standing water is extremely slow; the flow 

 rate of water through soil is restricted 

 through low permeability; and dissolved 

 oxygen in soil water is subject to biochemical 

 oxygen demand. 



Intragravel Oxygen Balance 



At any instant, a given volume of spawning 

 gravel may be assumed to be in a steady state 

 with regard to supply and removal of dis- 

 solved oxygen; that is, dissolved oxygen is 

 supplied and removed at a constant rate. 

 Intragravel dissolved oxygen sources are 

 stream water and ground water having high 

 dissolved oxygen content. Depletion is a re- 

 sult of biochemical oxygen demand and dilu- 

 tion with ground water having low dissolved 

 oxygen content. Periphyton on and near the 

 gravel surface also has an influence on oxygen 

 balance, producing oxygen in the presence of 

 sunlight and consuming oxygen during periods 

 of darkness. Its influence on intragravel dis- 

 solved oxygen levels is poorly understood. 



Consider the ideal intragravel system pic- 

 tured in figure 7. 



Here interchange (i), ground water (g), and 

 intragravel flow (a) are supplying dissolved 

 oxygen at different concentrations and flow 

 rates. Oxygen is leaving the system through 

 intragravel flow (f), and biochemical oxygen 

 demand (B), (and upwelling if Wi is negative). 



A complete oxygen balance over an intra- 

 gravel volume may be expressed as: 



WiCi + WaCa + WgCg = WfCf + VB 



Where 



W is the volumetric flow rate, 

 3 

 m. wa_ter. ^ ^^^ dissolved oxygen 



sec. 



concentration. 



g. 



oxygen 



; V the 

 cm. "* water 



volume of gravel, cm. ; and, B the 

 biochemical oxygen demand, 



S: oxygen 



cm. 3 gravel sec. ' 



By careful measurements, stream profiles 

 and gravel permeabilities (Pollard, 1955) may 



Wi-Cl 



OO OO OOOOOOOOOOOOOOO 



Wo- Co 



Wf.Cf 



Wg.Cg 



Figure 7. --Intragravel oxygen balance. 



WiCi is rate oxygen enters spavming bed through interchange. 

 WaCa is rate oxygen enters spawning bed through intragravel flov 

 WgCg is rate oxygen enters spawning bed through ground water. 

 WfCf is rate oxygen leaves spawning bed through intragravel flow 



VB is rate oxygen leaves spawning bed through biochemical oxygen demand. 



