RANGELAND HYDROLOGY BASIC CONCEPTS

Lamar Smith

Cascabel Ranch and Consulting

Carta Valley, Texas

OBJECTIVES

Understand water balance Understand basic erosion processes on rangeland Understand how brush control affects water yield and

erosion

PrecipitationRunoffInfiltrationEvaporationTranspirationTransmission lossesGroundwater recharge

Summarizing Hydrologic Data

Water balance – an accounting method

Annual Water balance for the Upper San Pedro River

Annual Water Balance for the Walnut Gulch Experimental Watershed

Ephemeral tributary to San Pedro River

RAINFALL12 in.

( 305 mm )

SURFACE DETENTION& INFILTRATION

10 in.( 254 mm )

EVAPORATION& TRANSPIRATION

10 in.( 254 mm )

ONSITE RUNOFF2 in.

( 51 mm )

CHANNEL LOSSES1 3/4 in. ( 45 mm )

SURFACE RUNOFF1/4 in. ( 6 mm )

EVAPORATION &TRANSPIRATION

FROM CHANNEL ANDVEGETATION ALONG STREAM

GROUND WATERRECHARGE

FROM CHANNEL

WATERSHED

EROSION PROCESSESRHEM MODEL

Climatic data Soil texture Slope length Slope shape Slope % % bunchgrass, forb/annual, shrubs, sod grass canopy

cover % rock, basal plant, litter and cryptogam cover

Most of these factors are climatic and site related – only vegetation is manageable

STREAM FLOW (WATER YIELD)

Subsurface = Springs Runoff = Flooding – dirt tanks, etc.

FFOLLIOTT AND THORUD – 1975

Increase in Water YieldPrecipitation

Mixed conifer = 6 inches 24+ inches

Ponderosa Pine = 2 inches 20-24 inches

Chaparral = 4 inches 16-20 inches

Pinyon – Juniper = 0 inches 16-20 inches

Grassland = 0 inches 12-16 inches

Desert Shrub = 0 inches 8-12 inches

MAIN POINTS

Infiltration – greater on sandy soils Depth of penetration – greater on sandy soils - gravel

increases Evaporation – less on sandy soils Deep percolation – greater on coarse soils – winter

precip Season of precipitation vs plant growth

DOES BRUSH CONTROL REDUCE SEDIMENT/EROSION?

MOST STUDIES SHOW THAT MESQUITE CONTROL REDUCES RUNOFF AND SOIL EROSION.

Mesquite reduces grass cover Increases patchiness of ground cover

STUDIES IN CREOSOTEBUSH ARE LESS DEFINITIVE

How treated? Roughness factor. How much grass response? Soil depth, texture? Storm intensity?

SO WHY DO BRUSH CONTROL?

Reduce erosion Reduce runoff intensity - flooding Increase species diversity Increase life form diversity Increase food for wildlife and livestock Improve biological production????