Desa Lapri terletak di Kabupaten Nunukan Sebatik Utara, dimana ketika musim hujan, sering terjadinya banjir/peluapan air yang di akibatkan sungai di Desa Lapri sudah tidak dapat menampung besarnya debit air sehingga terjadinya banjir. Penyebab terjadinya banjir di derah Aliran Sungai Lapri diakibatkan beberapa titik aliran Sungai Lapri terjadinya sedimentasi, longsor, dan penyumbatan aliran drainase. Pada penelitian ini bertujuan untuk mengetahui debit banjir eksisting Sungai Lapri dan dimensi saluran eksisting Sungai Lapri yang dapat mengalirkan debit banjir. Dari hasil analisis perhitungan diperoleh debit banjir rencana metode Nakayasu, dengan periode ulang 100 tahun (Q100) sebesar 86.947 m3/detik. Berdasarkan hasil analisis perhitungan, maka diperoleh debit banjir exsisting Sungai Lapri, untuk masing-masing STA sebagai berikut, STA 10 = 87.742 m3/detik, STA 9 = 87.953 m3/detik, STA 8 = 88.192 m3/detik, STA 7 = 88.481 m3/detik, STA 6 = 87.912 m3/detik, STA 5 = 88.028 m3/detik, STA 4 = 87.532 m3/detik, STA 3 = 87.730 m3/detik, STA 2 = 88.233 m3/detik, STA 1 = 87.874 m3/detik dan STA 0 = 88.624 m3/detik. Dari hasil debit tersebut, diperoleh dimensi penampang saluran Sungai Lapri yang mampu mengalirkan debit banjir rencana, dengan tinggi bagunan (h) = 5.37 m, dengan tinggi jagaan (W) = 1.64 m, dan lebar bawah saluran (b) = 6.20 m.

Lapri Village was located in North Sebatik Nunukan district. The flood often occurred there because Lapri river Village was unable to accommodate the amount of water discharge during the rainy season. The flood in the Lapri River Basin area was caused by sedimentation, landslides, and drainager blockage along Lapri River flow. This study aimed to determine the existing flood discharge and dimensions of existing Lapri River channel capable of draining the flood discharger. The result of analysis showed that planned flood discharger using the Nakayasu method with a return period of 100 years (Q100) was 86,947 m3/second. Thus, the existing flood discharger of Lapri River for each STA were found as follows : STA 10 was 87,742 m3/second, STA 9 was 87,953 m3/second, STA 8 was 88,192 m3/second, STA 7 was 88,481 m3/second, STA 6 was 87,912 m3/second, STA 5 was 88,028 m3/second, STA 4 was 87,532 m3/second, STA 3 was 87,730 m3/second, STA 2 was 88,233 m3/second, STA 1 was 87,874 m3/second and STA 0 was 88,624 m3/second. Based on the discharger results, Lapri River channel’s cross-sectional dimensions were capabe of draining flood discharger with 5,37 m building height, 1,64 m guard height, and 6,20 m channel of bottom width.