加壓式地下滴灌模擬之初步探討

A Preliminary Study of Pressurized Subsurface Drip Irrigation Modeling

蔡存孝(Tswn-Syau Tsay) ； 朱聖浩(Shen-Haw Ju) ； 黃振昌(Cheng-Chang Huang)

《農業工程學報》 53卷1期 (2007/03) Pp. 22-31

https://doi.org/10.29974/JTAE.200703.0003

摘要

由於人類文明的發展迅速，對於水資源的需求日益增加，因此，全球的缺水問題已經從乾旱地區及半乾旱地區衍生到水量供應充分的地區，所幸的是，在水量供應不足的狀況下，缺水灌溉已由現場實驗的觀察資料中，証實為可以在有限條件下供應作物的需水，且對於作物生產量不會產生太大的影響。在缺水灌溉的過程中，土壤水份含量必須介於田間容水量及田間容水量與永久凋萎點的平均值之間。由於地下滴灌(SDI)的優點，可以滿足缺水灌溉的需求，但使用SDI容易產生兩個問題，(1)因為SDI灌溉水量較小，使用低壓力灌溉，容易造成滴灌頭(emitter)阻塞問題；(2)當土壤水份含量低於土壤飽和含水量時，土壤的水力傳導係數(hydraulic conductivity)遠較飽和土壤水力傳導係數低，使土壤水份的流動速率降低，增加了滿足植物的水量需求的灌溉時間。為加速土壤水份的擴散速率以減少灌溉時問，並降低SDI的低壓力灌溉阻塞問題，本研究採用加壓方式增加SDI灌溉水量。本文藉由Richards公式及van Genuchten方程式以數值模擬的方法，增加灌溉壓力，藉以了解加壓式SDI在灌溉的過程土壤濕峰的發展情形。以本文中所舉的模擬範例而言，對於同一種土壤，同一施灌條件下，「可能最大土壤水份含量」隨著灌溉觀測位置及灌溉水量的而異，不同的起始土壤水份含量（或起始土壤張力）則不會影響「可能最大土壤水份含量」，且「可能最大土壤水份含量」與灌溉水量呈正相關的關係。

關鍵字

地下滴灌 ； 非飽和地下水流 ； 模擬

並列摘要

As the fast development of human culture and increasing demanding of water resources, global water scarcity extends from arid and semi-arid areas to water resources abundant areas. Fortunately, recent field research indicated that deficit irrigation is appropriate for supplying crops water for obtaining reasonable yield under some conditions. According to the characteristics of deficit irrigation, moisture content should be maintained between at field capacity (FC) and the average of FC and the permanent wilting point (PWP). The advantages of SDI are sufficient deficit irrigation. However, the low flow rate and low pressure characteristics of SDI usually cause emitter clogging. Besides, the unsaturated hydraulic conductivity is much less than the saturated one, which takes much more irrigation time to satisfy crops water requirement. A pressurized SDI was proposed in this paper to overcome problems of emitter clogging and long irrigation time requirement. A numerical model was developed applying Richards equation and van Genuchten's function to explore the wetting front development of SDI. The ”Probably Maximum Soil Moisture Content” depends upon observation locations and irrigation rate for the cases presented in this paper. ”Probably Maximum Soil Moisture Content” is independent of the initial soil moisture content and is proportional to the irrigation rate.

並列關鍵字

Subsurface drip irrigation ； Unsaturated flow ； Modeling