Scientific Investigations Report 2006–5318
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5318
soilms_dpm.f
Distribute surplus moisture among soil layers (Bauer and Vaccaro, 1987; Bauer and Mastin, 1996).
This module executed only if there is surplus moisture after abstraction for plant interception. Surplus moisture is derived from precipitation as rainfall and or snowmelt or from irrigation. There are two soils moisture stores, 1) the saturated store that contains water above field capacity, and 2) the unsaturated store or field-capacity store that contains the water between wilting point and field capacity. Total water in each store (as fraction in a 6 inch layer) is the specific yield (spcyld) and total available water capacity (avlcap), respectively.
Surplus moisture is used to first fill each 6-inch layer in the field-capacity store from the top down. If there is remaining water, each 6-inch layer in the saturated store is filled from the bottom up. Any water in excess of filling both stores is saved as excess water (excess—quantity of water in excess of saturation). The excess water is first allowed to evaporate in soilevap_dpm.f, and any remaining excess is considered surface runoff in the module runoff_dpm.f. The soil is allowed to saturate with no percolation to subsoil (recharge) occurring. Recharge is controlled by user-specified infiltration rate, and it occurs after soils saturate. It is subsequently computed in module runoff_dpm.f or runtru_dpm.f.
July, 2004
unsatmax (calculated)
Maximum available water capacity for a soil for a HRU, in inches.
stormax (calculated)
Maximum saturated water capacity for a soil for a HRU, in inches.
avlcap
Total available water capacity (field capacity) for a soil association, no units-as decimal fraction.
spcyld
Specific yield for a soil association, no units-as decimal fraction.
solprm
Lateral permeability/conductivity for a soil association, in feet/day.
soil_type
Soil texture for a soil association, no units.
nlayer
Number of 6" layers for a soil association, no units.
strtsms
Initial soil moisture for all HRUs as fraction of field capacity-avlcap, no units.
strtpor
Initial soil saturation for all HRUs, as fraction of total effective porosity-spcyld, no units.
hru_soil
HRU soil type, no units. [basin]
cov_type
HRU cover type: land use/cover type, from 1-31, no units. [basin]
hru_appld
Application rate of irrigation water for HRU, in inches. [basin]
hru_irr_methd
Irrigation method for HRU: 0=above canopy, 1=all other. [basin]
smscapavg
Area-average of soil-moisture capacity for all HRUs, in inches.
smscapmin
Minimum of soil-moisture capacity for all HRUs, in inches.
smscapmax
Maximum of soil-moisture capacity for all HRUs, in inches.
satcapavg
Area-average of soil-saturation capacity for all HRUs, in inches.
satcapmin
Minimum of soil-saturation capacity for all HRUs, in inches.
satcapmax
Maximum of soil-saturation capacity for all HRUs, in inches.
sms
Soil moisture in unsaturated soil-moisture store, by layer, in inches.
sms_init
Initial soil moisture in unsaturated soil-moisture store, in inches.
storpor
Soil moisture in saturated soil-moisture store, by layer, in inches.
storpor_init
Initial soil moisture in saturated soil-moisture store, in inches.
excess
Quantity of water in excess of saturation, in inches.
hru_chngsm
Total change in soil moisture (saturated/unsaturated) for a day, in inches.
unsatcur
Current available water capacity for a HRU, in inches.
storcur
Current saturated water content for a HRU, in inches.
wght
HRU area as fraction of total area, as a fraction. [basin]
hru_rain
Quantity of rain for a HRU for a day, in inches. [snowpck]
hru_snomelt
Quantity of snowmelt for a HRU, in inches. [snowpck]
hru_irrigation
Amount of irrigation water applied to a HRU, in inches. [intrcp]
coefs
Daily values of 6 parameters for each of the crop-types, units vary. [cropcof]
The initialization part of the module first determines the total (maximum) quantity of water that can be stored in the unsaturated store and the saturated store for each HRU; these calculations are for all land uses/covers except water bodies and impervious surfaces. The minimum, maximum, and average values for the field capacity and saturated stores for the HRUs are then determined. Last, the initial water stored in each of the stores used for model starting conditions is calculated based on the input decimal percents for the field capacity store (strtsms) and the saturated store (strtpor). These calculations are not completed for surface water and impervious HRUs. The user sets strtpor greater than zero only when strtsms is equal to 1.0. That is, there can be no saturated water unless the field capacity (unsaturated) store is full.
