2001-12-11_PERMIT FILE - C1981019 (4)

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Io and cla conte ts th th t il f th il h y n an e opso o e ot er two spo s treatments, and second, there was a greater degree of soil crusting on the nontop- soiled treatment as indicated by a higher modulus of rupture. Farmer and Richardson (1976) discussed the concept of macro-pores and micro-pores and the relationship of the pores to various hydrologic responses. Working with surface material from regraded surface coal mines in southeastern Montana, they determined macro-pore and micro- pore volume by saturating core samples with water and then draining them under 20 cm (0.02 bar) of water tension. The empty pore volume at 20 cm of water tension was considered macro-pore volume and the remaining pore volume was considered micro-pore. Their data tends to support the conclusion that a large volume of macro-pores promotes high infiltration • rates. Soil crusts formed on the soil surfaces during repeated cycles of applying simulated rainfall and drying, particularly on the more sodic surfaces. When the modulus of rupture was highest, indicating the strongest development of soil crust, the infiltration rate was lowest. Given the relationship between a large volume of macro-pores and high infiltration, and the relationship between the high modulus of rupture and law infiltration, perhaps the presence of macro-pores inhibits or delays the formation of soil crusts. In an effort to assess the effectiveness of reclamation efforts on surface coal mines in the Powder River Basin of Wyoming measured against conditions as they existed prior to mining, Lusby and Toy (1976) con- ducted an infiltration-erosion study using rainfall simulation at S.OB cm/hr (2 in/hr). The sediment yield was more than twice as much • on the regraded land as on the native range areas. Lusby and Toy cite