2 Spatial transport framework 

Hardisty,  J.  (2007).  Estuaries:  Monitoring  and  Modeling  the  Physical System.  Blackwell,  Malden,  MA,  U.S.A. 




  Sam Harrison

  Centre for Ecology and Hydrology (CEH)