Assessing distributed mountain-block recharge in semiarid environments Huade Guan and John L. Wilson GSA Annual Meeting Nov. 10, 2004

What is distributed MBR? Recharge that occurs on hill slopes in the mountain block Precipitation Bedrock Soil Soil water Distributed MBR depends on across the soil- bedrock interface percolation Total MBR = distributed MBR + focused MBR Focused MBR occurs near and in stream channels and rivulets

What controls percolation to the bedrock? Our first generic simulation study looks at –Net infiltration = Infiltration – Evapotranspiration (ET) –Bedrock permeability –Soil type and thickness –Slope steepness –Bedrock topography (HYDRUS steady-state simulations, ET was not modeled)

The results have shown that major controls are net infiltration & bedrock permeability slope, soil and bedrock topography are not important. Granite FracturedGranite Slope = 0.3 Depression index = 0.1 Soil = sandy loam Two primary controls for percolation

Our first generic simulation study, using model of the soil and bedrock (HYDRUS) suggested major controls by –Net infiltration (infiltration – ET) –Bedrock permeability But what is “net infiltration”? We then added ET modeling in the simulations coupled with a surface energy partitioning model (SEP4HillET) –Considering effects of vegetation, slope steepness and aspect on potential E and Potential T What controls percolation to the bedrock?

Granite Tuff Granite Tuff Soil Vegetation control SN Annual P=565mm Vegetation cover=5% 4% 31% 17% Aspect effect 6% 7% 43% 22% Annual P=565mm Vegetation cover=50% SN Percolation: in % of Precip Aspect effect Soil and bedrock effects 3% 1% 23% 6% 2% 0.3% 16% 1.8% Slope aspects, vegetation cover, soil thickness for given bedrocks (transient, HYDRUS) More controls for percolation

Our first generic simulation study suggested major controls by –Net infiltration (infiltration – ET) –Bedrock permeability Our second generic simulation study suggested: –Bedrock properties (not only saturated K) –Vegetation coverage –Slope aspect (steepness as well) –Soil thickness (types as well) Now lets look at two sites in northern New Mexico What controls percolation to the bedrock?

Study areas 1.Jemez Mountains 2.Southern part of Sangre de Cristo Mountains 1 2

Why study these two sites ？ Basin oriented water balances suggest: Huntley (1979): total MBR ~200mm/yr =38% P in San Juan Mtns (volcanic rocks), and total MBR ~ 70mm/yr =14% P in Sangre de Cristo (granite and well-cemented sedimentary rock) McAda and Masiolek (1988): total MBR 50~100 mm/yr in Sangre de Cristo That is a lot recharge! But it is uncertain. Are these total MBR estimates reasonable? We'll test them by calculating the amount of distributed MBR. It should be less than the total.

Find percolation as a function of PET/P Where PET is annul potential ET P is annual precipitation Then, estimate PET and P maps for the study area From these maps and Percolation-- PET/P functions estimate distributed MBR Approaches for distributed MBR

LANL 1994 water-year time series data set, ponderosa site Macropore soil of uniform thickness (30 cm) Uniform vegetation coverage Uniform bedrock permeability for tuff ( m 2 ), and for fractured granite ( m 2 ) Only infiltration-excess runoff Some approximations for a hillslope in the mountains:

Percolation=f(PET/P) HYDRUS sim. Bedrock=tuff Slope =0.1 (not to scale) Slope =0.2 Top-slope Mid-slope

Percolation=f(PET/P) HYDRUS sim. Bedrock=tuff Bedrock=granite 0.1 slope

Percolation=f(PET/P) HYDRUS sim. Bedrock=tuff Bedrock=granite Percolation = f1(PET/P) Percolation = f2(PET/P)

How is PET/P obtained ? Next, we need spatial distributed annual precipitation (P) –Estimated by a geostatistic model ASOADeK And spatial distributed annual PET –Estimated by Hargreaves 1985 and SEP4HillET

Precipitation mapping: ASOADeK and de-trended kriging Spatial trendElevationSlope aspect and prevailing wind Sum of 12 monthly precipitation

PET mapping: Hargreaves SEP4HillET R a : daily extraterrestrial solar radiation in equivalent depth of water R a is dependent of the slope steepness and aspect, solved using SEP4HillET model Slope aspect & steepness Seasonal & altitudinal effects

M1 M4 M2 M3 M5 M6 M12 M9 M11 M10 M8 M7 Ratio of R a on sloped surface to that on flat surface (from SEP4HillET) N S N Winter Summer

Temperature mapping Topographic corrected geostatistical interpolations of temperature Daily maximum temperatureDaily minimum temperature Regression (Tmax~Z) Regression (Tmin~Z): M4, 5, 6, 7, 8, 9 Kriging Tmin: M1, 2, 3, 10, 11, 12

Maps of PET Jemez Mountains Sangre de Cristo Mountains

Maps of potential distributed MBR at hypothetical northern NM mountains Jemez MountainsSangre de Cristo Mountains Min: 0 Max: 193 Mean: 47Median: 42 Min: 0 Max: 113 Mean: 16Median: 0.44 Unit: mm/yr

Conclusion Mtns.Previous studies This study (Total MBR) (Max. rate of distributed MBR) Sangre’s mm/yr16 mm/yr Jemez/47 mm/yr San Juan200 mm/yr Distributed MBR << Total MBR Focused MBR, in stream channels and rivulets appears to be the most important component of MBR for these two mountain regions and both rock types. This is still a work in progress, and didn't use all spatial information on soil and vegetative cover, etc.

ain Thank you ！