ISO15709:2002(E) 2.2.2.8 hydraulic pressure Ph sum ofmatric, pneumatic and gravitational pressure NOTE 2.2.3 Head equivalent NOTE Head is expressed in metres. 2.2.3.1 head h head equivalent of soil waterpotential NOTE Subscripts as for potentials. 2.2.3.2 total head ht amount of work that must be done in order to transport, reversibly and isothermally, an infinitesimal quantity of underconsideration,dividedbytheweightofwatertransported 2.2.3.3 pneumatic head ha amount of work that must be done in order to transport, reversibly and isothermally, an infinitesimal quantity of wateridentical incompositiontothesoil waterfromapool atatmosphericpressure andatthe elevationofthepoint weight of water transported 2.2.3.4 gravitational head hg water identical in composition to the soil water from a pool at a specified elevation and at atmospheric pressure, to a similar pool at the elevation of the point under consideration, divided by the weight of water transported 2.2.3.5 matric head hm water identical in composition to the soil water from a pool at the elevation and the external gas pressure of the point under consideration, to the soil water at the point under consideration, divided by the weight of water transported 2.2.3.6 osmotic head ho water from a pool at the elevation and external gas pressure of the point under consideration, to a similar pool containingwater,identical incompositiontothe soil water,dividedbytheweightofwatertransported ISO 2002-All rights reserved ational Organization for Standardization license from IHS Not for Resale ISO15709:2002(E) 2.2.3.7 pressure head hp sum of matric and pneumatic heads NOTE In most cases ha is zero, in which case hp = hm 2.2.3.8 hydraulic head hh sum of matric, pneumatic and gravitational heads NOTE In most cases ha = h。= O, in which case hn = ht 3 Symbols and units acceleration due to gravity, in metres per second squared (m·s-2) h ha pneumatic head, in metres hg gravitational head, in metres hn hydraulic head = ha + hg + hm, in metres hm matric head, in metres ho osmotic head, in metres hp pressure head = tensiometer head = ha + hm, in metres ht total head = ha + hg + hm + ho + .., in metres m mass, in kilograms p pressure (pressure equivalent of the soil water potential), in newtons per square metre (N-m-2 = Pa) Pa pneumatic pressure, in pascals Pg gravitational pressure, in pascals Ph hydraulic pressure = Pa + Pg + Pm, in pascals Pm matric pressure, in pascals Po osmotic pressure, in pascals Pp pore water pressure = tensiometer pressure =Pa +Pm, in pascals Pt t time, in seconds 5 fcense from IHS Not for Resale ISO 15709:2002(E) velocity, in metres per second (m-s-1) v soil water flux density, in metres per second (m·s-1) ww water content mass fraction N vertical coordinate (positive upwards), in metres D water diffusivity, in metres squared per second (m2.s-1) K hydraulic conductivity, in metres per second (m·s-1) NOTE K(hm) is the hydraulic conductivity as a function of hm: K(g) is the hydraulic conductivity as a function of p. s degree of saturation, (dimensionless) V volume, in cubic metres water content volume fraction 元 volumetric extraction speed, per second (s-1) Pα density of the material α, in kilograms per cubic metre (kg-m-3) Pa density of the soil air, in kilograms per cubic metre (kg-m-3) Pb bulk density, the density of the three-phase mixture, in kilograms per cubic metre (kg-m-3) Pd dry density, the density of the dried solid, in kilograms per cubic metre (kg-m-3) Ps density of the solid matter (including the biological components), in kilograms per cubic metre (kg-m-3) Pw density of the water (soil solution), in kilograms per cubic metre (kg-m-3) Pa' partial bulk density of phase α, in kilograms per cubic metre (kg-m-3) Pa' partial bulk density of the soil air, in kilograms per cubic metre (kg-m-3) Ps partial bulk density of the solid particles and the dry bulk density (neglecting the bulk density of air), in kilograms per cubic metre (kg-m-3) Pw partial bulk densit