Specific Yield Calculator
Free Specific yield Calculator for soil & sediment mechanics. Enter variables to compute results with formulas and detailed steps.
Formula
Specific Yield (Sy) = Vdrained / Vtotal
Specific yield equals the volume of water that drains freely under gravity divided by the total volume of the saturated sample. Specific retention (Sr) equals porosity (n) minus specific yield: Sr = n - Sy. Together, Sy + Sr = n.
Worked Examples
Example 1: Sandy Aquifer Assessment
Problem: A 1,000 cm3 saturated sand sample drains 280 cm3 of water. The total porosity is 38%.
Solution: Specific Yield = (280 / 1000) x 100 = 28%\nSpecific Retention = 38% - 28% = 10%\nDrainable water = 1000 x 0.28 = 280 cm3\nRetained water = 1000 x 0.10 = 100 cm3
Result: Specific yield: 28% | Specific retention: 10% | Yield/Retention ratio: 2.80
Example 2: Clay-Silt Layer Analysis
Problem: A 500 cm3 clay-silt sample with 45% porosity only drains 25 cm3 under gravity.
Solution: Specific Yield = (25 / 500) x 100 = 5%\nSpecific Retention = 45% - 5% = 40%\nDrainable water = 500 x 0.05 = 25 cm3\nRetained water = 500 x 0.40 = 200 cm3
Result: Specific yield: 5% | Specific retention: 40% | Most water is retained
Frequently Asked Questions
What is specific yield in hydrogeology?
Specific yield is the ratio of the volume of water that drains freely from a saturated rock or soil under the influence of gravity to the total volume of the rock or soil. It represents the portion of pore water that is actually recoverable by pumping or drainage. Typical values range from 1-5% for clay, 10-20% for silt, and 20-35% for sand and gravel. It is a dimensionless quantity often expressed as a percentage.
How does specific yield differ from porosity?
Porosity measures the total void space in a material, including all pores regardless of size, while specific yield only measures the water that can drain freely under gravity. The difference between porosity and specific yield is called specific retention, which represents water held by molecular attraction and surface tension in small pores. Clay may have high porosity (40-60%) but very low specific yield (1-5%) because most water is retained in tiny pores.
Why is specific yield important for groundwater management?
Specific yield is critical for estimating the amount of groundwater available for extraction from an unconfined aquifer. It directly determines how much the water table will drop when water is pumped, and how much recharge is needed to restore levels. Water resource managers use specific yield to calculate sustainable pumping rates, estimate aquifer storage capacity, and plan well field designs. Without accurate specific yield data, groundwater reserves can be significantly over or underestimated.
What factors affect specific yield values?
The primary factors are grain size, grain shape, sorting, and compaction of the geological material. Coarse-grained, well-sorted sediments like clean gravel have the highest specific yields (25-35%) because large pores drain easily. Fine-grained materials like clay have low specific yields despite high porosity because capillary forces retain water. Depth of the water table, temperature (which affects water viscosity), and the duration of drainage also influence measured specific yield values in field tests.
What is APY vs APR in crypto yield?
APR is the simple annual rate without compounding. APY includes the effect of compounding. A 10% APR compounded daily equals roughly 10.52% APY. Always compare APY to APY for accurate yield comparisons.
How accurate are the results from Specific Yield Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.