Analisis aliran permukaan, sedimen dan hara nitrogen, fosfor dan kebutuhan oksigen kimiawi dengan menggunakan Model AGNPS di Sub das dumpul

Abstract

Perencanaan pengelolaan DAS di Indonesia sampai saati ini masih belum dapat dilakukan dengan baik dan optimal sehingga seringkali menimbulkan fenomena-fenomena hidrologi yang merugikan lingkungan, seperti banjir, kekeringan, erosi, sedimentasi, penurunan kualitas air dan sebagainya. Salah satu bentuk alat bantu yang dapat digunakan dalam menentukan perencanaan pengelolaan DAS adalah model hidrologi yang mampu mngevaluasi dengan cepat serta mampu menduga dampak hidrologi dari perubahan – perubahan yang mungkin terjadi, baik secara alami maupun buatan manusia pada penggunaan lahan didalam DAS. Model hidrologi demikian dasar bagi pengembangan teknologi pengelolaan DAS yang rasional, efektif dan efisien.

Increasing population pressure on land has led to a reduction in prime agricultural land, particularly irrigated rice fields, as they are converted into industrial and residential areas. Currently, it is estimated that around 50,000 hectares of technical agricultural land are converted annually into non-agricultural uses. Such high-quality agricultural land is difficult to replace elsewhere because the remaining available land for agricultural expansion mostly consists of marginal, less fertile soils. To compensate for the annual loss of 50,000 hectares of fertile land, at least 250,000 hectares of marginal land are required to maintain rice production levels (Tejoyuwono et al., 1999).

In an effort to increase rice production, farming systems have been intensified and agricultural areas expanded even into steep, less productive, and erosion-prone lands. As a result, surface runoff and soil erosion have increased, leading to a decline in productivity due to nutrient loss from fertile topsoil layers. These conditions have contributed to environmental degradation in watersheds, increasing the extent of critical land. In 1984, there were 22 critical watersheds covering 9,699,000 hectares; by 1994, this had risen to 39 watersheds with 12,517,632 hectares of critical land, and by 2000, the number of critical watersheds reached 42, with a total critical land area continuing to expand.