The run part of the module first determines the current quantity of water in the unsaturated and saturated stores for all HRUs except those identified as water bodies or impervious (cov_type=10=16). The unsaturated quantity is stored in unsatcur and for each layer in sms_init for later calculating the daily change in the unsaturated store . The saturated quantity is stored in storcur and for each layer in storpor_init for later calculating the daily change in the saturated store.
The soil moisture addition calculations are then completed for each HRU based on the quantity of surplus water (sur) that is derived from snowmelt (hru_snomelt) and rainfall (hru_rain), and irrigation if it is applied below the canopy. If irrigation was applied above the canopy, the non-intercepted part was added to throughfall in the module intercept_dpm.f. If there is no surplus, the calculations are skipped for the HRU. In addition, all calculations are skipped for a HRU if it is a surface-water covered, and for the case of impervious HRUs, the calculations are skipped after setting the variable excess equal to the surplus water (sur).
For all other HRUs with surplus water, the unsaturated store is first filled from the top downward based on the quantity that can be stored to reach field capacity: unsatmax minus unsatcur. These calculations proceed layer by layer based on the quantity needed to fill a layer as
dry = wc – sms(i,n)
sur = sur – dry
sms(i,n) = wc
unsatcur (i) = unsatcur (i) + dry
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
nlayer is the number of layers for the association for this HRU,
n is the index of layers, from 1 to nlayer,
wc is the maximum unsaturated quantity of water that can be stored in a layer, in inches,
dry is the quantity that can be stored in the unsaturated stored for a layer, in inches , and
other variables as defined above.
If there is remaining surplus water (sur) after filling the unsaturated store, the saturated store is then filled layer by layer from the bottom upward. These calculations proceed layer by layer based on the quantity needed to fill a layer as
dry = sc – storpor(i,n)
sur = sur – dry
storpor(i,n)= sc
storcur(i) = storcur(i) + dry
where
nhru is the number of HRUs,
i is the index for the HRU, from 1 to nhru,
nlayer is the number of layers for the association for this HRU,
n is the index of layers, from 1 to nlayer,
sc is the maximum saturated quantity of water that can be stored in a layer in the saturated store, in inches,
dry is the quantity that can be stored in the saturated stored for a layer, in inches, and
other variables as defined above.
For the the above calculations, if sur becomes negative (all the surplus water was used filling a layer) then the total stored in the unsaturated/saturated store and the quantity stored in the last layer filled are readjusted based on adding the negative value of sur. However, if there is remaining surplus water (sur is positive), the amount remaining is put into the variable excess, which represents the amount of surplus water in excess of complete saturation of the soils for the HRU.
Bauer, H.H., and Mastin, M.C., 1997, Recharge from precipitation in three small glacial-till mantled catchments in the Puget Sound Lowlands: U. S. Geological Survey Water-Resources Investigations Report 96-4219, 119 p.
Bauer, H.H., and Vaccaro, J.J., 1987, Documentation of a deep percolation model for estimating ground-water recharge: U. S. Geological Survey Open-File Report 86-536, 180 p.
Henry H. Bauer and John J. Vaccaro
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Modified by:
John J. Vaccaro
U.S. Geological Survey
Washington Water Science Center
934 Broadway, Suite 300
Tacoma, WA 98402
Telephone: 253-552-1620
Fax: 253-552-1581
Email: jvaccaro@usgs.gov
U.S.
Department of the Interior | U.S. Geological
Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065318
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