SOIL-WATER PROPERTIES COMPUTED FROM TRANSIENT FLOW DATA

A METHOD IS GIVEN FOR CALCULATING WATER CONDUCTIVITY (K) OF UNSATURATED SOIL BY THE USE OF DATA OBTAINED DURING TRANSIENT CHANGES OF MOISTURE CONTENT (BETA) AND SUCTION HEAD (H) ALONG A HORIZONTAL SOIL COLUMN. A SOIL MOISTURE CHARACTERISTIC CURVE WAS OBTAINED FROM THE DATA. ABSOLUTE VALUES OF THE SLOPES OF THE LATTER CURVE, THE DIFFERENTIAL WATER CAPACITY (C), PERTAINING TO THE EXPERIMENTAL VALUES OF H WERE THEN USED TO CALCULATE SOIL-WATER DIFFUSIVITY (D) FROM THE EQUATION, D-K/C. THE EXPERIMENTAL PROCEDURE DOES NOT INVOLVE BOUNDARY CONDITIONS THAT, IN SOME PROCEDURES, ARE DIFFICULT TO EVALUATE, NOR ARE STEADY-STATE AND EQUILIBRIUM-FLOW CONDITIONS REQUIRED. DATA FOR MOST SOILS WAS OBTAINED IN FROM 8 TO 12 DAYS. A PROGRAM WAS WRITTEN IN FORTRAN IV LANGUAGE FOR USE WITH THE IBM 7040 DATA PROCESSING SYSTEM. THE SOLUTION OF THE PROBLEM WAS REDUCED TO A ROUTINE THAT SAVES SEVERAL HOURS OF HAND CALCULATIONS. VALUES OF K, C, AND D FOR FIELD CORES AND LABORATORY COMPACTED SOIL COLUMNS WERE MEASURED OVER THE RANGE OF 50 EQUAL TO H EQUAL TO 750 CM OF WATER. RELATIVE ERROR VALUES BETWEEN MEASURED VALUES OF K AND THOSE CALCULATED FROM THE EQUATION K EQUALS CH WERE LESS THAN 50% IN 83% OF 288 MEASUREMENTS. RELATIVE ERROR VALUES BETWEEN MEASURED VALUES OF D AND THOSE CALCULATED FROM THE EQUATION D EQUALS ALPHA EXP BETA WERE LESS THAN 50% IN 74% OF THE 288 MEASUREMENTS. THE CONSTANTS, C, D, ALPHA, AND BETA ARE EMPIRICAL FOR A GIVEN SOIL. WATER CONDUCTIVITY VALUES WERE SHOWN TO BE INDEPENDENT OF HYDRAULIC GRADIENTS OVER A WIDE RANGE OF GRADIENT VALUES. /A/RRL/

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Filing Info

  • Accession Number: 00237253
  • Record Type: Publication
  • Source Agency: Road Research Laboratory /UK
  • Files: TRIS
  • Created Date: Jun 26 1970 12:00AM